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1. Orbit – In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet about a star or a natural satellite around a planet. Normally, orbit refers to a regularly repeating path around a body, to a close approximation, planets and satellites follow elliptical orbits, with the central mass being orbited at a focal point of the ellipse, as described by Keplers laws of planetary motion. For ease of calculation, in most situations orbital motion is adequately approximated by Newtonian Mechanics, historically, the apparent motions of the planets were described by European and Arabic philosophers using the idea of celestial spheres. This model posited the existence of perfect moving spheres or rings to which the stars and it assumed the heavens were fixed apart from the motion of the spheres, and was developed without any understanding of gravity. After the planets motions were accurately measured, theoretical mechanisms such as deferent. Originally geocentric it was modified by Copernicus to place the sun at the centre to help simplify the model, the model was further challenged during the 16th century, as comets were observed traversing the spheres. The basis for the understanding of orbits was first formulated by Johannes Kepler whose results are summarised in his three laws of planetary motion. Second, he found that the speed of each planet is not constant, as had previously been thought. Third, Kepler found a relationship between the orbital properties of all the planets orbiting the Sun. For the planets, the cubes of their distances from the Sun are proportional to the squares of their orbital periods. Jupiter and Venus, for example, are respectively about 5.2 and 0.723 AU distant from the Sun, their orbital periods respectively about 11.86 and 0.615 years. The proportionality is seen by the fact that the ratio for Jupiter,5. 23/11.862, is equal to that for Venus,0. 7233/0.6152. Idealised orbits meeting these rules are known as Kepler orbits, isaac Newton demonstrated that Keplers laws were derivable from his theory of gravitation and that, in general, the orbits of bodies subject to gravity were conic sections. Newton showed that, for a pair of bodies, the sizes are in inverse proportion to their masses. Where one body is more massive than the other, it is a convenient approximation to take the center of mass as coinciding with the center of the more massive body. Lagrange developed a new approach to Newtonian mechanics emphasizing energy more than force, in a dramatic vindication of classical mechanics, in 1846 le Verrier was able to predict the position of Neptune based on unexplained perturbations in the orbit of Uranus. This led astronomers to recognize that Newtonian mechanics did not provide the highest accuracy in understanding orbits, in relativity theory, orbits follow geodesic trajectories which are usually approximated very well by the Newtonian predictions but the differences are measurable. Essentially all the evidence that can distinguish between the theories agrees with relativity theory to within experimental measurement accuracy

2. Mars – Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, after Mercury. Named after the Roman god of war, it is referred to as the Red Planet because the iron oxide prevalent on its surface gives it a reddish appearance. Mars is a planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the valleys, deserts, and polar ice caps of Earth. The rotational period and seasonal cycles of Mars are likewise similar to those of Earth, Mars is the site of Olympus Mons, the largest volcano and second-highest known mountain in the Solar System, and of Valles Marineris, one of the largest canyons in the Solar System. The smooth Borealis basin in the northern hemisphere covers 40% of the planet, Mars has two moons, Phobos and Deimos, which are small and irregularly shaped. These may be captured asteroids, similar to 5261 Eureka, a Mars trojan, there are ongoing investigations assessing the past habitability potential of Mars, as well as the possibility of extant life. Future astrobiology missions are planned, including the Mars 2020 and ExoMars rovers, liquid water cannot exist on the surface of Mars due to low atmospheric pressure, which is about  6⁄1000 that of the Earths, except at the lowest elevations for short periods. The two polar ice caps appear to be largely of water. The volume of ice in the south polar ice cap, if melted. On November 22,2016, NASA reported finding a large amount of ice in the Utopia Planitia region of Mars. The volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior, Mars can easily be seen from Earth with the naked eye, as can its reddish coloring. Its apparent magnitude reaches −2.91, which is surpassed only by Jupiter, Venus, the Moon, optical ground-based telescopes are typically limited to resolving features about 300 kilometers across when Earth and Mars are closest because of Earths atmosphere. Mars is approximately half the diameter of Earth with an area only slightly less than the total area of Earths dry land. Mars is less dense than Earth, having about 15% of Earths volume and 11% of Earths mass, the red-orange appearance of the Martian surface is caused by iron oxide, or rust. It can look like butterscotch, other common colors include golden, brown, tan. Like Earth, Mars has differentiated into a metallic core overlaid by less dense materials. Current models of its interior imply a core with a radius of about 1,794 ±65 kilometers, consisting primarily of iron and this iron sulfide core is thought to be twice as rich in lighter elements than Earths. The core is surrounded by a mantle that formed many of the tectonic and volcanic features on the planet

3. Astronomical unit – The astronomical unit is a unit of length, roughly the distance from Earth to the Sun. However, that varies as Earth orbits the Sun, from a maximum to a minimum. Originally conceived as the average of Earths aphelion and perihelion, it is now defined as exactly 149597870700 metres, the astronomical unit is used primarily as a convenient yardstick for measuring distances within the Solar System or around other stars. However, it is also a component in the definition of another unit of astronomical length. A variety of symbols and abbreviations have been in use for the astronomical unit. In a 1976 resolution, the International Astronomical Union used the symbol A for the astronomical unit, in 2006, the International Bureau of Weights and Measures recommended ua as the symbol for the unit. In 2012, the IAU, noting that various symbols are presently in use for the astronomical unit, in the 2014 revision of the SI Brochure, the BIPM used the unit symbol au. In ISO 80000-3, the symbol of the unit is ua. Earths orbit around the Sun is an ellipse, the semi-major axis of this ellipse is defined to be half of the straight line segment that joins the aphelion and perihelion. The centre of the sun lies on this line segment. In addition, it mapped out exactly the largest straight-line distance that Earth traverses over the course of a year, knowing Earths shift and a stars shift enabled the stars distance to be calculated. But all measurements are subject to some degree of error or uncertainty, improvements in precision have always been a key to improving astronomical understanding. Improving measurements were continually checked and cross-checked by means of our understanding of the laws of celestial mechanics, the expected positions and distances of objects at an established time are calculated from these laws, and assembled into a collection of data called an ephemeris. NASAs Jet Propulsion Laboratory provides one of several ephemeris computation services, in 1976, in order to establish a yet more precise measure for the astronomical unit, the IAU formally adopted a new definition. Equivalently, by definition, one AU is the radius of an unperturbed circular Newtonian orbit about the sun of a particle having infinitesimal mass. As with all measurements, these rely on measuring the time taken for photons to be reflected from an object. However, for precision the calculations require adjustment for such as the motions of the probe. In addition, the measurement of the time itself must be translated to a scale that accounts for relativistic time dilation

4. Asteroid – Asteroids are minor planets, especially those of the inner Solar System. The larger ones have also been called planetoids and these terms have historically been applied to any astronomical object orbiting the Sun that did not show the disc of a planet and was not observed to have the characteristics of an active comet. As minor planets in the outer Solar System were discovered and found to have volatile-based surfaces that resemble those of comets, in this article, the term asteroid refers to the minor planets of the inner Solar System including those co-orbital with Jupiter. There are millions of asteroids, many thought to be the remnants of planetesimals. The large majority of known asteroids orbit in the belt between the orbits of Mars and Jupiter, or are co-orbital with Jupiter. However, other orbital families exist with significant populations, including the near-Earth objects, individual asteroids are classified by their characteristic spectra, with the majority falling into three main groups, C-type, M-type, and S-type. These were named after and are identified with carbon-rich, metallic. The size of asteroids varies greatly, some reaching as much as 1000 km across, asteroids are differentiated from comets and meteoroids. In the case of comets, the difference is one of composition, while asteroids are composed of mineral and rock, comets are composed of dust. In addition, asteroids formed closer to the sun, preventing the development of the aforementioned cometary ice, the difference between asteroids and meteoroids is mainly one of size, meteoroids have a diameter of less than one meter, whereas asteroids have a diameter of greater than one meter. Finally, meteoroids can be composed of either cometary or asteroidal materials, only one asteroid,4 Vesta, which has a relatively reflective surface, is normally visible to the naked eye, and this only in very dark skies when it is favorably positioned. Rarely, small asteroids passing close to Earth may be visible to the eye for a short time. As of March 2016, the Minor Planet Center had data on more than 1.3 million objects in the inner and outer Solar System, the United Nations declared June 30 as International Asteroid Day to educate the public about asteroids. The date of International Asteroid Day commemorates the anniversary of the Tunguska asteroid impact over Siberia, the first asteroid to be discovered, Ceres, was found in 1801 by Giuseppe Piazzi, and was originally considered to be a new planet. In the early half of the nineteenth century, the terms asteroid. Asteroid discovery methods have improved over the past two centuries. This task required that hand-drawn sky charts be prepared for all stars in the band down to an agreed-upon limit of faintness. On subsequent nights, the sky would be charted again and any moving object would, hopefully, the expected motion of the missing planet was about 30 seconds of arc per hour, readily discernible by observers

5. Perihelion and aphelion – The perihelion is the point in the orbit of a celestial body where it is nearest to its orbital focus, generally a star. It is the opposite of aphelion, which is the point in the orbit where the body is farthest from its focus. The word perihelion stems from the Ancient Greek words peri, meaning around or surrounding, aphelion derives from the preposition apo, meaning away, off, apart. According to Keplers first law of motion, all planets, comets. Hence, a body has a closest and a farthest point from its parent object, that is, a perihelion. Each extreme is known as an apsis, orbital eccentricity measures the flatness of the orbit. Because of the distance at aphelion, only 93. 55% of the solar radiation from the Sun falls on a given area of land as does at perihelion. However, this fluctuation does not account for the seasons, as it is summer in the northern hemisphere when it is winter in the southern hemisphere and vice versa. Instead, seasons result from the tilt of Earths axis, which is 23.4 degrees away from perpendicular to the plane of Earths orbit around the sun. Winter falls on the hemisphere where sunlight strikes least directly, and summer falls where sunlight strikes most directly, in the northern hemisphere, summer occurs at the same time as aphelion. Despite this, there are larger land masses in the northern hemisphere, consequently, summers are 2.3 °C warmer in the northern hemisphere than in the southern hemisphere under similar conditions. Apsis Ellipse Solstice Dates and times of Earths perihelion and aphelion, 2000–2025 from the United States Naval Observatory

6. Outer-grazer – Outer-grazer and inner-grazer are schemes of Sun Orbits. All six diagrams show the Sun in the middle and a putative planets orbital band, the latter is a ring whose inner radius is the planets perihelion and its outer radius the aphelion. Middle column, top, The minor planets orbit enters the planets orbit from the inside without traversing it — it is an inner-grazer. Middle column, bottom, The minor planets orbit enters the planets from outside without traversing it — it is an outer-grazer, earth grazing fireball, grazes Earths atmosphere rather an orbit

7. Co-orbital configuration – There are several classes of co-orbital objects, depending on their point of libration. The most common and best-known class is the trojan, which librates around one of the two stable Lagrangian points, L4 and L5, 60° ahead of and behind the larger body respectively. Another class is the orbit, in which objects librate around 180° from the larger body. Objects librating around 0° are called quasi-satellites, an exchange orbit occurs when two co-orbital objects are of similar masses and thus exert a non-negligible influence on each other. The objects can exchange semi-major axes or eccentricities when they approach each other, orbital parameters that are used to describe the relation of co-orbital objects are the longitude of the periapsis difference and the mean longitude difference. The longitude of the periapsis is the sum of the longitude and the mean anomaly and the mean longitude is the sum of the longitude of the ascending node. Trojan objects orbit 60° ahead of or behind a massive object. The best known example are the asteroids that orbit ahead of or behind Jupiter around the Sun, trojan objects do not orbit exactly at one of either Lagrangian points, but do remain relatively close to it, appearing to slowly orbit it. In technical terms, they librate around =, the point around which they librate is the same, irrespective of their mass or orbital eccentricity. There are several thousand known trojan minor planets orbiting the Sun, most of these orbit near Jupiters Lagrangian points, the traditional Jupiter trojans. As of 2015 there are also 13 Neptune trojans,7 Mars trojans,1 Uranus trojan and 1 Earth trojan known to exist, the Saturnian system contains two sets of trojan moons. Both Tethys and Dione have two moons, Telesto and Calypso in Tethyss L4 and L5 respectively, and Helene and Polydeuces in Diones L4. Polydeuces is noticeable for its wide libration, it wanders as far as ±30° from its Lagrangian point and ±2% from its orbital radius. A pair of co-orbital exoplanets was proposed to be orbiting the star Kepler-223, the possibility of a trojan planet to Kepler-91b was studied but the conclusion was that the transit-signal was a false-positive. One possibility for the zone is a trojan planet of a giant planet close to its star. Objects in a horseshoe orbit librate around 180° from the primary and their orbits encompass both equilateral Lagrangian points, i. e. L4 and L5. The Saturnian moons Janus and Epimetheus share their orbits, the difference in semi-major axes being less than eithers mean diameter and this means the moon with the smaller semi-major axis will slowly catch up with the other. As it does this, the moons gravitationally tug at each other, increasing the semi-major axis of the moon that has caught up and this reverses their relative positions proportionally to their masses and causes this process to begin anew with the moons roles reversed

8. Near-Earth object – A near-Earth object is any small Solar System body whose orbit brings it into proximity with Earth. By definition, a solar system body is a NEO if its closest approach to the Sun is less than 1.3 astronomical unit and it is now widely accepted that collisions in the past have had a significant role in shaping the geological and biological history of the Earth. NEOs have become of increased interest since the 1980s because of increased awareness of the potential danger some of the asteroids or comets pose, and mitigations are being researched. In January 2016, NASA announced the Planetary Defense Coordination Office to track NEOs larger than 30 to 50 meters in diameter and coordinate an effective threat response, NEAs have orbits that lie partly between 0.983 and 1.3 AU away from the Sun. When a NEA is detected it is submitted to the IAUs Minor Planet Center for cataloging, some NEAs orbits intersect that of Earths so they pose a collision danger. The United States, European Union, and other nations are currently scanning for NEOs in an effort called Spaceguard. In the United States and since 1998, NASA has a mandate to catalogue all NEOs that are at least 1 kilometer wide. In 2006, it was estimated that 20% of the objects had not yet been found. In 2011, largely as a result of NEOWISE, it was estimated that 93% of the NEAs larger than 1 km had been found, as of 5 February 2017, there have been 875 NEAs larger than 1 km discovered, of which 157 are potentially hazardous. The inventory is much less complete for smaller objects, which still have potential for scale, though not global. Potentially hazardous objects are defined based on parameters that measure the objects potential to make threatening close approaches to the Earth. Mostly objects with an Earth minimum orbit intersection distance of 0.05 AU or less, objects that cannot approach closer to the Earth than 0.05 AU, or are smaller than about 150 m in diameter, are not considered PHOs. This makes them a target for exploration. As of 2016, three near-Earth objects have been visited by spacecraft, more recently, a typical frame of reference for looking at NEOs has been through the scientific concept of risk. In this frame, the risk that any near-Earth object poses is typically seen through a lens that is a function of both the culture and the technology of human society, NEOs have been understood differently throughout history. Each time an NEO is observed, a different risk was posed and it is not just a matter of scientific knowledge. Such perception of risk is thus a product of religious belief, philosophic principles, scientific understanding, technological capabilities, and even economical resourcefulness.03 E −0.4 megatonnes. For instance, it gives the rate for bolides of 10 megatonnes or more as 1 per thousand years, however, the authors give a rather large uncertainty, due in part to uncertainties in determining the energies of the atmospheric impacts that they used in their determination

9. Amor asteroid – The Amor asteroids are a group of near-Earth asteroids named after the asteroid 1221 Amor. They approach the orbit of Earth from beyond, but do not cross it, most Amors cross the orbit of Mars. The two moons of Mars, Deimos and Phobos, may be Amor asteroids that were captured by Marss gravity, the most famous member of this group is 433 Eros, which was the first asteroid to be orbited and then landed upon by a human probe. There are three general criteria which an asteroid must meet to be considered a member of the Amor asteroid class, to be considered near, the asteroid must come closer to Earth than to any other major planet. The closest planet to Earth is Venus, which can come as close as 0.27 AU, therefore, an Amor asteroid must come within 0.30 AU of Earths orbit. The asteroids orbit must be outside the orbit of Earth, asteroids that come close to Earth whose orbits are inside Earths orbit are considered Apohele asteroids. The asteroids orbit must not cross Earths orbit, the most commonly used definition of this is that it never orbits closer to the Sun than Earths average distance from the Sun. A more strict definition is that at any point along the asteroids orbit and this takes into consideration the fact that Earths orbit ranges between 0.983 and 1.016 AU from the Sun. It is more difficult to sort out the Amor asteroids from the non-Amor asteroids using this definition, however. These three criteria boil down to a single test for membership, If an asteroid has a perihelion between 1.000 AU and 1.300 AU, it is an Amor asteroid. Any asteroid with this trait is considered an Amor-class asteroid, regardless of its axis, eccentricity, aphelion, inclination, physical properties, orbital stability. An asteroid belongs to the Amor group if, Its orbital period is greater than one year and this is equivalent to saying that its semi-major axis is greater than 1.0 AU. Its orbit does not cross Earths orbit and that is, its lowest point is higher than Earths highest point. It is an object, that is, its perihelion distance q <1.3 AU. In summary, a >1.0 AU and 1.017 AU < q <1.3 AU, there are 6051 Amor asteroids currently known. 960 of them are numbered, and 73 of them are named, Amor asteroids can be partitioned into four subgroups, depending on their average distance from the Sun. The Amor I subgroup consists of Amor asteroids whose semi-major axes are in between Earth and Mars and that is, they have a semi-major axis between 1.000 and 1.523 AU. Less than one fifth of Amor asteroids belong to this subgroup, Amor I asteroids have lower eccentricities than the other subgroups of Amors

10. Asteroid belt – The asteroid belt is the circumstellar disc in the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets, the asteroid belt is also termed the main asteroid belt or main belt to distinguish it from other asteroid populations in the Solar System such as near-Earth asteroids and trojan asteroids. About half the mass of the belt is contained in the four largest asteroids, Ceres, Vesta, Pallas, the total mass of the asteroid belt is approximately 4% that of the Moon, or 22% that of Pluto, and roughly twice that of Plutos moon Charon. Ceres, the belts only dwarf planet, is about 950 km in diameter, whereas Vesta, Pallas. The remaining bodies range down to the size of a dust particle, the asteroid material is so thinly distributed that numerous unmanned spacecraft have traversed it without incident. Nonetheless, collisions between large asteroids do occur, and these can form a family whose members have similar orbital characteristics. Individual asteroids within the belt are categorized by their spectra. The asteroid belt formed from the solar nebula as a group of planetesimals. Planetesimals are the precursors of the protoplanets. Between Mars and Jupiter, however, gravitational perturbations from Jupiter imbued the protoplanets with too much energy for them to accrete into a planet. Collisions became too violent, and instead of fusing together, the planetesimals, as a result,99. 9% of the asteroid belts original mass was lost in the first 100 million years of the Solar Systems history. Some fragments eventually found their way into the inner Solar System, Asteroid orbits continue to be appreciably perturbed whenever their period of revolution about the Sun forms an orbital resonance with Jupiter. At these orbital distances, a Kirkwood gap occurs as they are swept into other orbits. Classes of small Solar System bodies in other regions are the objects, the centaurs, the Kuiper belt objects, the scattered disc objects, the sednoids. On 22 January 2014, ESA scientists reported the detection, for the first definitive time, of water vapor on Ceres, the detection was made by using the far-infrared abilities of the Herschel Space Observatory. The finding was unexpected because comets, not asteroids, are considered to sprout jets. According to one of the scientists, The lines are becoming more and more blurred between comets and asteroids. This pattern, now known as the Titius–Bode law, predicted the semi-major axes of the six planets of the provided one allowed for a gap between the orbits of Mars and Jupiter

11. Hungaria group – The Hungaria family is a group of asteroids in the asteroid belt. The Hungaria asteroids orbit the Sun with an axis between 1.78 and 2.00 astronomical units. They are the innermost dense concentration of asteroids in the Solar System—the near-Earth asteroids are much more sparse—and derive their name from their largest member 434 Hungaria. The Hungaria asteroids typically share the following parameters, Semi-major axis between 1.78 and 2.00 AU Orbital period of approximately 2.5 years Low eccentricity of below 0. For comparison the majority of asteroids are in region of the asteroid belt. Most Hungarias are E-type asteroids, which means they have extremely bright enstatite surfaces, despite their high albedos, none can be seen with binoculars because they are far too small, the largest is only about 11 km in size. They are, however, the smallest asteroids that can regularly be glimpsed with amateur telescopes, the origin of the Hungaria group of asteroids is well known. Interior to this 4,1 resonance, asteroids in low inclination orbits are, unlike those outside the 4,1 Kirkwood gap, strongly influenced by the gravitational field of Mars. This has left a situation where the remaining concentration of asteroids inward of the 4,1 resonance lies at high inclination orbits. However, even at the present time in Solar System history some Hungaria asteroids cross the orbit of Mars and are still in the process of being ejected from the Solar System due to Marss influence. Long-term changes in the orbit of Mars are believed to be a factor in the current removal of Hungaria asteroids. This ultimately leads over millions of years to the formation of the short-lived Amor asteroids, the Hungaria asteroids are thought to be the remains of the hypothetical E-belt asteroid population. E-type asteroid Aubrite 2004 VD1764 Angelina 434 Hungaria 44 Nysa 55 Pandora 2867 Šteins

12. Mars trojan – The Mars trojans are a group of objects that share the orbit of the planet Mars around the Sun. They can be found around the two Lagrangian points 60° ahead of and behind Mars, the origin of the Mars trojans is not well understood. One theory suggests that they were captured in its Lagrangian points as the Solar System was forming, however, spectral studies of the Mars trojans indicate this may not be the case. One explanation for this involves asteroids wandering into the Mars Lagrangian points later in the Solar Systems formation and this is also questionable considering the very low mass of Mars

13. 5261 Eureka – 5261 Eureka is the first Mars trojan discovered. It was discovered by David H. Levy and Henry Holt at Palomar Observatory on June 20,1990 from the Palomar Observatory and it trails Mars at a distance varying by only 0.3 AU during each revolution. Minimum distances from the Earth, Venus, and Jupiter, are 0.5,0.8, long-term numerical integration shows that the orbit is stable. At least five other asteroids in near-1,1 resonances with Mars have been discovered and they are 2001 FR127,2001 FG24,1999 ND43,1998 QH56 and 1998 SD4. The infrared spectrum for 5261 Eureka is typical for an A-type asteroid, a-class asteroids are tinted red in hue, with a moderate albedo. On November 28,2011, a satellite of 5261 Eureka was found. It has yet to be named, and its designation is S/20111. The moon is about 0.46 km in diameter and orbits 2.1 km from Eureka, the satellites existence was announced in September 2014. S. Tabachnik and N. W. Evans, Cartography for Martian Trojans, The Astrophysical Journal 517,1999, pp. L63-L66

14. Albedo – 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

15. Lagrangian point – The Lagrange points mark positions where the combined gravitational pull of the two large masses provides precisely the centrifugal force required to orbit with them. There are five points, labeled L1 to L5, all in the orbital plane of the two large bodies. The first three are on the line connecting the two bodies, the last two, L4 and L5, each form an equilateral triangle with the two large bodies. The two latter points are stable, which implies that objects can orbit around them in a coordinate system tied to the two large bodies. Several planets have satellites near their L4 and L5 points with respect to the Sun, the three collinear Lagrange points were discovered by Leonhard Euler a few years before Lagrange discovered the remaining two. In 1772, Joseph-Louis Lagrange published an Essay on the three-body problem, in the first chapter he considered the general three-body problem. From that, in the chapter, he demonstrated two special constant-pattern solutions, the collinear and the equilateral, for any three masses, with circular orbits. The five Lagrangian points are labeled and defined as follows, The L1 point lies on the line defined by the two large masses M1 and M2, and between them. It is the most intuitively understood of the Lagrangian points, the one where the attraction of M2 partially cancels M1s gravitational attraction. Explanation An object that orbits the Sun more closely than Earth would normally have an orbital period than Earth. If the object is directly between Earth and the Sun, then Earths gravity counteracts some of the Suns pull on the object, the closer to Earth the object is, the greater this effect is. At the L1 point, the period of the object becomes exactly equal to Earths orbital period. L1 is about 1.5 million kilometers from Earth, the L2 point lies on the line through the two large masses, beyond the smaller of the two. Here, the forces of the two large masses balance the centrifugal effect on a body at L2. Explanation On the opposite side of Earth from the Sun, the period of an object would normally be greater than that of Earth. The extra pull of Earths gravity decreases the orbital period of the object, like L1, L2 is about 1.5 million kilometers from Earth. The L3 point lies on the line defined by the two masses, beyond the larger of the two. Explanation L3 in the Sun–Earth system exists on the side of the Sun

16. (311999) 2007 NS2 – 2007 NS2 is an asteroid orbiting near the L5 point of Mars. 2007 NS2 was discovered on July 14,2007, by the Observatorio Astronómico de La Sagra and its orbit is characterized by low eccentricity, moderate inclination and a semi-major axis of 1.52 AU. Upon discovery, it was classified as Mars-crosser by the Minor Planet Center and its orbit is well determined as it is currently based on 87 observations with a data-arc span of 4,800 days. 2007 NS2 has a magnitude of 17.8, which gives a characteristic diameter of 870 m. Jean Meeus suspected that 2007 NS2 was a Mars Trojan, and it was confirmed to be a Mars Trojan numerically in 2012. Recent calculations confirm that it is a stable L5 Mars Trojan asteroid with a period of 1310 years. These values as well as its short-term orbital evolution are similar to those of 5261 Eureka, out of all known Mars Trojans, it currently has the smallest relative semimajor axis,0.000059 AU. Long-term numerical integrations show that its orbit is stable on Gyr time-scales. 5261 Eureka 1999 UJ71998 VF312001 DH472011 SC1912011 SL252011 UN63 Further reading Rodriguez, skiff, B. A. et al.2007 NS2. Schwarz, R. Dvorak, R. Trojan capture by terrestrial planets, doi,10. 1007/s10569-012-9404-4. de la Fuente Marcos, Carlos, de la Fuente Marcos, Raúl. Three new stable L5 Mars Trojans, monthly Notices of the Royal Astronomical Society Letters. Orbital clustering of martian Trojans, An asteroid family in the inner Solar System,2007 NS2 at the JPL Small-Body Database Discovery · Orbit diagram · Orbital elements · Physical parameters 2007 NS2 data at MPC.2007 NS2 data at AstDyS-2

17. (385250) 2001 DH47 – 2001 DH47, also written as 2001 DH47, is a small asteroid orbiting near the L5 point of Mars. 2001 DH47 was discovered on February 1,2001 by the Spacewatch program, observing from Steward Observatory, Kitt Peak and its orbit is characterized by low eccentricity, moderate inclination and a semi-major axis of 1.52 AU. Its orbit is determined as it is currently based on 45 observations with a data-arc span of 3,148 days. It has a magnitude of 19.7 which gives a characteristic diameter of 562 m. It was identified as Mars trojan by H. Scholl, F. Marzari and P. Tricarico in 2005, recent calculations confirm that it is indeed a stable L5 Mars trojan with a libration period of 1365 yr and an amplitude of 11°. These values as well as its short-term orbital evolution are similar to those of 5261 Eureka. Long-term numerical integrations show that its orbit is stable on Gyr time-scales. 5261 Eureka 1999 UJ71998 VF312007 NS22011 SC1912011 SL252011 UN632001 DH47 Ivashchenko,2007, Minor Planet Electronic Circular, 2007-P09. Dynamics of Mars Trojans Scholl, H. Marzari, F. Tricarico, P.2005, Icarus, Volume 175, Issue 2, p. 397–408. Three new stable L5 Mars Trojans de la Fuente Marcos, C. de la Fuente Marcos, R.2013, Monthly Notices of the Royal Astronomical Society, Letters, Vol.432, Issue 1,2001 DH47 data at MPC2001 DH47 data at AstDyS-2. 2001 DH47 at the JPL Small-Body Database Discovery · Orbit diagram · Orbital elements · Physical parameters

18. 2011 SC191 – 2011 SC191, also written as 2011 SC191, is a small asteroid orbiting near the L5 point of Mars. 2011 SC191 was first observed on March 21,2003 by the Near-Earth Asteroid Tracking project at Palomar Observatory using the Samuel Oschin telescope, the object was subsequently lost and re-discovered on October 31,2011 by the Mt. Lemmon Survey. Its orbit is characterized by low eccentricity, moderate inclination and an axis of 1.52 AU. Upon discovery, it was classified as Mars-crosser by the Minor Planet Center and its orbit is well determined as it is currently based on 45 observations with a data-arc span of 3,146 days. 2011 SC191 has a magnitude of 19.3 which gives a characteristic diameter of 600 m. Recent calculations indicate that it is a stable L5 Mars trojan with a period of 1300 yr. These values as well as its short-term orbital evolution are similar to those of 5261 Eureka and its eccentricity oscillates mainly due to secular resonances with the Earth and the oscillation in inclination is likely driven by secular resonances with Jupiter. Long-term numerical integrations show that its orbit is stable on Gyr time-scales. Garradd, G. J. Grauer, A. D. Hill, R. E. Kowalski, R. A. Larson, S. M. McNaught, R. H. Birtwhistle, P.2011, Minor Planet Electronic Circular, 2011-T02. Three new stable L5 Mars Trojans de la Fuente Marcos, C. de la Fuente Marcos, R.2013, Monthly Notices of the Royal Astronomical Society, Letters, Vol.432, Issue 1, pp. 31–35. Orbital clustering of Martian Trojans, An asteroid family in the solar system. Christou, A. A.2013, Icarus, Vol.224, Issue 1,2011 SC191 data at MPC.2011 SC191 data at AstDyS-2. 2011 SC191 at the JPL Small-Body Database Discovery · Orbit diagram · Orbital elements · Physical parameters

19. 2011 UN63 – 2011 UN63, also written as 2011 UN63, is a small minor body orbiting near the L5 point of Mars. 2011 UN63 was first observed on September 27,2009 by the Mt. Lemmon Survey, lost, it was re-discovered on October 21,2011 again by the Mt. Lemmon Survey. 2011 UN63 follows a low eccentricity orbit with an axis of 1.52 AU. This object has moderate orbital inclination and it was classified as Mars-crosser by the Minor Planet Center upon discovery. Its orbit is well determined as it is currently based on 64 observations with a data-arc span of 793 days. This asteroid has a magnitude of 19.7 which gives a characteristic diameter of 560 m. Recent calculations indicate that it is a stable L5 Mars trojan asteroid with a period of 1350 yr. These values as well as its short-term orbital evolution are similar to those of 5261 Eureka or 2011 SC191, long-term numerical integrations show that its orbit is very stable on Gyr time-scales. Orbital clustering of Martian Trojans, An asteroid family in the solar system. Christou, A. A.2013, Icarus, Vol.224, Issue 1,2011 UN63 data at MPC2011 UN63 data at AstDyS-2. 2011 UN63 at the JPL Small-Body Database Discovery · Orbit diagram · Orbital elements · Physical parameters

20. 2011 SL25 – 2011 SL25, also written as 2011 SL25, is a small minor body that has been identified as a L5 Mars trojan candidate. 2011 SL25 was discovered on September 21,2011 at the Alianza S4 Observatory on Cerro Burek in Argentina and it follows a relatively eccentric orbit with a semi-major axis of 1.52 AU. This object has noticeable orbital inclination and its orbit was initially poorly constrained, with only 76 observations over 42 days, but was recovered in January 2014. 2011 SL25 has a magnitude of 19.5 which gives a characteristic diameter of 575 m. Recent calculations indicate that it is a stable L5 Mars Trojan candidate with a period of 1400 yr. Values as well as its short-term orbital evolution are similar to those of 5261 Eureka, long-term numerical integrations show that its orbit is stable on Gyr time-scales. It appears to be stable at least for 4.5 Gyr, Orbital clustering of Martian Trojans, An asteroid family in the inner solar system. Christou, A. A.2013, Icarus, Vol.224, Issue 1,2011 SL25 data at MPC.2011 SL25 data at AstDyS-2. 2011 SL25 at the JPL Small-Body Database Discovery · Orbit diagram · Orbital elements · Physical parameters

21. Earth-crosser asteroid – An Earth-crosser is a near-Earth asteroid whose orbit crosses that of Earth as observed from the ecliptic pole of Earths orbit. The known numbered Earth-crossers are listed here and those Earth-crossers whose semi-major axes are smaller than Earths are Aten asteroids, the remaining ones are Apollo asteroids. An asteroid with an Earth-crossing orbit is not necessarily in danger of colliding with Earth, the orbit of an Earth-crossing asteroid may not even intersect with that of Earth. This apparent contradiction arises because many asteroids have highly inclined orbits, so although they may have a less than that of Earth. An asteroid for which there is possibility of a collision with Earth at a future date. Specifically, an asteroid is a PHA if its Earth minimum orbital intersection distance is <0.05 AU, the concept of PHA is intended to replace the now abandoned strict definition of ECA which existed for a few years. Having a small MOID is not a guarantee of a collision, on the other hand, small gravitational perturbations of the asteroid around its orbit from planets that it passes can significantly alter its path. For instance,99942 Apophis will approach Earth so closely in 2029 that it will get under the orbit of the Earths geostationary satellites, the Earth will change the trajectory of Apophis and the result may be an even closer approach in the future, possibly 2036. Of the Earth-crossing asteroids,3753 Cruithne is notable for having an orbit that has the period as Earths.2 AU

22. 1620 Geographos – The asteroid 1620 Geographos /dʒiːoʊˈɡræfɒs/ was discovered on September 14,1951, at the Palomar Observatory by Albert George Wilson and Rudolph Minkowski. It was originally given the provisional designation 1951 RA and its name, a Greek word meaning geographer, was chosen to honour geographers and the National Geographic Society. Geographos is a Mars-crosser asteroid and a near-Earth object belonging to the Apollos, the resultant images show Geographos to be the most elongated object in the solar system, it measures 5. 1×1.8 km. Geographos is an S-type asteroid, meaning that it is reflective and composed of nickel-iron mixed with iron-. Geographos was to be explored by the U. S. s Clementine mission, however,1620 Geographos is a potentially hazardous asteroid because its minimum orbit intersection distance is less than 0.05 AU and its diameter is greater than 150 meters. Its orbit is well-determined for the several hundred years

23. 1865 Cerberus – 1865 Cerberus, provisional designation 1971 UA, is a stony asteroid and near-Earth object of the Apollo group, approximately 1.6 kilometers in diameter. It was discovered on 26 October 1971, by Czech astronomer Luboš Kohoutek at the Hamburger Bergedorf Observatory in Germany, the S-type asteroid orbits the Sun at a distance of 0. 6–1.6 AU once every 1 years and 1 month. Its orbit has an eccentricity of 0.47 and an inclination of 16° with respect to the ecliptic and it also makes close approaches to Mars and Venus. The minor planet is named after the figure from Greek mythology, Cerberus, a dog that guarded the entrance to Hades. His capture marked the last of the labors of Hercules. It is also the name of a constellation, Cerberus. Naming citation was published before November 1977

24. 3361 Orpheus – 3361 Orpheus is an Apollo asteroid that was discovered on April 24,1982 by Carlos Torres at Cerro El Roble Astronomical Station. Its eccentric orbit crosses that of Mars and Earth, and approaches Venus as well, from 1900 to 2100 it passes closer than 30 Gm to Venus 11, Earth 33, and Mars 14 times. It passed by Earth at a distance of about 40 lunar distances on December 7,2013,3361 Orpheus is a potentially hazardous asteroid because its minimum orbit intersection distance is less than 0.05 AU and its diameter is greater than 150 meters. Its orbit is well-determined for the several hundred years. The orbital solution includes non-gravitational forces,3361 Orpheus had been one of the originally proposed targets for the Near Earth Asteroid Rendezvous mission. The proposed AIDA may make an observation of 3361 Orpheus during its trajectory to asteroid 65803 Didymos. 3361 Orpheus at the JPL Small-Body Database Discovery · Orbit diagram · Orbital elements · Physical parameters

25. 3362 Khufu – 3362 Khufu is a near-Earth asteroid. It was discovered by R. Scott Dunbar and Maria A. Barucci at the Palomar Observatory in San Diego County, California and its provisional designation was 1984 QA. It is named after Khufu, an ancient Egyptian pharaoh, Khufu was the 4th Aten asteroid to be numbered. 3362 Khufu is a potentially hazardous asteroid because its minimum orbit intersection distance is less than 0.05 AU and its orbit is well-determined for the next several hundred years. Khufu crosses the orbits of Mars, Earth, and Venus, from 1900 to 2100 it drew nearer than 30 Gm to Mercury 26, Venus 27, Earth 20, and Mars 11 times. Venus-crosser asteroid Mars-crosser asteroid 3362 Khufu at the JPL Small-Body Database Discovery · Orbit diagram · Orbital elements · Physical parameters calculations by SOLEX

26. 3753 Cruithne – 3753 Cruithne is a Q-type, Aten asteroid in orbit around the Sun in 1,1 orbital resonance with Earth, making it a co-orbital object. It is an asteroid that, relative to Earth, orbits the Sun in an orbit that effectively describes a horseshoe. It has been incorrectly called Earths second moon, Cruithne does not orbit Earth and at times it is on the other side of the Sun, placing Cruithne well outside of Earths Hill sphere. Its orbit takes it inside the orbit of Mercury and outside the orbit of Mars, Cruithne orbits the Sun in about 1 year but it takes 770 years for the series to complete a horseshoe-shaped movement around the Earth. The name Cruithne is from Old Irish and refers to the early Picts in the Annals of Ulster, Cruithne was discovered on October 10,1986, by Duncan Waldron on a photographic plate taken with the UK Schmidt Telescope at Siding Spring Observatory, Coonabarabran, Australia. The 1983 apparition is credited to Giovanni de Sanctis and Richard M. West of the European Southern Observatory in Chile. It was not until 1997 that its orbit was determined by Paul Wiegert and Kimmo Innanen, working at York University in Toronto. Cruithne is approximately 5 kilometres in diameter, and its closest approach to Earth is 12 million kilometres, from 1994 through 2015, Cruithne made its annual closest approach to Earth every November. Although Cruithnes orbit is not thought to be stable over the term, calculations by Wiegert. There is no danger of a collision with Earth for millions of years and its orbital path and Earths do not cross, and its orbital plane is currently tilted to that of the Earth by 19. 8°. Cruithne, having a maximum magnitude of +15.8, is fainter than Pluto. Cruithne is in an elliptic orbit around the Sun. Its period of revolution around the Sun, approximately 364 days at present, is almost equal to that of the Earth, because of this, Cruithne and Earth appear to follow each other in their paths around the Sun. This is why Cruithne is sometimes called Earths second moon, however, it does not orbit the Earth and is not a moon. In 2058, Cruithne will come within 0.09 AU of Mars, the kidney bean will then start to migrate away from the Earth again in the opposite direction – instead of the Earth falling behind the bean, the Earth is pulling away from the bean. The next such series of close approaches will be centred on the year 2292 – in July of that year, more near-resonant near-Earth objects have since been discovered. These include 54509 YORP,1998 UP1,2002 AA29, and 2009 BD which exist in resonant orbits similar to Cruithnes,2010 TK7 is the first and so far only identified Earth trojan. Other examples of natural bodies known to be in horseshoe orbits include Janus and Epimetheus, the orbits these two moons follow around Saturn are much simpler than the one Cruithne follows, but operate along the same general principles

27. Jet Propulsion Laboratory – The Jet Propulsion Laboratory is a federally funded research and development center and NASA field center in La Cañada Flintridge, California and Pasadena, California, United States. The JPL is managed by the nearby California Institute of Technology for NASA, the laboratorys primary function is the construction and operation of planetary robotic spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASAs Deep Space Network and they are also responsible for managing the JPL Small-Body Database, and provides physical data and lists of publications for all known small Solar System bodies. The JPLs Space Flight Operations Facility and Twenty-Five-Foot Space Simulator are designated National Historic Landmarks, JPL traces its beginnings to 1936 in the Guggenheim Aeronautical Laboratory at the California Institute of Technology when the first set of rocket experiments were carried out in the Arroyo Seco. Malinas thesis advisor was engineer/aerodynamicist Theodore von Kármán, who arranged for U. S. Army financial support for this GALCIT Rocket Project in 1939. In 1941, Malina, Parsons, Forman, Martin Summerfield, in 1943, von Kármán, Malina, Parsons, and Forman established the Aerojet Corporation to manufacture JATO motors. The project took on the name Jet Propulsion Laboratory in November 1943, during JPLs Army years, the laboratory developed two deployed weapon systems, the MGM-5 Corporal and MGM-29 Sergeant intermediate range ballistic missiles. These missiles were the first US ballistic missiles developed at JPL and it also developed a number of other weapons system prototypes, such as the Loki anti-aircraft missile system, and the forerunner of the Aerobee sounding rocket. At various times, it carried out testing at the White Sands Proving Ground, Edwards Air Force Base. A lunar lander was developed in 1938-39 which influenced design of the Apollo Lunar Module in the 1960s. The team lost that proposal to Project Vanguard, and instead embarked on a project to demonstrate ablative re-entry technology using a Jupiter-C rocket. They carried out three successful flights in 1956 and 1957. Using a spare Juno I, the two organizations then launched the United States first satellite, Explorer 1, on February 1,1958, JPL was transferred to NASA in December 1958, becoming the agencys primary planetary spacecraft center. JPL engineers designed and operated Ranger and Surveyor missions to the Moon that prepared the way for Apollo, JPL also led the way in interplanetary exploration with the Mariner missions to Venus, Mars, and Mercury. In 1998, JPL opened the Near-Earth Object Program Office for NASA, as of 2013, it has found 95% of asteroids that are a kilometer or more in diameter that cross Earths orbit. JPL was early to employ women mathematicians, in the 1940s and 1950s, using mechanical calculators, women in an all-female computations group performed trajectory calculations. In 1961, JPL hired Dana Ulery as their first woman engineer to work alongside male engineers as part of the Ranger and Mariner mission tracking teams, when founded, JPLs site was a rocky flood-plain just outside the city limits of Pasadena. Almost all of the 177 acres of the U. S, the city of La Cañada Flintridge, California was incorporated in 1976, well after JPL attained international recognition with a Pasadena address

28. 1566 Icarus – 1566 Icarus is an Apollo asteroid that at perihelion comes closer to the Sun than Mercury, i. e. it is a Mercury-crossing asteroid. It is also a Venus and Mars-crosser and it is named after Icarus of Greek mythology, who flew too close to the Sun. It was discovered on 27 June 1949 by Walter Baade at Palomar Observatory, from 1949 until the discovery of 3200 Phaethon in 1983, it was known as the asteroid that passed closest to the Sun. Icarus is the lowest numbered potentially hazardous asteroid, Icarus makes close approaches to Earth in June at intervals of 9,19, or 28 years. Rarely, it comes as close as 0.042482 AU, during this approach, Icarus became the first minor planet to be observed using radar, with measurements obtained at the Haystack Observatory and the Goldstone Tracking Station. As of 2015, the last close approach was on 16 June 2015, before that, the previous close approach was on 11 June 1996, at 0.10119 AU, almost 40 times as far as the Moon. The next notably close approach will be on 13 June 2043,1566 Icarus is being studied to better understand general relativity, solar oblateness, and Yarkovsky drift. Perihelion precession, caused by general relativity, in the case of Icarus is 10.05 arcseconds per Julian century, Project Icarus was conducted in the spring of 1967. Time magazine ran an article on the endeavor in June 1967, the report later served as the basis and inspiration for the 1979 science fiction film Meteor. com about Project Icarus

29. 1862 Apollo – 1862 Apollo /əˈpɒloʊ/ is a stony asteroid, approximately 1.5 kilometers in diameter, classified as a near-Earth object. It was discovered by German astronomer Karl Reinmuth at Heidelberg Observatory on 24 April 1932, in addition, since Apollos orbit is highly eccentric, it crosses the orbits of Venus and Mars and is therefore called a Venus-crosser and Mars-crosser as well. The analysis of its rotation provided observational evidence of the YORP effect and it is named after the Greek god Apollo. He is the god of the Sun, child of Zeus and Leto, after which the minor planets 5731 Zeus and 68 Leto are named. On November 4,2005, it was announced that a moon, or satellite of Apollo, had been detected by radar observations from Arecibo Observatory, Puerto Rico. The standard provisional designation for this satellite is S/20051, the announcement is contained in the International Astronomical Union Circular 8627. The satellite is only 80 m across and orbits Apollo just 3 km away from the asteroid itself, from the surface of Apollo, S/20051 would have an angular diameter of about 2.0835 degrees. 1862 Apollo is a potentially hazardous asteroid because its minimum orbit intersection distance is less than 0.05 AU, Apollos Earth MOID is 0.0257 AU. Its orbit is well-determined for the several hundred years. On 17 May 2075 it will pass 0.0083 AU from Venus, lost asteroid Lightcurve plot of 1862 Apollo, Palmer Divide Observatory, B. D. Warner Asteroids with Satellites, Robert Johnston, johnstonsarchive

Mars [videos]
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System after Mercury. In English,
Exposure of silica-rich dust uncovered by the Spirit rover
Photomicrograph by Opportunity showing a gray hematite concretion, nicknamed "blueberries", indicative of the past existence of liquid water
North polar early summer ice cap (1999)
South polar midsummer ice cap (2000)
Asteroid [videos]
Asteroids are minor planets, especially those of the inner Solar System. The larger ones have also been called
Image: (253) mathilde
243 Ida and its moon Dactyl. Dactyl is the first satellite of an asteroid to be discovered.
First asteroid image (Ceres and Vesta) from Mars – viewed by ''Curiosity'' (20 April 2014).
A composite image, to scale, of the asteroids that have been imaged at high resolution except Ceres. As of 2011 they are, from largest to smallest: 4 Vesta, 21 Lutetia, 253 Mathilde, 243 Ida and its moon Dactyl, 433 Eros, 951 Gaspra, 2867 Šteins, 25143 Itokawa.
Near-Earth object [videos]
A near-Earth object (NEO) is any small Solar System body whose orbit can bring it into proximity with Earth. By
Image: Asteroid 2006DP14
Very Large Telescope image of the very faint near-Earth asteroid 2009 FD
Asteroid Toutatis from Paranal
Asteroid 4179 Toutatis is a potentially hazardous object that has passed within 2.3 lunar distances
Asteroid belt [videos]
The asteroid belt is the circumstellar disc in the Solar System located roughly between the orbits of the planets Mars
By far the largest object within the belt is Ceres. The total mass of the asteroid belt is significantly less than Pluto's, and approximately twice that of Pluto's moon Charon.
Johannes Kepler, who first noticed in 1596 that there was something strange about the orbits of Mars and Jupiter.
Giuseppe Piazzi, discoverer of Ceres, the largest object in the asteroid belt. For several decades after its discovery Ceres was known as a planet, after which it was reclassified as asteroid. In 2006, it was designated as a dwarf planet.
951 Gaspra, the first asteroid imaged by a spacecraft, as viewed during Galileos 1991 flyby; colors are exaggerated
Jet Propulsion Laboratory [videos]
The Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center in La
The control room at JPL
MSL mockup compared with the Mars Exploration Rover and Sojourner rover by the Jet Propulsion Laboratory on May 12, 2008
Research rockets on display at JPL.
A 1960s advert, it reads: "When you were a kid, science fiction gave you a sense of wonder. Now you feel the same just by going to work."
Orbit [videos]
In physics, an orbit is the gravitationally curved trajectory of an object, such as the trajectory of a planet around a
Conic sections describe the possible orbits (yellow) of small objects around the Earth. A projection of these orbits onto the gravitational potential (blue) of the Earth makes it possible to determine the orbital energy at each point in space.
Image: Orbitalaltitudes
This image shows the four trajectory categories with the gravitational potential well of the central mass's field of potential energy shown in black and the height of the kinetic energy of the moving body shown in red extending above that, correlating to changes in speed as distance changes according to Kepler's laws.
3753 Cruithne [videos]
3753 Cruithne (kroo-EE-nyə or KRUUN-yə) is a Q-type, Aten asteroid in orbit around the Sun in 1:1 orbital resonance
Image: Cruithne
Cruithne's distance to Earth (blue) and the Sun (yellow) plotted over 500 years (top) and 10 years (bottom).
Figure 1. Plan showing possible orbits along gravitational contours (not to scale)
Lagrangian point [videos]
In celestial mechanics, the Lagrangian points (also Lagrange points, L-points, or libration points) are positions in
Net radial acceleration of a point orbiting along the Earth-Moon line.
Image: Lagrangian points equipotential
The satellite ACE in an orbit around L1
Lagrange points in the Sun–Earth system (not to scale)
4179 Toutatis [videos]
4179 Toutatis (too-TAH-tis), provisional designation 1989 AC, is an elongated, stony asteroid and slow rotator,
Toutatis imaged by Chang'e 2 during its flyby
Image: Asteroid 4179 Toutatis.faces model
3200 Phaethon [videos]
3200 Phaethon (FAY-ə-thon, sometimes incorrectly spelled Phaeton), provisional designation 1983 TB, is an Apollo
Image: Asteroid Phaethon 25dec 2010 stack
The elliptical orbit of 3200 Phaethon crosses the orbits of Mars, Earth, Venus and Mercury
Image: 3200 Phaethon skypath Dec 2017
Astronomical unit [videos]
The astronomical unit (symbol: au or ua) is a unit of length, roughly the distance from Earth to the Sun. However, that
The red line indicates the Earth–Sun distance, which on average is about 1 astronomical unit.
Transits of Venus across the face of the Sun were, for a long time, the best method of measuring the astronomical unit, despite the difficulties (here, the so-called "black drop effect") and the rarity of observations.
The astronomical unit is used as the baseline of the triangle to measure stellar parallaxes (distances in the image are not to scale).
Albedo [videos]
Albedo (Latin albedo, "whiteness") is the measure of diffusive reflection of solar radiation out of the total solar
Reflectivity of smooth water at 20 °C (refractive index=1.333)
2003–2004 mean annual clear-sky and total-sky albedo
Percentage of diffusely reflected sunlight in relation to various surface conditions
Amor asteroid [videos]
The Amor asteroids are a group of near-Earth asteroids named after the asteroid 1221 Amor. They approach the orbit of
Amor asteroid Eros visited by NEAR Shoemaker in 2000
Image: Minor Planets Amor
4015 Wilson–Harrington [videos]
4015 Wilson–Harrington is a small Solar System body known both as Comet Wilson–Harrington or 107P/Wilson–Harrington,
4015 Wilson–Harrington at November 19, 1949, from the 48-inch Schmidt telescope at Palomar. The image was enhanced by ESO to show the tail.
4183 Cuno [videos]
4183 Cuno, provisional designation 1959 LM, is an eccentric, rare-type asteroid, classified as near-Earth object and
Image: 4183 cuno
4660 Nereus [videos]
4660 Nereus (NEER-ee-əs; Greek: Νηρέας, provisional designation 1982 DB) is a small (about 0.33 kilometres (0.21 mi))
Asteroid 4660 Nereus (NASA/JPL 2002)
Hungaria group [videos]
The Hungaria group is a dynamical group of asteroids in the asteroid belt. The Hungaria asteroids orbit the Sun with a
Asteroid groups out to the orbit of Jupiter, showing eccentricity versus semi-major axis. Hungaria asteroids are the leftmost dense grouping in blue. The core region of the asteroid belt is shown in red.
Same as above, however showing inclination versus semi-major axis. Again Hungaria asteroids are the (top-)leftmost dense grouping in blue.
Eccentricity versus semi-major axis: Former location of the hypothetical E-belt asteroids (green outline), with current main belt asteroids (red dots) and Hungaria asteroids (green dots).
3362 Khufu [videos]
3362 Khufu is a near-Earth asteroid. It was discovered by R. Scott Dunbar and Maria A. Barucci at the Palomar
Orbit diagram of Khufu asteroid with object location as of May 19, 2013
Image: 3362 Khufu orbit (10 29 07)
Co-orbital configuration [videos]
In astronomy, a co-orbital configuration is a configuration of two or more astronomical objects (such as asteroids,
Rotating-frame depiction of the horseshoe exchange orbits of Janus and Epimetheus
Image: Lagrange very massive