1.
Tempel 1
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Tempel 1 is a periodic Jupiter-family comet discovered by Wilhelm Tempel in 1867. It completes an orbit of the Sun every 5.5 years, Tempel 1 was the target of the Deep Impact space mission, which photographed a deliberate high-speed impact upon the comet in 2005. It was re-visited by the Stardust spacecraft on February 14,2011, Tempel 1 was discovered on April 3,1867, by Wilhelm Tempel, an astronomer working in Marseille. At the time of discovery, it approached perihelion once every 5.68 years and it was subsequently observed in 1873 and in 1879. Photographic attempts during 1898 and 1905 failed to recover the comet, in fact, its orbit had changed. Tempel 1s orbit occasionally brings it close to Jupiter to be altered. This occurred in 1881, lengthening the period to 6.5 years. Perihelion also changed, increasing by 50 million kilometres, rendering the far less visible from Earth. Tempel 1 was rediscovered 13 orbits later in 1967, after British astronomer Brian G. Marsden performed precise calculations of the orbit that took into account Jupiters perturbations. These approaches moved Tempel 1 into its present libration around the 1,2 resonance with Jupiter, despite an unfavorable 1967 return, Elizabeth Roemer of the Catalina Observatory took several photographs. A single image does not allow a computation, so the next return had to be awaited. Roemer and L. M. Vaughn recovered the comet on January 11,1972, the comet became widely observed, reached a maximum brightness of magnitude 11 during May, and was last seen on July 10. Since that time the comet has been seen at every apparition and its orbital period is 5.515 years. Tempel 1 is not a comet, its brightest apparent magnitude since discovery has been 11. Its nucleus measures 7.6 km ×4.9 km, measurements taken by the Hubble Space Telescope in visible light and the Spitzer Space Telescope in infrared light suggest a low albedo of only 4%. A two-day rotation rate was also determined, on 4 July 2005 at 05,52 UTC, Tempel 1 was deliberately struck by one component of the NASA Deep Impact probe, one day before perihelion. The impact was photographed by the component of the probe. The impact was observed by earthbound and space telescopes, which recorded a brightening of several magnitudes
2.
Comet
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A comet is an icy small Solar System body that, when passing close to the Sun, warms and begins to evolve gasses, a process called outgassing. This produces an atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of radiation and the solar wind acting upon the nucleus of the comet. Comet nuclei range from a few hundred metres to tens of kilometres across and are composed of collections of ice, dust. The coma may be up to 15 times the Earths diameter, if sufficiently bright, a comet may be seen from the Earth without the aid of a telescope and may subtend an arc of 30° across the sky. Comets have been observed and recorded since ancient times by many cultures, Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years. Short-period comets originate in the Kuiper belt or its associated scattered disc, long-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star. Long-period comets are set in motion towards the Sun from the Oort cloud by gravitational perturbations caused by passing stars, hyperbolic comets may pass once through the inner Solar System before being flung to interstellar space. The appearance of a comet is called an apparition, Comets are distinguished from asteroids by the presence of an extended, gravitationally unbound atmosphere surrounding their central nucleus. This atmosphere has parts termed the coma and the tail, however, extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble small asteroids. Asteroids are thought to have a different origin from comets, having formed inside the orbit of Jupiter rather than in the outer Solar System, the discovery of main-belt comets and active centaur minor planets has blurred the distinction between asteroids and comets. As of November 2014 there are 5,253 known comets, however, this represents only a tiny fraction of the total potential comet population, as the reservoir of comet-like bodies in the outer Solar System is estimated to be one trillion. Roughly one comet per year is visible to the eye, though many of those are faint. Particularly bright examples are called Great Comets, the word comet derives from the Old English cometa from the Latin comēta or comētēs. That, in turn, is a latinisation of the Greek κομήτης, Κομήτης was derived from κομᾶν, which was itself derived from κόμη and was used to mean the tail of a comet. The astronomical symbol for comets is ☄, consisting of a disc with three hairlike extensions. The solid, core structure of a comet is known as the nucleus, cometary nuclei are composed of an amalgamation of rock, dust, water ice, and frozen gases such as carbon dioxide, carbon monoxide, methane, and ammonia. As such, they are described as dirty snowballs after Fred Whipples model
3.
Rock (geology)
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Rock or stone is a natural substance, a solid aggregate of one or more minerals or mineraloids. For example, granite, a rock, is a combination of the minerals quartz, feldspar. The Earths outer solid layer, the lithosphere, is made of rock, rock has been used by mankind throughout history. The minerals and metals found in rocks have been essential to human civilization, three major groups of rocks are defined, igneous, sedimentary, and metamorphic. The scientific study of rocks is called petrology, which is a component of geology. At a granular level, rocks are composed of grains of minerals, the aggregate minerals forming the rock are held together by chemical bonds. The types and abundance of minerals in a rock are determined by the manner in which the rock was formed, many rocks contain silica, a compound of silicon and oxygen that forms 74. 3% of the Earths crust. This material forms crystals with other compounds in the rock, the proportion of silica in rocks and minerals is a major factor in determining their name and properties. Rocks are geologically classified according to such as mineral and chemical composition, permeability, the texture of the constituent particles. These physical properties are the end result of the processes that formed the rocks, over the course of time, rocks can transform from one type into another, as described by the geological model called the rock cycle. These events produce three general classes of rock, igneous, sedimentary, and metamorphic, the three classes of rocks are subdivided into many groups. However, there are no hard and fast boundaries between allied rocks, hence the definitions adopted in establishing rock nomenclature merely correspond to more or less arbitrary selected points in a continuously graduated series. Igneous rock forms through the cooling and solidification of magma or lava and this magma can be derived from partial melts of pre-existing rocks in either a planets mantle or crust. Typically, the melting of rocks is caused by one or more of three processes, an increase in temperature, a decrease in pressure, or a change in composition, igneous rocks are divided into two main categories, plutonic rock and volcanic. Plutonic or intrusive rocks result when magma cools and crystallizes slowly within the Earths crust, a common example of this type is granite. Volcanic or extrusive rocks result from magma reaching the surface either as lava or fragmental ejecta, the chemical abundance and the rate of cooling of magma typically forms a sequence known as Bowens reaction series. Most major igneous rocks are found along this scale, about 64. 7% of the Earths crust by volume consists of igneous rocks, making it the most plentiful category. Of these, 66% are basalts and gabbros, 16% are granite, only 0. 6% are syenites and 0. 3% peridotites and dunites
4.
Dust
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Dust is fine particles of matter. It generally consists of particles in the atmosphere that come from sources such as soil, dust lifted by weather, volcanic eruptions. House dust mites are present indoors wherever humans live, positive tests for dust mite allergies are extremely common among people with asthma. Dust mites are microscopic arachnids whose primary food is dead skin cells. They and their feces and other allergens they produce are major constituents of house dust and they are generally found on the floor and other surfaces until disturbed. It could take somewhere between twenty minutes and two hours for dust mites to settle back down out of the air, Dust mites are a nesting species that prefers a dark, warm, and humid climate. They flourish in mattresses, bedding, upholstered furniture, and carpets and their feces include enzymes that are released upon contact with a moist surface, which can happen when a person inhales, and these enzymes can kill cells within the human body. House dust mites did not become a problem until humans began to use textiles, such as western style blankets and clothing. Atmospheric or wind-borne dust, also known as aeolian dust, comes from arid and dry regions where high velocity winds are able to remove mostly silt-sized material, Dust in the atmosphere is produced by saltation and sandblasting of sand-sized grains, and it is transported through the troposphere. This airborne dust is considered an aerosol and once in the atmosphere, saharan dust in particular can be transported and deposited as far as the Caribbean and the Amazon basin, and may affect air temperatures, cause ocean cooling, and alter rainfall amounts. Dust in the Middle East has been a historic phenomenon, recently, because of climate change and the escalating process of desertification, the problem has worsened dramatically. As a multi-factor phenomenon, there is not yet a consensus on the sources or potential solutions to the problem. In Iran, the dust is already affecting more than 5 million people directly, in the province of Khuzestan it has led to the severe reduction of air quality. The amount of pollutants in the air has surpassed more than 50 times the normal level several times in a year, recently, initiatives such as Project-Dust have been established to directly study the Middle Eastern dust. Dust kicked up by vehicles traveling on roads may make up 33% of air pollution, road dust consists of deposits of vehicle exhausts and industrial exhausts, particles from tire and brake wear, dust from paved roads or potholes, and dust from construction sites. Road dust is a significant source contributing to the generation and release of particulate matter into the atmosphere. Control of road dust is a significant challenge in urban areas, road dust may be suppressed by mechanical methods like street sweeper vehicles equipped with vacuum cleaners, vegetable oil sprays, or with water sprayers. Improvements in automotive engineering have reduced the amount of PM10s produced by road traffic, coal dust is responsible for the lung disease known as pneumoconiosis, including black lung disease that occurs among coal miners
5.
Gas
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Gas is one of the four fundamental states of matter. A pure gas may be made up of atoms, elemental molecules made from one type of atom. A gas mixture would contain a variety of pure gases much like the air, what distinguishes a gas from liquids and solids is the vast separation of the individual gas particles. This separation usually makes a colorless gas invisible to the human observer, the interaction of gas particles in the presence of electric and gravitational fields are considered negligible as indicated by the constant velocity vectors in the image. One type of commonly known gas is steam, the gaseous state of matter is found between the liquid and plasma states, the latter of which provides the upper temperature boundary for gases. Bounding the lower end of the temperature scale lie degenerative quantum gases which are gaining increasing attention, high-density atomic gases super cooled to incredibly low temperatures are classified by their statistical behavior as either a Bose gas or a Fermi gas. For a comprehensive listing of these states of matter see list of states of matter. The only chemical elements which are stable multi atom homonuclear molecules at temperature and pressure, are hydrogen, nitrogen and oxygen. These gases, when grouped together with the noble gases. Alternatively they are known as molecular gases to distinguish them from molecules that are also chemical compounds. The word gas is a neologism first used by the early 17th-century Flemish chemist J. B. van Helmont, according to Paracelsuss terminology, chaos meant something like ultra-rarefied water. An alternative story is that Van Helmonts word is corrupted from gahst and these four characteristics were repeatedly observed by scientists such as Robert Boyle, Jacques Charles, John Dalton, Joseph Gay-Lussac and Amedeo Avogadro for a variety of gases in various settings. Their detailed studies ultimately led to a relationship among these properties expressed by the ideal gas law. Gas particles are separated from one another, and consequently have weaker intermolecular bonds than liquids or solids. These intermolecular forces result from interactions between gas particles. Like-charged areas of different gas particles repel, while oppositely charged regions of different gas particles attract one another, transient, randomly induced charges exist across non-polar covalent bonds of molecules and electrostatic interactions caused by them are referred to as Van der Waals forces. The interaction of these forces varies within a substance which determines many of the physical properties unique to each gas. A comparison of boiling points for compounds formed by ionic and covalent bonds leads us to this conclusion, the drifting smoke particles in the image provides some insight into low pressure gas behavior
6.
Sun
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The Sun is the star at the center of the Solar System. It is a perfect sphere of hot plasma, with internal convective motion that generates a magnetic field via a dynamo process. It is by far the most important source of energy for life on Earth. Its diameter is about 109 times that of Earth, and its mass is about 330,000 times that of Earth, accounting for about 99. 86% of the total mass of the Solar System. About three quarters of the Suns mass consists of hydrogen, the rest is mostly helium, with smaller quantities of heavier elements, including oxygen, carbon, neon. The Sun is a G-type main-sequence star based on its spectral class and it formed approximately 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud. Most of this matter gathered in the center, whereas the rest flattened into a disk that became the Solar System. The central mass became so hot and dense that it eventually initiated nuclear fusion in its core and it is thought that almost all stars form by this process. The Sun is roughly middle-aged, it has not changed dramatically for more than four billion years and it is calculated that the Sun will become sufficiently large enough to engulf the current orbits of Mercury, Venus, and probably Earth. The enormous effect of the Sun on Earth has been recognized since prehistoric times, the synodic rotation of Earth and its orbit around the Sun are the basis of the solar calendar, which is the predominant calendar in use today. The English proper name Sun developed from Old English sunne and may be related to south, all Germanic terms for the Sun stem from Proto-Germanic *sunnōn. The English weekday name Sunday stems from Old English and is ultimately a result of a Germanic interpretation of Latin dies solis, the Latin name for the Sun, Sol, is not common in general English language use, the adjectival form is the related word solar. The term sol is used by planetary astronomers to refer to the duration of a solar day on another planet. A mean Earth solar day is approximately 24 hours, whereas a mean Martian sol is 24 hours,39 minutes, and 35.244 seconds. From at least the 4th Dynasty of Ancient Egypt, the Sun was worshipped as the god Ra, portrayed as a falcon-headed divinity surmounted by the solar disk, and surrounded by a serpent. In the New Empire period, the Sun became identified with the dung beetle, in the form of the Sun disc Aten, the Sun had a brief resurgence during the Amarna Period when it again became the preeminent, if not only, divinity for the Pharaoh Akhenaton. The Sun is viewed as a goddess in Germanic paganism, Sól/Sunna, in ancient Roman culture, Sunday was the day of the Sun god. It was adopted as the Sabbath day by Christians who did not have a Jewish background, the symbol of light was a pagan device adopted by Christians, and perhaps the most important one that did not come from Jewish traditions
7.
Sublimation (phase transition)
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Sublimation is the phase transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase. Sublimation is a process that occurs at temperatures and pressures below a substances triple point in its phase diagram. The reverse process of sublimation is deposition or desublimation, in which a substance directly from a gas to a solid phase. Sublimation has also used as a generic term to describe a solid-to-gas transition followed by a gas-to-solid transition. At normal pressures, most chemical compounds and elements possess three different states at different temperatures, in these cases, the transition from the solid to the gaseous state requires an intermediate liquid state. The pressure referred to is the pressure of the substance. So, all solids that possess an appreciable vapor pressure at a temperature usually can sublimate in air. The term sublimation refers to a change of state and is not used to describe transformation of a solid to a gas in a chemical reaction. For example, the dissociation on heating of ammonium chloride into hydrogen chloride and ammonia is not sublimation. Similarly the combustion of candles, containing paraffin wax, to carbon dioxide and water vapor is not sublimation, sublimation requires additional energy and is an endothermic change. The enthalpy of sublimation can be calculated by adding the enthalpy of fusion, solid carbon dioxide sublimes everywhere along the line below the triple point, whereas its melting into liquid CO2 can occur only along the line at pressures and temperatures above the triple point. Snow and ice sublime, although more slowly, at temperatures below the freezing/melting point temperature line at 0 °C for most pressures, in freeze-drying, the material to be dehydrated is frozen and its water is allowed to sublime under reduced pressure or vacuum. The loss of snow from a snowfield during a spell is often caused by sunshine acting directly on the upper layers of the snow. Ablation is a process that includes sublimation and erosive wear of glacier ice, naphthalene, an organic compound commonly found in pesticide such as mothball also sublimes. It sublimes easily because it is made of molecules and has van der Waals intermolecular forces. Naphthalene is a solid that sublimes at atmospheric temperature with the sublimation point at around 80˚C or 176˚F. At low temperature, its pressure is high enough,1 mmHg at 53˚C. On the cool surface, the sublimated vapour will be solidified to form a needle-like crystal, iodine produces fumes on gentle heating
8.
Atmosphere
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An atmosphere is a layer of gases surrounding a planet or other material body, that is held in place by the gravity of that body. An atmosphere is likely to be retained if the gravity it is subject to is high. The atmosphere of Earth is mostly composed of nitrogen, oxygen, argon with carbon dioxide, the atmosphere helps protect living organisms from genetic damage by solar ultraviolet radiation, solar wind and cosmic rays. Its current composition is the product of billions of years of modification of the paleoatmosphere by living organisms. The term stellar atmosphere describes the region of a star. Stars with sufficiently low temperatures may form compound molecules in their outer atmosphere, Atmospheric pressure is the force per unit area that is applied perpendicularly to a surface by the surrounding gas. It is determined by a gravitational force in combination with the total mass of a column of gas above a location. On Earth, units of air pressure are based on the recognized standard atmosphere. It is measured with a barometer, the pressure of an atmospheric gas decreases with altitude due to the diminishing mass of gas above. The height at which the pressure from an atmosphere declines by a factor of e is called the height and is denoted by H. For such an atmosphere, the pressure declines exponentially with increasing altitude. However, atmospheres are not uniform in temperature, so the determination of the atmospheric pressure at any particular altitude is more complex. Surface gravity, the force that holds down an atmosphere, differs significantly among the planets, for example, the large gravitational force of the giant planet Jupiter is able to retain light gases such as hydrogen and helium that escape from objects with lower gravity. Thus, the distant and cold Titan, Triton, and Pluto are able to retain their atmospheres despite their relatively low gravities, rogue planets, theoretically, may also retain thick atmospheres. Since a collection of gas molecules may be moving at a range of velocities. Lighter molecules move faster than ones with the same thermal kinetic energy. It is thought that Venus and Mars may have lost much of their water when, after being photo dissociated into hydrogen and oxygen by solar ultraviolet, Earths magnetic field helps to prevent this, as, normally, the solar wind would greatly enhance the escape of hydrogen. However, over the past 3 billion years Earth may have lost gases through the polar regions due to auroral activity
9.
Coma (cometary)
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The coma is the nebulous envelope around the nucleus of a comet, formed when the comet passes close to the Sun on its highly elliptical orbit, as the comet warms, parts of it sublimes. This gives a comet a fuzzy appearance when viewed in telescopes and distinguishes it from stars, the word coma comes from the Greek kome, which means hair and is the origin of the word comet itself. The coma is generally made of ice and comet dust, water dominates up to 90% of the volatiles that outflow from the nucleus when the comet is within 3-4 AU of the Sun. The parent molecule is destroyed primarily through photodissociation and to a smaller extent photoionization. The solar wind plays a role in the destruction of water compared to photochemistry. Larger dust particles are left along the orbital path while smaller particles are pushed away from the Sun into the comets tail by light pressure. Comas typically grow in size as comets approach the Sun, and they can be as large as the diameter of Jupiter, about a month after an outburst in October 2007, comet 17P/Holmes briefly had a tenuous dust atmosphere larger than the Sun. The Great Comet of 1811 also had a coma roughly the diameter of the Sun, even though the coma can become quite large, its size can actually decrease about the time it crosses the orbit of Mars around 1.5 AU from the Sun. At this distance the solar wind becomes strong enough to blow the gas and dust away from the coma, Comets were found to emit X-rays in late-March 1996. This surprised researchers, because X-ray emission is associated with very high-temperature bodies. This ripping off leads to the emission of X-rays and far ultraviolet photons, with basic Earth-surface based telescope and some technique, the size of the Coma can be calculated. Called the drift method, one locks the telescope in position and that time multiplied by the cosine of comets declination, times.25 should equal the comas diameter in arcminutes. If the distance to the comet is known, then the apparent size of the coma can be determined. In 2015, it was noted that the ALICE instrument on the ESA Rosetta spacecraft to comet 67/P, detected hydrogen, oxygen, carbon and nitrogen in the Coma, which they also called the Comets atmosphere. Alice is a spectrograph, and it found that electrons created by UV light were colliding and breaking up molecules of water. OAO-2 discovered large halos of hydrogen gas around comets, space probe Giotto detected hydrogen ions at distance of 7.8 million km away from Halley when it did close flyby of the comet in 1986. A hydrogen gas halo was detected to be 15 times the diameter of Sun and this triggered NASA to point the Pioneer Venus mission at the Comet, and it was determined that the Comet emitting 12 tons of water per second. The hydrogen gas emission has not been detected from Earths surface because those wavelengths are blocked by the atmosphere, the process by which water is broken down into hydrogen and oxygen was studied by the ALICE instrument aboard the Rosetta spacecraft
10.
Radiation pressure
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Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. Radiation pressure implies an interaction between radiation and bodies of various types, including clouds of particles or gases. The interactions can be absorption, reflection, or some of both, bodies also emit radiation and thereby experience a resulting pressure. For example, had the effects of the radiation pressure on the spacecraft of the Viking program been ignored. This article addresses the macroscopic aspects of radiation pressure, detailed quantum mechanical aspects of interactions are addressed in specialized articles on the subject. The details of how photons of various wavelengths interact with atoms can be explored through links in the See also section, johannes Kepler put forward the concept of radiation pressure back in 1619 to explain the observation that a tail of a comet always points away from the Sun. The pressure is very feeble, but can be detected by allowing the radiation to fall upon a delicately poised vane of reflective metal in a Nichols radiometer, radiation pressure can be analyzed as interactions by either electromagnetic waves or particles. The waves and photons both have the property of momentum, which allows their interchangeability under classical conditions, according to Maxwells theory of electromagnetism, an electromagnetic wave carries momentum, which can be transferred to a reflecting or absorbing surface hit by the wave. The component of the normal to the surface creates the pressure on the surface. The component tangent to the surface does not contribute to the pressure, electromagnetic radiation is quantized in particles called photons, the particle aspect of its wave–particle duality. Photons are best explained by quantum mechanics, although photons are zero-rest mass particles, they have the properties of energy and momentum, and thus exhibit the property of mass as they travel at light speed. The momentum of a photon is given by, p = h λ where p is momentum, h is Plancks constant, λ is wavelength and this expression shows the wave–particle duality. E = p c is the relationship where E is the energy. Then p = E c The generation of radiation pressure results from the property of photons, specifically. The surface exerts a force on the photons in changing their momentum by Newtons Second Law, a reactive force is applied to the body by Newtons Third Law. The orientation of a reflector determines the component of normal to its surface. Each factor contributes a cosine function, reducing the pressure on the surface, bodies radiate thermal energy according to their temperature. The emissions are electromagnetic radiation, and therefore have the properties of energy, the energy leaving a body tends to reduce its temperature
11.
Solar wind
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The solar wind is a stream of charged particles released from the upper atmosphere of the Sun. This plasma consists of electrons, protons and alpha particles with thermal energies between 1.5 and 10 keV. Embedded within the plasma is the interplanetary magnetic field. The solar wind varies in density, temperature and speed over time and its particles can escape the Suns gravity because of their high energy resulting from the high temperature of the corona, which in turn is a result of the coronal magnetic field. At a distance of more than a few radii from the sun. The flow of the wind is no longer supersonic at the termination shock. The Voyager 2 spacecraft crossed the shock more than five times between 30 August and 10 December 2007, Voyager 2 crossed the shock about a billion kilometers closer to the Sun than the 13.5 billion kilometer distance where Voyager 1 came upon the termination shock. The spacecraft moved outward through the shock into the heliosheath. Other related phenomena include the aurora, the tails of comets that always point away from the Sun. The existence of flowing outward from the Sun to the Earth was first suggested by British astronomer Richard C. In 1859, Carrington and Richard Hodgson independently made the first observation of what would later be called a solar flare, george FitzGerald later suggested that matter was being regularly accelerated away from the Sun and was reaching the Earth after several days. In 1910 British astrophysicist Arthur Eddington essentially suggested the existence of the wind, without naming it. The idea never caught on even though Eddington had also made a similar suggestion at a Royal Institution address the previous year. In the latter case, he postulated that the material consisted of electrons while in his study of Comet Morehouse he supposed them to be ions. The first person to suggest that the material consisted of both ions and electrons was Kristian Birkeland. His geomagnetic surveys showed that activity was nearly uninterrupted. In 1916, Birkeland proposed that, From a physical point of view it is most probable that solar rays are neither exclusively negative nor positive rays, in other words, the solar wind consists of both negative electrons and positive ions. Three years later in 1919, Frederick Lindemann also suggested that particles of both polarities, protons as well as electrons, come from the Sun
12.
Albedo
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Albedo is a measure for reflectance or optical brightness. It is dimensionless and measured on a scale from zero to one, surface albedo is defined as the ratio of radiation reflected to the radiation incident on a surface. The proportion reflected is not only determined by properties of the surface itself and these factors vary with atmospheric composition, geographic location and time. While bi-hemispherical reflectance is calculated for an angle of incidence. The temporal resolution may range from seconds to daily, seasonal or annual averages, unless given for a specific wavelength, albedo refers to the entire spectrum of solar radiation. Due to measurement constraints, it is given for the spectrum in which most solar energy reaches the surface. This spectrum includes visible light, which explains why surfaces with a low albedo appear dark, albedo is an important concept in climatology, astronomy, and environmental management. The term albedo was introduced into optics by Johann Heinrich Lambert in his 1760 work Photometria, any albedo in visible light falls within a range of about 0.9 for fresh snow to about 0.04 for charcoal, one of the darkest substances. Deeply shadowed cavities can achieve an effective albedo approaching the zero of a black body, when seen from a distance, the ocean surface has a low albedo, as do most forests, whereas desert areas have some of the highest albedos among landforms. Most land areas are in a range of 0.1 to 0.4. The average albedo of Earth is about 0.3 and this is far higher than for the ocean primarily because of the contribution of clouds. Earths surface albedo is regularly estimated via Earth observation satellite sensors such as NASAs MODIS instruments on board the Terra, thereby, the BRDF allows to translate observations of reflectance into albedo. Earths average surface temperature due to its albedo and the effect is currently about 15 °C. If Earth were frozen entirely, the temperature of the planet would drop below −40 °C. If only the land masses became covered by glaciers, the mean temperature of the planet would drop to about 0 °C. In contrast, if the entire Earth was covered by water — a so-called aquaplanet — the average temperature on the planet would rise to almost 27 °C, hence, the actual albedo α can then be given as, α = α ¯ + D α ¯ ¯. Directional-hemispherical reflectance is sometimes referred to as black-sky albedo and bi-hemispherical reflectance as white-sky albedo and these terms are important because they allow the albedo to be calculated for any given illumination conditions from a knowledge of the intrinsic properties of the surface. The albedos of planets, satellites and asteroids can be used to infer much about their properties, the study of albedos, their dependence on wavelength, lighting angle, and variation in time comprises a major part of the astronomical field of photometry
13.
Rosetta (spacecraft)
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Rosetta was a space probe built by the European Space Agency launched on 2 March 2004. Along with Philae, its lander module, Rosetta performed a study of comet 67P/Churyumov–Gerasimenko. During its journey to the comet, the spacecraft flew by Mars and it was launched as the third cornerstone mission of the ESAs Horizon 2000 programme, after SOHO / Cluster and XMM-Newton. On 6 August 2014, the reached the comet and performed a series of manoeuvres to eventually orbit the comet at distances of 30 to 10 kilometres. On 12 November, its lander module Philae performed the first successful landing on a comet, communications with Philae were briefly restored in June and July 2015, but due to diminishing solar power, Rosettas communications module with the lander was turned off on 27 July 2016. On 30 September 2016, the Rosetta spacecraft ended its mission by hard-landing on the comet in its Maat region, the probe is named after the Rosetta Stone, a stele of Egyptian origin featuring a decree in three scripts. The lander is named after the Philae obelisk, which bears a bilingual Greek and it was one of ESAs Horizon 2000 cornerstone missions. The spacecraft consisted of the Rosetta orbiter, which featured 12 instruments, the Rosetta mission orbited Comet Churyumov–Gerasimenko for 17 months and was designed to complete the most detailed study of a comet ever attempted. The spacecraft was controlled from the European Space Operations Centre, in Darmstadt and it has been estimated that in the decade preceding 2014, some 2,000 people assisted in the mission in some capacity. In 2007, Rosetta made a Mars gravity assist on its way to Comet Churyumov–Gerasimenko, the spacecraft also performed two asteroid flybys. The craft completed its flyby of asteroid 2867 Šteins in September 2008, later, on 20 January 2014, Rosetta was taken out of a 31-month hibernation mode as it approached Comet Churyumov–Gerasimenko. Rosettas Philae lander successfully made the first soft landing on a comet nucleus when it touched down on Comet Churyumov–Gerasimenko on 12 November 2014. On 5 September 2016, ESA announced that the lander was discovered by the narrow-angle camera aboard Rosetta as the made a low,2.7 km pass over the comet. The lander sits on its side wedged into a crevice of the comet. During the 1986 approach of Halleys Comet, international space probes were sent to explore the comet, after the probes returned valuable scientific information, it became obvious that follow-ons were needed that would shed more light on cometary composition and answer new questions. Both ESA and NASA started cooperatively developing new probes, the NASA project was the Comet Rendezvous Asteroid Flyby mission. The ESA project was the follow-on Comet Nucleus Sample Return mission, both missions were to share the Mariner Mark II spacecraft design, thus minimising costs. In 1992, after NASA cancelled CRAF due to budgetary limitations, after the spacecraft launch, Gerhard Schwehm was named mission manager, he retired in March 2014
14.
Philae (spacecraft)
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On 12 November 2014, Philae touched down on the comet, but it bounced when its anchoring harpoons failed to deploy and a thruster designed to hold the probe to the surface did not fire. Despite the landing problems, the probes instruments obtained the first images from a comets surface, several of the instruments on Philae made the first direct analysis of a comet, sending back data that will be analysed to determine the composition of the surface. On 15 November 2014 Philae entered safe mode, or hibernation, after its batteries ran down due to reduced sunlight, mission controllers hoped that additional sunlight on the solar panels might be sufficient to reboot the lander. Philae communicated sporadically with Rosetta from 13 June to 9 July 2015, the landers location was identified to within a few tens of metres, but it was not seen. Knowledge of its location will help in interpretation of the images it had sent. On 30 September 2016, the Rosetta spacecraft ended its mission by landing in the comets Maat region, the lander is named after the Philae obelisk, which bears a bilingual inscription and was used along with the Rosetta Stone to decipher Egyptian hieroglyphs. Philae is monitored and operated from DLRs Lander Control Center in Cologne, Philaes mission was to land successfully on the surface of a comet, attach itself, and transmit data about the comets composition. The Rosetta spacecraft and Philae lander were launched on an Ariane 5G+ rocket from French Guiana on 2 March 2004,07,17 UTC, unlike the Deep Impact probe, which by design struck comet Tempel 1s nucleus on 4 July 2005, Philae is not an impactor. Some of the instruments on the lander were used for the first time as autonomous systems during the Mars flyby on 25 February 2007. CIVA, one of the systems, returned some images while the Rosetta instruments were powered down. Most of the other instruments need contact with the surface for analysis, an optimistic estimate of mission length following touchdown was four to five months. In particular, surface and sub-surface samples will be acquired and sequentially analyzed by a suite of instruments, measurements will be performed primarily during descent and along the first five days following touch-down. Philae remained attached to the Rosetta spacecraft after rendezvousing with Churyumov–Gerasimenko on 6 August 2014, on 15 September 2014, ESA announced Site J on the smaller lobe of the comet as the landers destination. Following an ESA public contest in October 2014, Site J was renamed Agilkia in honour of Agilkia Island, a series of four Go/NoGo checks were performed on 11–12 November 2014. One of the tests before detachment from Rosetta showed that the landers cold-gas thruster was not working correctly. Philae detached from Rosetta on 12 November 2014 at 08,35 UTC SCET, Philaes landing signal was received by Earth communication stations at 16,03 UTC after a 28-minute delay. Unknown to mission scientists at that time, the lander had bounced and it began performing scientific measurements while slowly moving away from the comet and coming back down, confusing the science team. Further analysis showed that it bounced twice, Philaes first contact with the comet occurred at 15,34,04 UTC SCET
15.
Planetesimal
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Planetesimals /plænᵻˈtɛsᵻməlz/ are solid objects thought to exist in protoplanetary disks and in debris disks. When the bodies reach sizes of one kilometer, then they can attract each other directly through their mutual gravity. This is how planetesimals are often defined, bodies that are smaller than planetesimals must rely on Brownian motion or turbulent motions in the gas to cause the collisions that can lead to sticking. It is generally thought that about 3, a few planetesimals may have been captured as moons, such as Phobos and Deimos and many of the small high-inclination moons of the giant planets. Planetesimals that have survived to the current day are valuable to science because they contain information about the formation of the Solar System, although their exteriors are subjected to intense solar radiation that can alter their chemistry, their interiors contain pristine material essentially untouched since the planetesimal was formed. This makes each planetesimal a time capsule, and their composition might reveal the conditions in the Solar Nebula from which our planetary system was formed, the word planetesimal comes from the mathematical concept infinitesimal and literally means an ultimately small fraction of a planet. This corresponds to objects larger than approximately 1 km in the solar nebula, bodies large enough not only to keep together by gravitation but to change the path of approaching rocks over distances of several radii start to grow faster. These bodies, larger than 100 km to 1000 km, are called embryos or protoplanets, in other words, some planetesimals became other types of body once planetary formation had finished, and may be referred to by either or both names. The above definition is not endorsed by the International Astronomical Union, there is also no exact dividing line between a planetesimal and protoplanet. Discovering the Essential Universe by Neil F. Comins Linda T. Elkins-Tanton, planetesimals - Early Differentiation and Consequences for Planets. Cambridge University Press, Cambridge 2017, ISBN9781107118485
16.
Electron
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The electron is a subatomic particle, symbol e− or β−, with a negative elementary electric charge. Electrons belong to the first generation of the lepton particle family, the electron has a mass that is approximately 1/1836 that of the proton. Quantum mechanical properties of the include a intrinsic angular momentum of a half-integer value, expressed in units of the reduced Planck constant. As it is a fermion, no two electrons can occupy the same state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of particles and waves, they can collide with other particles and can be diffracted like light. Since an electron has charge, it has an electric field. Electromagnetic fields produced from other sources will affect the motion of an electron according to the Lorentz force law, electrons radiate or absorb energy in the form of photons when they are accelerated. Laboratory instruments are capable of trapping individual electrons as well as electron plasma by the use of electromagnetic fields, special telescopes can detect electron plasma in outer space. Electrons are involved in applications such as electronics, welding, cathode ray tubes, electron microscopes, radiation therapy, lasers, gaseous ionization detectors. Interactions involving electrons with other particles are of interest in fields such as chemistry. The Coulomb force interaction between the positive protons within atomic nuclei and the negative electrons without, allows the composition of the two known as atoms, ionization or differences in the proportions of negative electrons versus positive nuclei changes the binding energy of an atomic system. The exchange or sharing of the electrons between two or more atoms is the cause of chemical bonding. In 1838, British natural philosopher Richard Laming first hypothesized the concept of a quantity of electric charge to explain the chemical properties of atoms. Irish physicist George Johnstone Stoney named this charge electron in 1891, electrons can also participate in nuclear reactions, such as nucleosynthesis in stars, where they are known as beta particles. Electrons can be created through beta decay of isotopes and in high-energy collisions. The antiparticle of the electron is called the positron, it is identical to the electron except that it carries electrical, when an electron collides with a positron, both particles can be totally annihilated, producing gamma ray photons. The ancient Greeks noticed that amber attracted small objects when rubbed with fur, along with lightning, this phenomenon is one of humanitys earliest recorded experiences with electricity. In his 1600 treatise De Magnete, the English scientist William Gilbert coined the New Latin term electricus, both electric and electricity are derived from the Latin ēlectrum, which came from the Greek word for amber, ἤλεκτρον
17.
Photoionization
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Photoionization is the physical process in which an ion is formed from the interaction of a photon with an atom or molecule. Not every photon which encounters an atom or ion will photoionize it, the probability of photoionization is related to the photoionization cross-section, which depends on the energy of the photon and the target being considered. For photon energies below the threshold, the photoionization cross-section is near zero. But with the development of pulsed lasers it has become possible to create extremely intense, at even higher intensities, non-perturbative phenomena such as barrier suppression ionization and rescattering ionization are observed. Several photons of energy below the threshold may actually combine their energies to ionize an atom. This probability decreases rapidly with the number of required, but the development of very intense. In the perturbative regime, the probability of absorbing N photons depends on the laser-light intensity I as IN, for higher intensities, this dependence becomes invalid due to the then occurring AC Stark effect. Resonance-enhanced multiphoton ionization is a technique applied to the spectroscopy of atoms, above threshold ionization is an extension of multi-photon ionization where even more photons are absorbed than actually would be necessary to ionize the atom. The excess energy gives the released electron higher kinetic energy than the case of just-above threshold ionization. The electrons released from the target will have approximately an integer number of photon-energies more kinetic energy, then, the electron can tunnel through or for larger distortions even overcome this barrier. These phenomena are called tunnel ionization and over-the-barrier ionization, respectively
18.
Water
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Water is a transparent and nearly colorless chemical substance that is the main constituent of Earths streams, lakes, and oceans, and the fluids of most living organisms. Its chemical formula is H2O, meaning that its molecule contains one oxygen, Water strictly refers to the liquid state of that substance, that prevails at standard ambient temperature and pressure, but it often refers also to its solid state or its gaseous state. It also occurs in nature as snow, glaciers, ice packs and icebergs, clouds, fog, dew, aquifers, Water covers 71% of the Earths surface. It is vital for all forms of life. Only 2. 5% of this water is freshwater, and 98. 8% of that water is in ice and groundwater. Less than 0. 3% of all freshwater is in rivers, lakes, and the atmosphere, a greater quantity of water is found in the earths interior. Water on Earth moves continually through the cycle of evaporation and transpiration, condensation, precipitation. Evaporation and transpiration contribute to the precipitation over land, large amounts of water are also chemically combined or adsorbed in hydrated minerals. Safe drinking water is essential to humans and other even though it provides no calories or organic nutrients. There is a correlation between access to safe water and gross domestic product per capita. However, some observers have estimated that by 2025 more than half of the population will be facing water-based vulnerability. A report, issued in November 2009, suggests that by 2030, in developing regions of the world. Water plays an important role in the world economy, approximately 70% of the freshwater used by humans goes to agriculture. Fishing in salt and fresh water bodies is a source of food for many parts of the world. Much of long-distance trade of commodities and manufactured products is transported by boats through seas, rivers, lakes, large quantities of water, ice, and steam are used for cooling and heating, in industry and homes. Water is an excellent solvent for a variety of chemical substances, as such it is widely used in industrial processes. Water is also central to many sports and other forms of entertainment, such as swimming, pleasure boating, boat racing, surfing, sport fishing, Water is a liquid at the temperatures and pressures that are most adequate for life. Specifically, at atmospheric pressure of 1 bar, water is a liquid between the temperatures of 273.15 K and 373.15 K
19.
Molecule
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A molecule is an electrically neutral group of two or more atoms held together by chemical bonds. Molecules are distinguished from ions by their lack of electrical charge, however, in quantum physics, organic chemistry, and biochemistry, the term molecule is often used less strictly, also being applied to polyatomic ions. In the kinetic theory of gases, the molecule is often used for any gaseous particle regardless of its composition. According to this definition, noble gas atoms are considered molecules as they are in fact monoatomic molecules. A molecule may be homonuclear, that is, it consists of atoms of one element, as with oxygen, or it may be heteronuclear. Atoms and complexes connected by non-covalent interactions, such as hydrogen bonds or ionic bonds, are not considered single molecules. Molecules as components of matter are common in organic substances and they also make up most of the oceans and atmosphere. Also, no typical molecule can be defined for ionic crystals and covalent crystals, the theme of repeated unit-cellular-structure also holds for most condensed phases with metallic bonding, which means that solid metals are also not made of molecules. In glasses, atoms may also be together by chemical bonds with no presence of any definable molecule. The science of molecules is called molecular chemistry or molecular physics, in practice, however, this distinction is vague. In molecular sciences, a molecule consists of a system composed of two or more atoms. Polyatomic ions may sometimes be thought of as electrically charged molecules. The term unstable molecule is used for very reactive species, i. e, according to Merriam-Webster and the Online Etymology Dictionary, the word molecule derives from the Latin moles or small unit of mass. Molecule – extremely minute particle, from French molécule, from New Latin molecula, diminutive of Latin moles mass, a vague meaning at first, the vogue for the word can be traced to the philosophy of Descartes. The definition of the molecule has evolved as knowledge of the structure of molecules has increased, earlier definitions were less precise, defining molecules as the smallest particles of pure chemical substances that still retain their composition and chemical properties. Molecules are held together by covalent bonding or ionic bonding. Several types of non-metal elements exist only as molecules in the environment, for example, hydrogen only exists as hydrogen molecule. A molecule of a compound is made out of two or more elements, a covalent bond is a chemical bond that involves the sharing of electron pairs between atoms
20.
Sunlight
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Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is filtered through Earths atmosphere, and is obvious as daylight when the Sun is above the horizon, when the direct solar radiation is not blocked by clouds, it is experienced as sunshine, a combination of bright light and radiant heat. When it is blocked by clouds or reflects off other objects, the World Meteorological Organization uses the term sunshine duration to mean the cumulative time during which an area receives direct irradiance from the Sun of at least 120 watts per square meter. Other sources indicate an Average over the earth of 164 Watts per square meter over a 24 hour day. The ultraviolet radiation in sunlight has both positive and negative effects, as it is both a principal source of vitamin D3 and a mutagen. Sunlight takes about 8.3 minutes to reach Earth from the surface of the Sun. A photon starting at the center of the Sun and changing every time it encounters a charged particle would take between 10,000 and 170,000 years to get to the surface. Researchers may record sunlight using a sunshine recorder, pyranometer, or pyrheliometer, to calculate the amount of sunlight reaching the ground, both Earths elliptical orbit and the attenuation by Earths atmosphere have to be taken into account. In this formula dn–3 is used, because in modern times Earths perihelion, the closest approach to the Sun and, therefore, the value of 0.033412 is determined knowing that the ratio between the perihelion squared and the aphelion squared should be approximately 0.935338. The solar illuminance constant, is equal to 128×103 lx, the atmospheric extinction brings the number of lux down to around 100000. The total amount of energy received at ground level from the Sun at the zenith depends on the distance to the Sun and it is about 3. 3% higher than average in January and 3. 3% lower in July. In terms of energy, sunlight at Earths surface is around 52 to 55 percent infrared,42 to 43 percent visible, and 3 to 5 percent ultraviolet. At the top of the atmosphere, sunlight is about 30% more intense, having about 8% ultraviolet, direct sunlight has a luminous efficacy of about 93 lumens per watt of radiant flux. This is higher than the efficacy of most artificial lighting, which means using sunlight for illumination heats up a less than using most forms of artificial lighting. Multiplying the figure of 1050 watts per square metre by 93 lumens per watt indicates that bright sunlight provides an illuminance of approximately 98000 lux on a surface at sea level. The illumination of a surface will be considerably less than this if the Sun is not very high in the sky. Averaged over a day, the highest amount of sunlight on a horizontal surface occurs in January at the South Pole, dividing the irradiance of 1050 W/m2 by the size of the suns disk in steradians gives an average radiance of 15.4 MW per square metre per steradian. Multiplying this by π gives a limit to the irradiance which can be focused on a surface using mirrors,48.5 MW/m2
21.
Photon
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A photon is an elementary particle, the quantum of the electromagnetic field including electromagnetic radiation such as light, and the force carrier for the electromagnetic force. The photon has zero rest mass and is moving at the speed of light. Like all elementary particles, photons are currently best explained by quantum mechanics and exhibit wave–particle duality, exhibiting properties of both waves and particles. For example, a photon may be refracted by a lens and exhibit wave interference with itself. The quanta in a light wave cannot be spatially localized, some defined physical parameters of a photon are listed. The modern concept of the photon was developed gradually by Albert Einstein in the early 20th century to explain experimental observations that did not fit the classical model of light. The benefit of the model was that it accounted for the frequency dependence of lights energy. The photon model accounted for observations, including the properties of black-body radiation. In that model, light was described by Maxwells equations, in 1926 the optical physicist Frithiof Wolfers and the chemist Gilbert N. Lewis coined the name photon for these particles. After Arthur H. Compton won the Nobel Prize in 1927 for his studies, most scientists accepted that light quanta have an independent existence. In the Standard Model of particle physics, photons and other particles are described as a necessary consequence of physical laws having a certain symmetry at every point in spacetime. The intrinsic properties of particles, such as charge, mass and it has been applied to photochemistry, high-resolution microscopy, and measurements of molecular distances. Recently, photons have been studied as elements of quantum computers, in 1900, the German physicist Max Planck was studying black-body radiation and suggested that the energy carried by electromagnetic waves could only be released in packets of energy. In his 1901 article in Annalen der Physik he called these packets energy elements, the word quanta was used before 1900 to mean particles or amounts of different quantities, including electricity. In 1905, Albert Einstein suggested that waves could only exist as discrete wave-packets. He called such a wave-packet the light quantum, the name photon derives from the Greek word for light, φῶς. Arthur Compton used photon in 1928, referring to Gilbert N. Lewis, the name was suggested initially as a unit related to the illumination of the eye and the resulting sensation of light and was used later in a physiological context. Although Wolferss and Lewiss theories were contradicted by many experiments and never accepted, in physics, a photon is usually denoted by the symbol γ
22.
Spacecraft
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A spacecraft is a vehicle, or machine designed to fly in outer space. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, space colonization, planetary exploration, on a sub-orbital spaceflight, a spacecraft enters space and then returns to the surface, without having gone into an orbit. For orbital spaceflights, spacecraft enter closed orbits around the Earth or around other celestial bodies, robotic spacecraft used to support scientific research are space probes. Robotic spacecraft that remain in orbit around a body are artificial satellites. Only a handful of interstellar probes, such as Pioneer 10 and 11, Voyager 1 and 2, orbital spacecraft may be recoverable or not. By method of reentry to Earth they may be divided in non-winged space capsules, Sputnik 1 was the first artificial satellite. It was launched into an elliptical low Earth orbit by the Soviet Union on 4 October 1957, the launch ushered in new political, military, technological, and scientific developments, while the Sputnik launch was a single event, it marked the start of the Space Age. Apart from its value as a technological first, Sputnik 1 also helped to identify the upper atmospheric layers density and it also provided data on radio-signal distribution in the ionosphere. Pressurized nitrogen in the satellites false body provided the first opportunity for meteoroid detection, Sputnik 1 was launched during the International Geophysical Year from Site No. 1/5, at the 5th Tyuratam range, in Kazakh SSR. The satellite travelled at 29,000 kilometers per hour, taking 96.2 minutes to complete an orbit and this altitude is called the Kármán line. In particular, in the 1940s there were several test launches of the V-2 rocket, as of 2016, only three nations have flown manned spacecraft, USSR/Russia, USA, and China. The first manned spacecraft was Vostok 1, which carried Soviet cosmonaut Yuri Gagarin into space in 1961, there were five other manned missions which used a Vostok spacecraft. The second manned spacecraft was named Freedom 7, and it performed a sub-orbital spaceflight in 1961 carrying American astronaut Alan Shepard to an altitude of just over 187 kilometers, there were five other manned missions using Mercury spacecraft. Other Soviet manned spacecraft include the Voskhod, Soyuz, flown unmanned as Zond/L1, L3, TKS, China developed, but did not fly Shuguang, and is currently using Shenzhou. Except for the shuttle, all of the recoverable manned orbital spacecraft were space capsules. Manned space capsules The International Space Station, manned since November 2000, is a joint venture between Russia, the United States, Canada and several other countries, some reusable vehicles have been designed only for manned spaceflight, and these are often called spaceplanes. The first example of such was the North American X-15 spaceplane, the first reusable spacecraft, the X-15, was air-launched on a suborbital trajectory on July 19,1963. The first partially reusable spacecraft, a winged non-capsule, the Space Shuttle, was launched by the USA on the 20th anniversary of Yuri Gagarins flight
23.
Organic compound
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An organic compound is virtually any chemical compound that contains carbon, although a consensus definition remains elusive and likely arbitrary. Organic compounds are rare terrestrially, but of importance because all known life is based on organic compounds. The most basic petrochemicals are considered the building blocks of organic chemistry, for historical reasons discussed below, a few types of carbon-containing compounds, such as carbides, carbonates, simple oxides of carbon, and cyanides are considered inorganic. The distinction between organic and inorganic compounds, while useful in organizing the vast subject of chemistry. Organic chemistry is the science concerned with all aspects of organic compounds, Organic synthesis is the methodology of their preparation. The word organic is historical, dating to the 1st century, for many centuries, Western alchemists believed in vitalism. This is the theory that certain compounds could be synthesized only from their classical elements—earth, water, air, vitalism taught that these organic compounds were fundamentally different from the inorganic compounds that could be obtained from the elements by chemical manipulation. Vitalism survived for a while even after the rise of modern atomic theory and it first came under question in 1824, when Friedrich Wöhler synthesized oxalic acid, a compound known to occur only in living organisms, from cyanogen. A more decisive experiment was Wöhlers 1828 synthesis of urea from the inorganic salts potassium cyanate, urea had long been considered an organic compound, as it was known to occur only in the urine of living organisms. Wöhlers experiments were followed by others, in which increasingly complex organic substances were produced from inorganic ones without the involvement of any living organism. Even though vitalism has been discredited, scientific nomenclature retains the distinction between organic and inorganic compounds, still, even the broadest definition requires excluding alloys that contain carbon, including steel. The C-H definition excludes compounds that are considered organic, neither urea nor oxalic acid is organic by this definition, yet they were two key compounds in the vitalism debate. The IUPAC Blue Book on organic nomenclature specifically mentions urea and oxalic acid, other compounds lacking C-H bonds but traditionally considered organic include benzenehexol, mesoxalic acid, and carbon tetrachloride. Mellitic acid, which contains no C-H bonds, is considered an organic substance in Martian soil. The C-H bond-only rule also leads to somewhat arbitrary divisions in sets of carbon-fluorine compounds, for example, CF4 would be considered by this rule to be inorganic, whereas CF3H would be organic. Organic compounds may be classified in a variety of ways, one major distinction is between natural and synthetic compounds. Another distinction, based on the size of organic compounds, distinguishes between small molecules and polymers, natural compounds refer to those that are produced by plants or animals. Many of these are extracted from natural sources because they would be more expensive to produce artificially
24.
Acetamide
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Acetamide is an organic compound with the formula CH3CONH2. It is the simplest amide derived from acetic acid and it finds some use as a plasticizer and as an industrial solvent. The related compound N, N-dimethylacetamide is more used. This finding is significant because acetamide has an amide bond. This finding lends support to the theory that molecules that can lead to life can form in space. - were seen for the first time on a comet, in addition, acetamide is found infrequently on burning coal dumps, as a mineral of the same name. International Chemical Safety Card 0233 Acetamide
25.
Methyl isocyanate
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Methyl isocyanate is an organic compound with the molecular formula CH3NCO. Synonyms are isocyanatomethane, methyl carbylamine, and MIC, Methyl isocyanate is an intermediate chemical in the production of carbamate pesticides. It has also used in the production of rubbers and adhesives. As a highly toxic and irritating material, it is hazardous to human health. It was the principal toxicant involved in the Bhopal disaster, which killed nearly 2,259 people initially and officially 3,787 people in total, Methyl isocyanate is a colorless, lachrymatory, flammable liquid. It is soluble in water to 6–10 parts per 100 parts, Methyl isocyanate is usually manufactured by the reaction of monomethylamine and phosgene. For large scale production, it is advantageous to combine these reactants at higher temperature in the gas phase. A mixture of methyl isocyanate and two moles of hydrogen chloride is formed, but N-methylcarbamoyl chloride forms as the mixture is condensed, leaving one mole of hydrogen chloride as a gas. The methyl isocyanate is obtained by treating the MCC with an amine, such as N, N-dimethylaniline. Methyl isocyanate is also manufactured from N-methylformamide and air, in the latter process, it is immediately consumed in a closed-loop process to make methomyl. Other manufacturing methods have been reported, Methyl isocyanate reacts readily with many substances that contain N-H or O-H groups. If MIC is in excess,1,3, 5-trimethylbiuret is formed along with carbon dioxide, alcohols and phenols, which contain an O-H group, react slowly with MIC, but the reaction can be catalyzed by trialkylamines or dialkyltin dicarboxylate. Oximes, hydroxylamines, and enols also react with MIC to form methylcarbamates and these reactions produce the products described below. Ammonia, primary, and secondary amines rapidly react with MIC to form substituted ureas, other N-H compounds, such as amides and ureas, react much more slowly with MIC. It also reacts with itself to form a trimer or higher molecular weight polymers, since the formation of the MIC trimer is exothermic, the reaction can lead to violent boiling of the MIC. The high-molecular-weight polymer hydrolyzes in hot water to form the trimethyl isocyanurate, since catalytic metal salts can be formed from impurities in commercial grade MIC and steel, this product must not be stored in steel drums or tanks. Methyl isocyanate is a chemical in the production of carbamate pesticides. It has also used in the production of rubbers and adhesives
26.
Propionaldehyde
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Propionaldehyde or propanal is the organic compound with the formula CH3CH2CHO. It is a saturated 3-carbon aldehyde and is an isomer of acetone. It is a liquid with a slightly irritating, fruity odor. Propionaldehyde may also be prepared by oxidizing 1-propanol with a mixture of sulfuric acid, the reflux condenser contains water heated at 60 °C, which condenses unreacted propanol, but allows propionaldehyde to pass. The propionaldehyde vapor is condensed into a suitable receiver. In this arrangement, any propionaldehyde formed is immediately removed from the reactor and it is principally used as a precursor to trimethylolethane through a condensation reaction with formaldehyde, this triol is an important intermediate in the production of alkyd resins. Other applications include reduction to propanol and oxidation to propionic acid, condensation of propionaldehyde with tert-butylamine gives CH3CH2CH=N-t-Bu, a three-carbon building block used in organic synthesis. Deprotonation of this imine with LDA produces CH3CHLiCH=N-t-Bu, which in turn condenses with aldehydes, astronomers have detected propionaldehyde in the molecular cloud Sagittarius B2 near the center of the Milky Way Galaxy, about 26,000 light years from Earth
27.
Accretion (astrophysics)
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In astrophysics, accretion is the accumulation of particles into a massive object by gravitationally attracting more matter, typically gaseous matter, in an accretion disk. Most astronomical objects, such as galaxies, stars, and planets, are formed by accretion processes, the idea proposed in the 19th century that Earth and the other terrestrial planets formed from meteoric material was developed in a quantitative way in 1969 by Viktor Safronov. He calculated, in detail, the different stages of planet formation. Since then, the theory has been developed using intensive numerical simulations to study planetesimal accumulation. Stars form by the collapse of interstellar gas. Prior to collapse, this gas is mostly in the form of molecular clouds, as the cloud collapses, losing potential energy, it heats up, gaining kinetic energy, and the conservation of angular momentum ensures that the cloud forms a flatted disk—the accretion disk. A few hundred years after the Big Bang, the Universe cooled to the point where atoms could form. As the Universe continued to expand and cool, the atoms lost enough kinetic energy, as further accretion occurred, galaxies formed. Galaxies grow through mergers and smooth gas accretion, accretion also occurs inside galaxies, forming stars. Stars are thought to form inside giant clouds of cold molecular hydrogen—giant molecular clouds of roughly 300,000 M☉ and 65 light-years in diameter, over millions of years, giant molecular clouds are prone to collapse and fragmentation. These fragments then form small, dense cores, which in turn collapse into stars, the cores range in mass from a fraction to several times that of the Sun and are called protostellar nebulae. They possess diameters of 2, 000–20,000 astronomical units, compare it with the particle number density of the air at the sea level—2. 8×1019/cm3. The initial collapse of a solar-mass protostellar nebula takes around 100,000 years, every nebula begins with a certain amount of angular momentum. This core forms the seed of what will become a star, as the collapse continues, conservation of angular momentum dictates that the rotation of the infalling envelope accelerates, which eventually forms a disk. Around this time the protostar begins to fuse deuterium, if the protostar is sufficiently massive, hydrogen fusion follows. Otherwise, if its mass is too low, the object becomes a brown dwarf and this birth of a new star occurs approximately 100,000 years after the collapse begins. Objects at this stage are known as Class I protostars, which are also called young T Tauri stars, evolved protostars, or young stellar objects. By this time, the star has already accreted much of its mass
28.
Helix Nebula
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The Helix Nebula, also known as The Helix, NGC7293, is a large planetary nebula located in the constellation Aquarius. Discovered by Karl Ludwig Harding, probably before 1824, this object is one of the closest to the Earth of all the planetary nebulae. The estimated distance is about 215 parsecs, the Helix Nebula has sometimes been referred to as the Eye of God in pop culture, as well as the Eye of Sauron. The Helix Nebula is an example of a nebula, formed by an intermediate to low-mass star. Gases from the star in the space appear, from our vantage point. The remnant central stellar core, known as a planetary nebula nucleus or PNN, is destined to become a white dwarf star, the observed glow of the central star is so energetic that it causes the previously expelled gases to brightly fluoresce. The Helix Nebula in the constellation of Aquarius lies about 700 light-years away, currently, the age is estimated to be 10600+2300 −1200 years, based solely upon a measured expansion rate of 31 km·s−1. The size of the disk is 8×19 arcmin in diameter, the outer torus is 12×22 arcmin in diameter. We see the outer-most ring as flattened on one due to its colliding with the ambient interstellar medium. Expansion of the planetary nebula structure is estimated to have occurred in the last 6,560 years. Spectroscopically, the outer rings expansion rate is 40 km·s−1, the Helix Nebula was the first planetary nebula discovered to contain cometary knots. Its main ring contains knots of nebulosity, which have now been detected in many nearby planetaries. These knots are highly symmetric and are described as cometary, each centered on a core of neutral molecular gas and containing bright cusps towards the central star. All tails extend away from the PNN in a radial direction, excluding the tails, they are the size of the Solar system, while each of the cusp knots are optically thick due to Lyc photons from the PNN. There are more than 20,000 cometary knots estimated to be in the Helix Nebula, the excitation temperature varies across the Helix nebula
29.
Nebular hypothesis
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The nebular hypothesis is the most widely accepted model in the field of cosmogony to explain the formation and evolution of the Solar System. It suggests that the Solar System formed from nebulous material, the theory was developed by Immanuel Kant and published in his Allgemeine Naturgeschichte und Theorie des Himmels, published in 1755. Originally applied to the Solar System, the process of planetary formation is now thought to be at work throughout the Universe. The widely-accepted modern variant of the hypothesis is the solar nebular disk model or solar nebular model. It offered explanations for a variety of properties of the Solar System, including the circular and coplanar orbits of the planets. Some elements of the hypothesis are echoed in modern theories of planetary formation. According to the hypothesis, stars form in massive and dense clouds of molecular hydrogen—giant molecular clouds. These clouds are gravitationally unstable, and matter coalesces within them to smaller denser clumps, which rotate, collapse. Star formation is a process, which always produces a gaseous protoplanetary disk, proplyd. This may give birth to planets in certain circumstances, which are not well known, thus the formation of planetary systems is thought to be a natural result of star formation. A Sun-like star usually takes approximately 1 million years to form, the protoplanetary disk is an accretion disk that feeds the central star. Initially very hot, the disk later cools in what is known as the T tauri star stage, here, formation of small dust grains made of rocks, the grains eventually may coagulate into kilometer-sized planetesimals. If the disk is massive enough, the runaway accretions begin, near the star, the planetary embryos go through a stage of violent mergers, producing a few terrestrial planets. The last stage takes approximately 100 million to a billion years, the formation of giant planets is a more complicated process. It is thought to occur beyond the frost line, where planetary embryos mainly are made of various types of ice, as a result, they are several times more massive than in the inner part of the protoplanetary disk. What follows after the formation is not completely clear. Some embryos appear to continue to grow and eventually reach 5–10 Earth masses—the threshold value, jupiter- and Saturn-like planets are thought to accumulate the bulk of their mass during only 10,000 years. The accretion stops when the gas is exhausted, the formed planets can migrate over long distances during or after their formation
30.
Oort cloud
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The Oort cloud, sometimes called the Öpik–Oort cloud, is a theoretical cloud of predominantly icy planetesimals believed to surround the Sun to as far as somewhere between 50,000 and 200,000 AU. It is divided into two regions, a disc-shaped inner Oort cloud and a spherical outer Oort cloud, both regions lie beyond the heliosphere and in interstellar space. The Kuiper belt and the disc, the other two reservoirs of trans-Neptunian objects, are less than one thousandth as far from the Sun as the Oort cloud. The outer limit of the Oort cloud defines the boundary of the Solar System. The outer Oort cloud is only bound to the Solar System. These forces occasionally dislodge comets from their orbits within the cloud, based on their orbits, most of the short-period comets may come from the scattered disc, but some may still have originated from the Oort cloud. In 1932, the Estonian astronomer Ernst Öpik postulated that long-period comets originated in a cloud at the outermost edge of the Solar System. The idea was revived by Dutch astronomer Jan Oort as a means to resolve a paradox. Thus, Oort reasoned, a comet could not have formed while in its current orbit, there are two main classes of comet, short-period comets and long-period comets. Ecliptic comets have relatively small orbits, below 10 AU, and follow the ecliptic plane, all long-period comets have very large orbits, on the order of thousands of AU, and appear from every direction in the sky. Oort noted that there was a peak in numbers of comets with aphelia of roughly 20,000 AU. The Oort cloud is thought to occupy a vast space from somewhere between 2,000 and 5,000 AU to as far as 50,000 AU from the Sun, some estimates place the outer edge at between 100,000 and 200,000 AU. The region can be subdivided into a spherical outer Oort cloud of 20, 000–50,000 AU, the outer cloud is only weakly bound to the Sun and supplies the long-period comets to inside the orbit of Neptune. The inner Oort cloud is known as the Hills cloud, named after Jack G. Hills. The Hills cloud explains the existence of the Oort cloud after billions of years. The outer Oort cloud may have trillions of objects larger than 1 km, earlier it was thought to be more massive, but improved knowledge of the size distribution of long-period comets led to lower estimates. The mass of the inner Oort cloud has not been characterized, if analyses of comets are representative of the whole, the vast majority of Oort-cloud objects consist of ices such as water, methane, ethane, carbon monoxide and hydrogen cyanide. The Oort cloud is thought to be a remnant of the protoplanetary disc that formed around the Sun approximately 4.6 billion years ago
31.
Scattered disc
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The scattered disc is a distant circumstellar disc in the Solar System that is sparsely populated by icy minor planets, a subset of the broader family of trans-Neptunian objects. The scattered-disc objects have orbital eccentricities ranging as high as 0.8, inclinations as high as 40° and these extreme orbits are thought to be the result of gravitational scattering by the gas giants, and the objects continue to be subject to perturbation by the planet Neptune. Although the closest scattered-disc objects approach the Sun at about 30–35 AU and this makes scattered objects among the most distant and coldest objects in the Solar System. Eventually, perturbations from the giant planets send such objects towards the Sun, many Oort cloud objects are also thought to have originated in the scattered disc. Detached objects are not sharply distinct from scattered disc objects, during the 1980s, the use of CCD-based cameras in telescopes made it possible to directly produce electronic images that could then be readily digitized and transferred to digital images. Because the CCD captured more light than film and the blinking could now be done at a computer screen. A flood of new discoveries was the result, over a thousand objects were detected between 1992 and 2006. The first scattered-disc object to be recognised as such was 1996 TL66, three more were identified by the same survey in 1999,1999 CV118,1999 CY118, and 1999 CF119. The first object presently classified as an SDO to be discovered was 1995 TL8, as of 2011, over 200 SDOs have been identified, including 2007 UK126,2002 TC302, Eris, Sedna and 2004 VN112. Known trans-Neptunian objects are divided into two subpopulations, the Kuiper belt and the scattered disc. A third reservoir of trans-Neptunian objects, the Oort cloud, has been hypothesized, some researchers further suggest a transitional space between the scattered disc and the inner Oort cloud, populated with detached objects. Those in 3,2 resonances are known as plutinos, because Pluto is the largest member of their group, in contrast to the Kuiper belt, the scattered-disc population can be disturbed by Neptune. Scattered-disc objects come within range of Neptune at their closest approaches. Some objects, like 1999 TD10, blur the distinction and the Minor Planet Center, the MPC also makes a clear distinction between the Kuiper belt and the scattered disc, separating those objects in stable orbits from those in scattered orbits. Another term used is scattered Kuiper-belt object for bodies of the scattered disc and this delineation is inadequate over the age of the Solar System, since bodies trapped in resonances could pass from a scattering phase to a non-scattering phase numerous times. That is, trans-Neptunian objects could travel back and forth between the Kuiper belt and the disc over time. In the a >30 AU region, the region of the Solar System populated by objects with semi-major axes greater than 30 AU, the Minor Planet Center classifies the trans-Neptunian object 90377 Sedna as a scattered-disc object. Under this definition, an object with a greater than 40 AU could be classified as outside the scattered disc
32.
Saturn
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Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with a radius about nine times that of Earth. Although it has only one-eighth the average density of Earth, with its larger volume Saturn is just over 95 times more massive, Saturn is named after the Roman god of agriculture, its astronomical symbol represents the gods sickle. Saturns interior is composed of a core of iron–nickel and rock. This core is surrounded by a layer of metallic hydrogen, an intermediate layer of liquid hydrogen and liquid helium. Saturn has a yellow hue due to ammonia crystals in its upper atmosphere. Saturns magnetic field strength is around one-twentieth of Jupiters, the outer atmosphere is generally bland and lacking in contrast, although long-lived features can appear. Wind speeds on Saturn can reach 1,800 km/h, higher than on Jupiter, sixty-two moons are known to orbit Saturn, of which fifty-three are officially named. This does not include the hundreds of moonlets comprising the rings, Saturn is a gas giant because it is predominantly composed of hydrogen and helium. It lacks a definite surface, though it may have a solid core, Saturns rotation causes it to have the shape of an oblate spheroid, that is, it is flattened at the poles and bulges at its equator. Its equatorial and polar radii differ by almost 10%,60,268 km versus 54,364 km, Jupiter, Uranus, and Neptune, the other giant planets in the Solar System, are also oblate but to a lesser extent. Saturn is the planet of the Solar System that is less dense than water—about 30% less. Although Saturns core is considerably denser than water, the specific density of the planet is 0.69 g/cm3 due to the atmosphere. Jupiter has 318 times the Earths mass, while Saturn is 95 times the mass of the Earth, together, Jupiter and Saturn hold 92% of the total planetary mass in the Solar System. On 8 January 2015, NASA reported determining the center of the planet Saturn, the temperature, pressure, and density inside Saturn all rise steadily toward the core, which causes hydrogen to transition into a metal in the deeper layers. Standard planetary models suggest that the interior of Saturn is similar to that of Jupiter, having a rocky core surrounded by hydrogen. This core is similar in composition to the Earth, but more dense, in 2004, they estimated that the core must be 9–22 times the mass of the Earth, which corresponds to a diameter of about 25,000 km. This is surrounded by a liquid metallic hydrogen layer, followed by a liquid layer of helium-saturated molecular hydrogen that gradually transitions to a gas with increasing altitude
33.
28P/Neujmin
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28P/Neujmin, also known as Neujmin 1, is a large periodic comet in the Solar System. With a perihelion distance of 1. 5AU, this comet does not make close approaches to the Earth, the comet nucleus is estimated to be 21.4 kilometers in diameter with a low albedo of 0.025. Since 28P has such a large nucleus, it will become brighter than the 20th magnitude in early 2019, roughly 2 years before coming to perihelion. When it comes to opposition in May 2020, when it is still 3.5 AU from the Sun, but during the 2021 perihelion passage the comet will be on the opposite side of the Sun as the Earth. The comet is not known for outbursts of activity. Orbital simulation from JPL / Horizons Ephemeris 28P at Kronks Cometography 28P/Neujmin 1
34.
Halley's Comet
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Halleys Comet or Comet Halley, officially designated 1P/Halley, is a short-period comet visible from Earth every 75–76 years. Halley is the only known short-period comet that is visible to the naked eye from Earth. Halley last appeared in the parts of the Solar System in 1986. Halleys returns to the inner Solar System have been observed and recorded by astronomers since at least 240 BC, clear records of the comets appearances were made by Chinese, Babylonian, and medieval European chroniclers, but were not recognized as reappearances of the same object at the time. The comets periodicity was first determined in 1705 by English astronomer Edmond Halley, Comet Halley is commonly pronounced /ˈhæli/, rhyming with valley, or /ˈheɪli/, rhyming with daily. Spellings of Edmond Halleys name during his lifetime included Hailey, Haley, Hayley, Halley, Hawley, Halley was the first comet to be recognized as periodic. Until the Renaissance, the consensus on the nature of comets. This idea was disproved in 1577 by Tycho Brahe, who used parallax measurements to show that comets must lie beyond the Moon, many were still unconvinced that comets orbited the Sun, and assumed instead that they must follow straight paths through the Solar System. In 1687, Sir Isaac Newton published his Philosophiæ Naturalis Principia Mathematica, in which he outlined his laws of gravity and his work on comets was decidedly incomplete. Halley thus concluded that all three comets were, in fact, the same object returning every 76 years, a period that has since been amended to every 75–76 years. After a rough estimate of the perturbations the comet would sustain from the attraction of the planets. Halley died in 1742 before he could observe this himself, Halleys prediction of the comets return proved to be correct, although it was not seen until 25 December 1758, by Johann Georg Palitzsch, a German farmer and amateur astronomer. It did not pass through its perihelion until 13 March 1759 and this effect was computed prior to its return by a team of three French mathematicians, Alexis Clairaut, Joseph Lalande, and Nicole-Reine Lepaute. The confirmation of the return was the first time anything other than planets had been shown to orbit the Sun. It was also one of the earliest successful tests of Newtonian physics, the comet was first named in Halleys honour by French astronomer Nicolas Louis de Lacaille in 1759. Some scholars have proposed that first-century Mesopotamian astronomers already had recognized Halleys Comet as periodic and this theory notes a passage in the Bavli Talmud that refers to a star which appears once in seventy years that makes the captains of the ships err. It was necessary to use ancient Chinese comet observations to constrain their calculations, Halleys orbital period over the last 3 centuries has been between 75–76 years, although it has varied between 74–79 years since 240 BC. Its orbit around the Sun is highly elliptical, with an eccentricity of 0.967
35.
Deep Space 1
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Deep Space 1 was a NASA technology demonstration spacecraft which flew by an asteroid and a comet. It was part of the New Millennium Program, dedicated to testing advanced technologies, launched on 24 October 1998, the Deep Space 1 spacecraft carried out a flyby of asteroid 9969 Braille, which was its primary science target. The mission was extended twice to include an encounter with comet 19P/Borrelly, problems during its initial stages and with its star tracker led to repeated changes in mission configuration. While the flyby of the asteroid was a success, the encounter with the comet retrieved valuable information. Three of twelve technologies on board had to work within a few minutes of separation from the rocket for the mission to continue. The Deep Space series was continued by the Deep Space 2 probes, Deep Space 1 was the first NASA spacecraft to use ion propulsion rather than the traditional chemical-powered rockets. The asteroids in the inner Solar System move in relation to other bodies at a noticeable, predictable speed, thus a spacecraft can determine its relative position by tracking such asteroids across the star background, which appears fixed over such timescales. Two or more asteroids let the spacecraft triangulate its position, two or more positions in time let the spacecraft determine its trajectory, existing spacecraft are tracked by their interactions with the transmitters of the NASA Deep Space Network, in effect an inverse GPS. However, DSN tracking requires many skilled operators, and the DSN is overburdened by its use as a communications network, the use of Autonav reduces mission cost and DSN demands. The Autonav system can also be used in reverse, tracking the position of relative to the spacecraft. This is used to acquire targets for the scientific instruments, the spacecraft is programmed with the targets coarse location. After initial acquisition, Autonav keeps the subject in frame, even commandeering the spacecrafts attitude control, the next spacecraft to use Autonav was Deep Impact. ABLE Engineering developed the technology and built the solar array for DS1, with Entech Inc, who supplied the Fresnel optics. The activity was sponsored by the Ballistic Missile Defense Organization, the SCARLET arrays generated 2.5 kilowatts at 1 AU, with less size and weight than conventional arrays. This lack of a history in space meant that despite the potential savings in propellant mass. Furthermore, unforeseen side effects of ion propulsion might in some way interfere with scientific experiments, such as fields. Therefore, it was a mission of the Deep Space 1 demonstration to show long-duration use of an ion thruster on a scientific mission. The NASA Solar Technology Application Readiness electrostatic ion thruster, developed at NASA Glenn and this is an order of magnitude higher than traditional space propulsion methods, resulting in a mass savings of approximately half
36.
19P/Borrelly
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Comet Borrelly or Borrellys Comet is a periodic comet, which was visited by the spacecraft Deep Space 1 in 2001. The comet last came to perihelion on May 28,2015, the comets nucleus, seen in the image on the right, is particularly notable for being shaped like a bowling pin. The comet was discovered by Alphonse Borrelly during a search for comets at Marseilles. On September 21,2001 the spacecraft Deep Space 1, which was launched to test new equipment in space and it was steered toward the comet during the extended mission of the craft, and presented an unexpected bonus for the mission scientists. Despite the failure of a system that determine its orientation, Deep Space 1 managed to send back to Earth what were, at the time. Http, //jcometobs. web. fc2. com/pcmtn/0019p. htm 19P – Gary W. Kronks Cometography Elements and Ephemeris for 19P/Borrelly – Minor Planet Center
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P/2007 R5
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The periodicity of P/2007 R5 was predicted by Sebastian F. Hönig, a German graduate student and prolific asteroid discoverer, in 2006. The announcement of the new comet was made after the predicted return was confirmed by SOHO. As it passed to within 7.9 million kilometres of the Sun, around.05 AU and this is common behavior for a comet. P/2007 R5 is probably an extinct comet, extinct comets are those that have expelled most of their volatile ice and have little left to form a tail or coma. They are theorized to be common objects amongst the bodies orbiting close to the Sun. P/2007 R5 is probably only 100–200 meters in diameter and it was expected to return in September 2011, and was recovered by B. Discovery credit goes to Terry Lovejoy, Kazimieras Černis, and Bo Zhou, the second periodic comet discovered by SOHO is P/2003 T12. Orbital simulation from JPL / Ephemeris SOHOs first officially periodic comet SOHO Comets
38.
Centaur (minor planet)
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Centaurs are minor planets with a semi-major axis between those of the outer planets. They have unstable orbits that cross or have crossed the orbits of one or more of the giant planets, Centaurs typically behave with characteristics of both asteroids and comets. They are named after the centaurs that were a mixture of horse. It has been estimated there are around 44,000 centaurs in the Solar System with diameters larger than 1 km. The first centaur to be discovered, under the definition of the Jet Propulsion Laboratory, however, they were not recognized as a distinct population until the discovery of 2060 Chiron in 1977. The largest confirmed centaur is 10199 Chariklo, which at 260 km in diameter is as big as a mid-sized main-belt asteroid, however, the lost centaur 1995 SN55 may be somewhat larger. No centaur has been photographed up close, although there is evidence that Saturns moon Phoebe, imaged by the Cassini probe in 2004, in addition, the Hubble Space Telescope has gleaned some information about the surface features of 8405 Asbolus. As of 2008, three centaurs have been found to display comet-like comas, Chiron,60558 Echeclus, and 166P/NEAT, Chiron and Echeclus are therefore classified as both asteroids and comets. Other centaurs, such as 52872 Okyrhoe and 2012 CG, are suspected of having shown comas, any centaur that is perturbed close enough to the Sun is expected to become a comet. The generic definition of a centaur is a body that orbits the Sun between Jupiter and Neptune and crosses the orbits of one or more of the giant planets. Though nowadays the MPC often lists centaurs and scattered disc objects together as a single group, the Jet Propulsion Laboratory similarly defines centaurs as having a semi-major axis, a, between those of Jupiter and Neptune. In contrast, the Deep Ecliptic Survey defines centaurs using a classification scheme. These classifications are based on the change in behavior of the present orbit when extended over 10 million years. The DES defines centaurs as non-resonant objects whose instantaneous perihelia are less than the osculating semi-major axis of Neptune at any time during the simulation and this definition is intended to be synonymous with planet-crossing orbits and to suggest comparatively short lifetimes in the current orbit. The collection The Solar System Beyond Neptune defines objects with an axis between those of Jupiter and Neptune and a Jupiter – Tisserands parameter above 3. The JPL Small-Body Database lists 324 centaurs, there are an additional 65 trans-Neptunian objects with a perihelion closer than the orbit of Uranus. The Committee on Small Body Nomenclature of the International Astronomical Union has not formally weighed in on either side of the debate, thus far, only the binary objects Ceto and Phorcys and Typhon and Echidna have been named according to the new policy. Other objects caught between these differences in classification methods include 944 Hidalgo which was discovered in 1920 and is listed as a centaur in the JPL Small-Body Database
39.
10199 Chariklo
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10199 Chariklo is the largest confirmed centaur. It orbits the Sun between Saturn and Uranus, grazing the orbit of Uranus, on 26 March 2014, astronomers announced the discovery of two rings, around Chariklo by observing a stellar occultation. Making it the first known planet to have rings. Chariklo was discovered by James V. Scotti of the Spacewatch program on February 15,1997, Chariklo is named after the nymph Chariclo, the wife of Chiron and the daughter of Apollo. A photometric study in 2001 was unable to find a definite period of rotation, infrared observations of Chariklo indicate the presence of water ice, which may in fact be located in its rings. Michael Browns website lists it as possibly a dwarf planet with a diameter of 232 km. Chariklo is currently the largest known centaur, with a diameter of about 250 km.2060 Chiron is likely to be the second largest with 220 km. The lost centaur 1995 SN55 may even be larger, with a diameter close to 300 km. The orbit of Chariklo is more stable than those of Nessus, Chiron, Chariklo lies within 0.09 AU of the 4,3 resonance of Uranus and is estimated to have a relatively long orbital half-life of about 10.3 Myr. Orbital simulations of twenty clones of Chariklo suggest that Chariklo will not start to come within 3 AU of Uranus for about thirty thousand years. During the perihelic oppositions of 2003–04, Chariklo had an apparent magnitude of +17.7, as of 2014, Chariklo was 14.8 AU from the Sun. A stellar occultation in 2013 revealed that Chariklo has two rings with radii 396 and 405 km and widths of about 7 km and 3.5 km respectively, the rings are approximately 9 km apart. This makes Chariklo the smallest known object to have rings and these rings are consistent with an edge-on orientation in 2008, which naturally explains Chariklos dimming before 2008 and brightening since. Furthermore, it also explains the gradual disappearance of the water-ice features in Chariklos spectrum before 2008. The existence of a system around a minor planet was unexpected because it had been thought that rings could only be stable around much more massive bodies. Ring systems around minor bodies had not previously been discovered despite the search for them through direct imaging, the team nicknamed the rings Oiapoque and Chuí, after the two rivers that form the northern and southern coastal borders of Brazil. A request for formal names will be submitted to the IAU at a later date,2060 Chiron may have a similar pair of rings. 37th DPS, Albedos, Diameters of Kuiper Belt and Centaur Objects AstDys orbital elements Orbital simulation from JPL / Ephemeris Chariklo Photo Chariklos orbit between Saturn and Uranus
40.
2060 Chiron
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2060 Chiron, also known as 95P/Chiron, is a minor planet in the outer Solar System, orbiting the Sun between Saturn and Uranus. Discovered in 1977 by Charles T. Kowal, it was the member of a new class of objects now known as centaurs—bodies orbiting between the asteroid belt and the Kuiper belt. Besides the four giant planets, Chiron and 10199 Chariklo, also a centaur, are the other bodies in the Solar System known to have rings. Although it was called an asteroid and classified only as a minor planet with the designation 2060 Chiron. Today it is classified as both a planet and a comet, and is accordingly also known by the cometary designation 95P/Chiron. Chiron is named after the centaur Chiron in Greek mythology, michael Brown lists it as possibly a dwarf planet with a measured diameter of 206 km which is near the lower limit for an icy dwarf planet. Chiron was discovered on 1 November 1977 by Charles Kowal from images taken on 18 October at Palomar Observatory and it was given the temporary designation of 1977 UB. It was found near aphelion and at the time of discovery it was the most distant known minor planet, Chiron was even claimed as the tenth planet by the press. Chiron was later found on several images, going back to 1895. It had been at perihelion in 1945 but was not discovered then because there were few searches being made at time. The Lowell Observatorys survey for distant planets would not have gone down faint enough in the 1930s and it was named Chiron in 1979 after Chiron, one of the centaurs, it was suggested that the names of other centaurs be reserved for objects of the same type. Chirons orbit was found to be eccentric, with perihelion just inside the orbit of Saturn. According to the program Solex, Chirons closest approach to Saturn in modern times was around May 720, during this passage Saturns gravity caused Chirons semi-major axis to decrease from 14. 55±0.12 AU to 13.7 AU. It does not come nearly as close to Uranus, Chiron crosses Uranuss orbit where the latter is farther than average from the Sun, Chiron attracted considerable interest because it was the first object discovered in such an orbit, well outside the asteroid belt. Chiron is classified as a centaur, the first of a class of objects orbiting between the outer planets, Chiron is a Saturn–Uranus object because its perihelion lies in Saturns zone of control and its aphelion lies in that of Uranus. Chiron is probably a refugee from the Kuiper belt and will become a short-period comet in about a million years. Chiron came to perihelion in 1996, the visible and near-infrared spectrum of Chiron is neutral, and is similar to that of C-type asteroids and the nucleus of Halleys Comet. The near-infrared spectrum of Chiron shows absence of water ice, the assumed size of an object depends on its absolute magnitude and the albedo
41.
1995 SN55
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1995 SN55, also written as 1995 SN55, is a lost centaur with a perihelion greater than Jupiter and a semi-major axis that may be less than Neptunes. This object could be the largest known centaur, if confirmed to be a centaur,1995 SN55 would be one of the largest centaurs known. Centaurs typically have an albedo of about 0.08, with an absolute magnitude of 6.0, and using an average centaur albedo of 0.08,1995 SN55 could be 295 km in diameter. The two largest known centaurs are 10199 Chariklo and 2060 Chiron,1995 SN55 was about 39 AU from the Sun when it was discovered. It was only observed 14 times over 36 days from September 20,1995, due to this short observation arc, the object has a very poorly known orbit and is considered lost. JPL shows this object having a distance of only 39.1 AU. Orbital simulation from JPL / Ephemeris 1995 SN55 at the JPL Small-Body Database Discovery · Orbit diagram · Orbital elements · Physical parameters
42.
Gram
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The gram is a metric system unit of mass. Originally defined as the weight of a volume of pure water equal to the cube of the hundredth part of a metre. The only unit symbol for gram that is recognised by the International System of Units is g following the numeric value with a space, the SI does not support the use of abbreviations such as gr, gm or Gm. The word gramme was adopted by the French National Convention in its 1795 decree revising the system as replacing the gravet introduced in 1793. Its definition remained that of the weight of a centimetre of water. French gramme was taken from the Late Latin term gramma and this word, ultimately from Greek γράμμα letter had adopted a specialised meaning in Late Antiquity of one twenty-fourth part of an ounce, corresponding to about 1.14 grams. This use of the term is found in the carmen de ponderibus et mensuris composed around 400 AD, the gram was the fundamental unit of mass in the 19th-century centimetre–gram–second system of units. The gram is today the most widely used unit of measurement for non-liquid ingredients in cooking and grocery shopping worldwide. 1 gram =15.4323583529 grains 1 grain =0.06479891 grams 1 avoirdupois ounce =28.349523125 grams 1 troy ounce =31.1034768 grams 100 grams =3.527396195 ounces 1 gram =5 carats 1 gram =8. 1 gram is roughly equal to 1 small paper clip or pen cap, the Japanese 1 yen coin has a mass of one gram. Conversion of units Duella Gold gram Orders of magnitude Gram at Encyclopædia Britannica
43.
Kilogram
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The kilogram or kilogramme is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype of the Kilogram. The avoirdupois pound, used in both the imperial and US customary systems, is defined as exactly 0.45359237 kg, making one kilogram approximately equal to 2.2046 avoirdupois pounds. Other traditional units of weight and mass around the world are also defined in terms of the kilogram, the gram, 1/1000 of a kilogram, was provisionally defined in 1795 as the mass of one cubic centimeter of water at the melting point of ice. The final kilogram, manufactured as a prototype in 1799 and from which the IPK was derived in 1875, had an equal to the mass of 1 dm3 of water at its maximum density. The kilogram is the only SI base unit with an SI prefix as part of its name and it is also the only SI unit that is still directly defined by an artifact rather than a fundamental physical property that can be reproduced in different laboratories. Three other base units and 17 derived units in the SI system are defined relative to the kilogram, only 8 other units do not require the kilogram in their definition, temperature, time and frequency, length, and angle. At its 2011 meeting, the CGPM agreed in principle that the kilogram should be redefined in terms of the Planck constant, the decision was originally deferred until 2014, in 2014 it was deferred again until the next meeting. There are currently several different proposals for the redefinition, these are described in the Proposed Future Definitions section below, the International Prototype Kilogram is rarely used or handled. In the decree of 1795, the term gramme thus replaced gravet, the French spelling was adopted in the United Kingdom when the word was used for the first time in English in 1797, with the spelling kilogram being adopted in the United States. In the United Kingdom both spellings are used, with kilogram having become by far the more common, UK law regulating the units to be used when trading by weight or measure does not prevent the use of either spelling. In the 19th century the French word kilo, a shortening of kilogramme, was imported into the English language where it has used to mean both kilogram and kilometer. In 1935 this was adopted by the IEC as the Giorgi system, now known as MKS system. In 1948 the CGPM commissioned the CIPM to make recommendations for a practical system of units of measurement. This led to the launch of SI in 1960 and the subsequent publication of the SI Brochure, the kilogram is a unit of mass, a property which corresponds to the common perception of how heavy an object is. Mass is a property, that is, it is related to the tendency of an object at rest to remain at rest, or if in motion to remain in motion at a constant velocity. Accordingly, for astronauts in microgravity, no effort is required to hold objects off the cabin floor, they are weightless. However, since objects in microgravity still retain their mass and inertia, the ratio of the force of gravity on the two objects, measured by the scale, is equal to the ratio of their masses. On April 7,1795, the gram was decreed in France to be the weight of a volume of pure water equal to the cube of the hundredth part of the metre
44.
81P/Wild
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Comet 81P/Wild, also known as Wild 2, is a comet named after Swiss astronomer Paul Wild, who discovered it on January 6,1978, using a 40-cm Schmidt telescope at Zimmerwald, Switzerland. For most of its 4.5 billion-year lifetime, Wild 2 probably had a more distant, in September 1974, it passed within one million kilometers of the planet Jupiter, the strong gravitational pull of which perturbed the comets orbit and brought it into the inner Solar System. Its orbital period changed from 43 years to about 6 years, and its perihelion is now about 1.59 astronomical unit. Dimensions,5.5 km ×4.0 km ×3.3 km Density,0.6 g/cm3 Mass,2.3 kg ×1013 NASAs Stardust Mission launched a spacecraft, named Stardust, on February 7,1999. It flew by Wild 2 on January 2,2004, and collected samples from the comets coma. 72 close-up shots were taken of Wild 2 by Stardust and they revealed a surface riddled with flat-bottomed depressions, with sheer walls and other features that range from very small to up to 2 kilometres across. These features are believed to be caused by impact craters or gas vents, during Stardusts flyby, at least 10 gas vents were active. The comet itself has a diameter of 5 kilometres, Stardusts sample return canister was reported to be in excellent condition when it landed in Utah, on January 15,2006. A NASA team analyzed the particle capture cells and removed individual grains of comet and interstellar dust, NASA is collaborating with The Planetary Society who will run a project called Stardust@Home, using volunteers to help locate particles on the Stardust Interstellar Dust Collector. As of 2006, the composition of the dust has contained a range of organic compounds. Indigenous aliphatic hydrocarbons were found with longer lengths than those observed in the diffuse interstellar medium. No hydrous silicates or carbonate minerals were detected, which suggests a lack of processing of Wild 2 dust. Very few pure carbon particles were found in the samples returned, a substantial amount of crystalline silicates such as olivine, anorthite and diopside were found, materials only formed at high temperature. This is consistent with observations of crystalline silicates both in cometary tails and in circumstellar disks at large distances from the star. Possible explanations for this high temperature material at large distances from Sun were summarised before the Stardust sample return mission by van Boekel et al, both in the Solar System and in circumstellar disks crystalline silicates are found at large distances from the star. The origin of these silicates is a matter of debate, the crystals in these regions may have been transported outward through the disk or in an outward-flowing wind. An alternative source of crystalline silicates in the outer disk regions is in situ annealing, a third way to produce crystalline silicates is the collisional destruction of large parent bodies in which secondary processing has taken place. We can use the mineralogy of the dust to derive information about the nature of the primary and/or secondary processes the small-grain population has undergone
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