S-type asteroids are asteroids with a spectral type, indicative of a siliceous mineralogical composition, hence the name. 17% of asteroids are of this type, making it the second most common after the carbonaceous C-type. S-types asteroids, with an astronomical albedo of 0.20, are moderately bright and consist of iron- and magnesium-silicates. They are dominant in the inner part of the asteroid belt within 2.2 AU, common in the central belt within about 3 AU, but become rare farther out. The largest is 15 Eunomia, with the next largest members by diameter being 3 Juno, 29 Amphitrite, 532 Herculina and 7 Iris; these largest S-types are visible in 10x50 binoculars at most oppositions. Their spectrum has a moderately steep slope at wavelengths shorter than 0.7 micrometres, has moderate to weak absorption features around 1 µm and 2 µm. The 1 µm absorption is indicative of the presence of silicates. There is a broad but shallow absorption feature centered near 0.63 µm. The composition of these asteroids is similar to a variety of stony meteorites which share similar spectral characteristics.
In the SMASS classification, several "stony" types of asteroids are brought together into a wider S-group which contains the following types: A-type K-type L-type Q-type R-type a "core" S-type for asteroids having the most typical spectra for the S-group Sa, Sk, Sl, Sq, Sr-types containing transition objects between the core S-type and the A, K, L, Q, R-types, respectively. The entire "S"-assemblage of asteroids is spectrally quite distinct from the carbonaceous C-group and the metallic X-group. In the Tholen classification, the S-type is a broad grouping which includes all the types in the SMASS S-group except for the A, Q, R, which have strong "stony" absorption features around 1 μm. Prominent stony asteroid families with their typical albedo are the: Eos family Eunomia family Flora family Koronis family Nysa family Phocaea family Asteroid spectral types X-type asteroid Bus, S. J.. "Phase II of the Small Main-belt Asteroid Spectroscopy Survey: A feature-based taxonomy". Icarus. 158: 146–177.
ArXiv is a repository of electronic preprints approved for posting after moderation, but not full peer review. It consists of scientific papers in the fields of mathematics, astronomy, electrical engineering, computer science, quantitative biology, mathematical finance and economics, which can be accessed online. In many fields of mathematics and physics all scientific papers are self-archived on the arXiv repository. Begun on August 14, 1991, arXiv.org passed the half-million-article milestone on October 3, 2008, had hit a million by the end of 2014. By October 2016 the submission rate had grown to more than 10,000 per month. ArXiv was made possible by the compact TeX file format, which allowed scientific papers to be transmitted over the Internet and rendered client-side. Around 1990, Joanne Cohn began emailing physics preprints to colleagues as TeX files, but the number of papers being sent soon filled mailboxes to capacity. Paul Ginsparg recognized the need for central storage, in August 1991 he created a central repository mailbox stored at the Los Alamos National Laboratory which could be accessed from any computer.
Additional modes of access were soon added: FTP in 1991, Gopher in 1992, the World Wide Web in 1993. The term e-print was adopted to describe the articles, it began as a physics archive, called the LANL preprint archive, but soon expanded to include astronomy, computer science, quantitative biology and, most statistics. Its original domain name was xxx.lanl.gov. Due to LANL's lack of interest in the expanding technology, in 2001 Ginsparg changed institutions to Cornell University and changed the name of the repository to arXiv.org. It is now hosted principally with eight mirrors around the world, its existence was one of the precipitating factors that led to the current movement in scientific publishing known as open access. Mathematicians and scientists upload their papers to arXiv.org for worldwide access and sometimes for reviews before they are published in peer-reviewed journals. Ginsparg was awarded a MacArthur Fellowship in 2002 for his establishment of arXiv; the annual budget for arXiv is $826,000 for 2013 to 2017, funded jointly by Cornell University Library, the Simons Foundation and annual fee income from member institutions.
This model arose in 2010, when Cornell sought to broaden the financial funding of the project by asking institutions to make annual voluntary contributions based on the amount of download usage by each institution. Each member institution pledges a five-year funding commitment to support arXiv. Based on institutional usage ranking, the annual fees are set in four tiers from $1,000 to $4,400. Cornell's goal is to raise at least $504,000 per year through membership fees generated by 220 institutions. In September 2011, Cornell University Library took overall administrative and financial responsibility for arXiv's operation and development. Ginsparg was quoted in the Chronicle of Higher Education as saying it "was supposed to be a three-hour tour, not a life sentence". However, Ginsparg remains on the arXiv Scientific Advisory Board and on the arXiv Physics Advisory Committee. Although arXiv is not peer reviewed, a collection of moderators for each area review the submissions; the lists of moderators for many sections of arXiv are publicly available, but moderators for most of the physics sections remain unlisted.
Additionally, an "endorsement" system was introduced in 2004 as part of an effort to ensure content is relevant and of interest to current research in the specified disciplines. Under the system, for categories that use it, an author must be endorsed by an established arXiv author before being allowed to submit papers to those categories. Endorsers are not asked to review the paper for errors, but to check whether the paper is appropriate for the intended subject area. New authors from recognized academic institutions receive automatic endorsement, which in practice means that they do not need to deal with the endorsement system at all. However, the endorsement system has attracted criticism for restricting scientific inquiry. A majority of the e-prints are submitted to journals for publication, but some work, including some influential papers, remain purely as e-prints and are never published in a peer-reviewed journal. A well-known example of the latter is an outline of a proof of Thurston's geometrization conjecture, including the Poincaré conjecture as a particular case, uploaded by Grigori Perelman in November 2002.
Perelman appears content to forgo the traditional peer-reviewed journal process, stating: "If anybody is interested in my way of solving the problem, it's all there – let them go and read about it". Despite this non-traditional method of publication, other mathematicians recognized this work by offering the Fields Medal and Clay Mathematics Millennium Prizes to Perelman, both of which he refused. Papers can be submitted in any of several formats, including LaTeX, PDF printed from a word processor other than TeX or LaTeX; the submission is rejected by the arXiv software if generating the final PDF file fails, if any image file is too large, or if the total size of the submission is too large. ArXiv now allows one to store and modify an incomplete submission, only finalize the submission when ready; the time stamp on the article is set. The standard access route is through one of several mirrors. Sev
An asteroid family is a population of asteroids that share similar proper orbital elements, such as semimajor axis and orbital inclination. The members of the families are thought to be fragments of past asteroid collisions. An asteroid family is a more specific term than asteroid group whose members, while sharing some broad orbital characteristics, may be otherwise unrelated to each other. Large prominent families contain several hundred recognized asteroids. Small, compact families may have only about ten identified members. About 33% to 35% of asteroids in the main belt are family members. There are about 20 to 30 reliably recognized families, with several tens of less certain groupings. Most asteroid families are found in the main asteroid belt, although several family-like groups such as the Pallas family, Hungaria family, the Phocaea family lie at smaller semi-major axis or larger inclination than the main belt. One family has been identified associated with the dwarf planet Haumea; some studies have tried to find evidence of collisional families among the trojan asteroids, but at present the evidence is inconclusive.
The families are thought to form as a result of collisions between asteroids. In many or most cases the parent body was shattered, but there are several families which resulted from a large cratering event which did not disrupt the parent body; such cratering families consist of a single large body and a swarm of asteroids that are much smaller. Some families have complex internal structures which are not satisfactorily explained at the moment, but may be due to several collisions in the same region at different times. Due to the method of origin, all the members have matching compositions for most families. Notable exceptions are those families. Asteroid families are thought to have lifetimes of the order of a billion years, depending on various factors; this is shorter than the Solar System's age, so few if any are relics of the early Solar System. Decay of families occurs both because of slow dissipation of the orbits due to perturbations from Jupiter or other large bodies, because of collisions between asteroids which grind them down to small bodies.
Such small asteroids become subject to perturbations such as the Yarkovsky effect that can push them towards orbital resonances with Jupiter over time. Once there, they are rapidly ejected from the asteroid belt. Tentative age estimates have been obtained for some families, ranging from hundreds of millions of years to less than several million years as for the compact Karin family. Old families are thought to contain few small members, this is the basis of the age determinations, it is supposed that many old families have lost all the smaller and medium-sized members, leaving only a few of the largest intact. A suggested example of such old family remains are 113 Amalthea pair. Further evidence for a large number of past families comes from analysis of chemical ratios in iron meteorites; these show that there must have once been at least 50 to 100 parent bodies large enough to be differentiated, that have since been shattered to expose their cores and produce the actual meteorites. When the orbital elements of main belt asteroids are plotted, a number of distinct concentrations are seen against the rather uniform distribution of non-family background asteroids.
These concentrations are the asteroid families. Interlopers are asteroids classified as family members based on their so-called proper orbital elements but having spectroscopic properties distinct from the bulk of the family, suggesting that they, contrary to the true family members, did not originate from the same parent body that once fragmented upon a collisional impact. Speaking and their membership are identified by analysing the proper orbital elements rather than the current osculating orbital elements, which fluctuate on timescales of tens of thousands of years; the proper elements are related constants of motion that remain constant for times of at least tens of millions of years, longer. The Japanese astronomer Kiyotsugu Hirayama pioneered the estimation of proper elements for asteroids, first identified several of the most prominent families in 1918. In his honor, asteroid families are sometimes called Hirayama families; this applies to the five prominent groupings discovered by him.
Present day computer-assisted searches have identified more than a hundred asteroid families. The most prominent algorithms have been the hierarchical clustering method, which looks for groupings with small nearest-neighbour distances in orbital element space, wavelet analysis, which builds a density-of-asteroids map in orbital element space, looks for density peaks; the boundaries of the families are somewhat vague because at the edges they blend into the background density of asteroids in the main belt. For this reason the number of members among discovered asteroids is only known and membership is uncertain for asteroids near the edges. Additionally, some interlopers from the heterogeneous background asteroid population are expected in the central regions of a family. Since the true family members caused by the collision are expected to have similar compositions, most such interlopers can in principle be recognised by spectral properties which do not matc
Florentina is a typical Main belt asteroid. It was discovered by Johann Palisa on 15 October 1891 in Vienna, he named the asteroid for Florentine. Between 1874 and 1923, Palisa discovered a total of 122 asteroids. A group of astronomers, including Lucy d'Escoffier Crespo da Silva, contributed data toward the discovery of spin-vector alignments in the Koronis family, which includes Florentina; this was based on observations made between 1998 through 2000. The collaborative work resulted in the creation of 61 new individual rotation lightcurves to augment previous published observations. Lightcurve plot of 321 Florentina, Palmer Divide Observatory, B. D. Warner Asteroid Lightcurve Database, query form Dictionary of Minor Planet Names, Google books Asteroids and comets rotation curves, CdR – Observatoire de Genève, Raoul Behrend Discovery Circumstances: Numbered Minor Planets - – Minor Planet Center 321 Florentina at AstDyS-2, Asteroids—Dynamic Site Ephemeris · Observation prediction · Orbital info · Proper elements · Observational info 321 Florentina at the JPL Small-Body Database Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters
Claudia is a typical Main belt asteroid. It was discovered by Auguste Charlois on 11 June 1891 in Nice; the name was suggested to Charlois by the amateur astronomer Arthur Mee of Cardiff, Wales, to commemorate Mee's wife, Claudia.311 Claudia is one of the Koronis family of asteroids. A group of astronomers, including Lucy D’Escoffier Crespo da Silva and Richard P. Binzel, used observations made between 1998 through 2000 to determine the spin-vector alignment of these asteroids; the collaborative work resulted in the creation of 61 new individual rotation lightcurves to augment previous published observations. 311 Claudia at AstDyS-2, Asteroids—Dynamic Site Ephemeris · Observation prediction · Orbital info · Proper elements · Observational info 311 Claudia at the JPL Small-Body Database Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters
Urda is a main-belt asteroid, discovered by German-American astronomer Christian Heinrich Friedrich Peters on August 28, 1876, in Clinton, New York, named after Urd, one of the Norns in Norse mythology. In 1905, Austrian astronomer Johann Palisa showed. Photometric observations of this asteroid at the Palmer Divide Observatory in Colorado Springs, during 2007–8 gave a light curve with a period of 13.06133 ± 0.00002 hours. This S-type asteroid is a member of the Koronis family of asteroids that share similar orbital elements. In 2002, a diameter estimate of 37.93 ± 3.17 km was obtained from the Midcourse Space Experiment observations, with an albedo of 0.2523 ± 0.0448. A stellar occultation by Urda was observed from Japan on July 23, 2001. Lightcurve plot of 167 Urda, Palmer Divide Observatory, B. D. Warner Asteroid Lightcurve Database, query form Dictionary of Minor Planet Names, Google books Asteroids and comets rotation curves, CdR – Observatoire de Genève, Raoul Behrend Discovery Circumstances: Numbered Minor Planets - – Minor Planet Center 167 Urda at the JPL Small-Body Database Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters
Galileo was an American unmanned spacecraft that studied the planet Jupiter and its moons, as well as several other Solar System bodies. Named after the Italian astronomer Galileo Galilei, it consisted of an entry probe, it was delivered into Earth orbit on October 1989 by Space Shuttle Atlantis. Galileo arrived at Jupiter on December 7, 1995, after gravitational assist flybys of Venus and Earth, became the first spacecraft to orbit Jupiter, it launched the first probe into Jupiter. Despite suffering major antenna problems, Galileo achieved the first asteroid flyby, of 951 Gaspra, discovered the first asteroid moon, around 243 Ida. In 1994, Galileo observed Comet Shoemaker–Levy 9's collision with Jupiter. Jupiter's atmospheric composition and ammonia clouds were recorded, the clouds created by outflows from the lower depths of the atmosphere. Io's volcanism and plasma interactions with Jupiter's atmosphere were recorded; the data Galileo collected supported the theory of a liquid ocean under the icy surface of Europa, there were indications of similar liquid-saltwater layers under the surfaces of Ganymede and Callisto.
Ganymede was shown to possess a magnetic field and the spacecraft found new evidence for exospheres around Europa and Callisto. Galileo discovered that Jupiter's faint ring system consists of dust from impacts on the four small inner moons; the extent and structure of Jupiter's magnetosphere was mapped. On September 21, 2003, after 14 years in space and 8 years in the Jovian system, Galileo's mission was terminated by sending it into Jupiter's atmosphere at a speed of over 48 kilometers per second, eliminating the possibility of contaminating local moons with terrestrial bacteria. Jupiter was rated as the number one priority in the Planetary Science Decadal Survey published in the summer of 1968. In the early 1970s the first flybys of Jupiter were achieved by Pioneer 10 and Pioneer 11, before the decade was out it was visited by the more advanced Voyager 1 and Voyager 2 spacecraft. Work on the spacecraft began at Jet Propulsion Laboratory in 1977, while the Voyager 1 and 2 missions were still being prepared for launch.
Early plans called for a launch on Space Shuttle Columbia on what was codenamed STS-23 in January 1982, but delays in the development of the Space Shuttle allowed more time for development of the probe. As the shuttle program got underway, Galileo was scheduled for launch in 1984, but this slipped to 1985 and to 1986; the mission was called the Jupiter Orbiter Probe. Once the spacecraft was complete, its launch was scheduled for STS-61-G on-board Atlantis in 1986; the Inertial Upper Stage booster was going to be used at first, but this changed to the Centaur booster back to IUS after Challenger. The Centaur-G liquid hydrogen-fueled booster stage allowed a direct trajectory to Jupiter; the mission was further delayed by the hiatus in launches that occurred after the Space Shuttle Challenger disaster. New safety protocols introduced as a result of the disaster prohibited the use of the Centaur-G stage on the Shuttle, forcing Galileo to use a lower-powered Inertial Upper Stage solid-fuel booster.
The mission was re-profiled in 1987 to use several gravitational slingshots, referred to as the Venus-Earth-Earth Gravity Assist or VEEGA maneuvers, to provide the additional velocity required to reach its destination. It was launched on October 18, 1989, by Space Shuttle Atlantis on the STS-34 mission. Galileo flew by Venus at 05:58:48 UTC on February 1990, at a range of 16,106 km. Having gained 8,030 km/h in speed, the spacecraft flew by Earth twice, the first time at a range of 960 km at 20:34:34 UTC on December 8, 1990, before approaching the S-type asteroid 951 Gaspra to a distance of 1,604 km at 22:37 UTC on October 29, 1991. Galileo performed a second flyby of Earth at 303.1 km at 15:09:25 UTC on December 8, 1992, adding 13,320 km/h to its cumulative speed. Galileo performed close observations of a second asteroid, 243 Ida, at 16:51:59 UTC on August 28, 1993, at a range of 2,410 km; the spacecraft discovered Ida has a moon, the first discovery of a natural satellite orbiting an asteroid.
In 1994, Galileo was positioned to watch the fragments of Comet Shoemaker–Levy 9 crash into Jupiter, whereas terrestrial telescopes had to wait to see the impact sites as they rotated into view. After releasing its atmospheric probe on July 13, 1995, the Galileo orbiter became the first man-made satellite of Jupiter at 01:16 UTC on December 8, 1995, after it fired its main engine to enter a 198-day parking orbit. Galileo's prime mission was a two-year study of the Jovian system; the spacecraft traveled around Jupiter in each orbit lasting about two months. The differing distances from Jupiter afforded by these orbits allowed Galileo to sample different parts of the planet's extensive magnetosphere; the orbits were designed for close-up flybys of Jupiter's largest moons. Once the prime mission concluded, an extended mission started on December 7, 1997; the closest approach was 180 km on October 15, 2001. The radiation environment near Io was unhealthy for Galileo's systems, so these flybys were saved for the extended mission when loss of the spacecraft would be more acceptable.
Galileo's cameras were deactivated on January 17, 2002, after they had sustained irreparable radiation damage. NASA engineers were able to recover the damaged tape recorder electronics, Galileo continued to return scientific data until it was deorbited in 2003, performing one last scientific experiment: a measurement