141-501: A Mars-crossing asteroid ( MCA , also Mars-crosser , MC ) is an asteroid whose orbit crosses that of Mars . Some Mars-crossers numbered below 100000 are listed here. They include the two numbered Mars trojans 5261 Eureka and (101429) 1998 VF 31 . Many databases, for instance the JPL Small-Body Database (JPL SBDB), only list asteroids with a perihelion greater than 1.3 AU as Mars-crossers. An asteroid with
282-433: A mantle of hydrated silicates and no core. Because Dawn lacked a magnetometer , it is not known if Ceres has a magnetic field ; it is believed not to. Ceres's internal differentiation may be related to its lack of a natural satellite , as satellites of main belt asteroids are mostly believed to form from collisional disruption, creating an undifferentiated, rubble pile structure. The surface composition of Ceres
423-641: A naturally dark and clear night sky around new moon . An occultation of the star BD+8°471 by Ceres was observed on 13 November 1984 in Mexico, Florida and across the Caribbean , allowing better measurements of its size, shape and albedo. On 25 June 1995, Hubble obtained ultraviolet images of Ceres with 50 km (30 mi) resolution. In 2002, the Keck Observatory obtained infrared images with 30 km (20 mi) resolution using adaptive optics . Before
564-424: A rare-earth element discovered in 1803, was named after the dwarf planet Ceres. The old astronomical symbol of Ceres, still used in astrology, is a sickle , [REDACTED] . The sickle was one of the classical symbols of the goddess Ceres and was suggested, apparently independently, by von Zach and Bode in 1802. It is similar in form to the symbol ⟨♀⟩ (a circle with a small cross beneath) of
705-566: A comet, but "since its movement is so slow and rather uniform, it has occurred to me several times that it might be something better than a comet". In April, Piazzi sent his complete observations to Oriani, Bode, and French astronomer Jérôme Lalande . The information was published in the September 1801 issue of the Monatliche Correspondenz . By this time, the apparent position of Ceres had changed (primarily due to Earth's motion around
846-467: A comet, not an asteroid, if it shows a coma (tail) when warmed by solar radiation, although recent observations suggest a continuum between these types of bodies. Of the roughly one million known asteroids, the greatest number are located between the orbits of Mars and Jupiter , approximately 2 to 4 AU from the Sun, in a region known as the main asteroid belt . The total mass of all the asteroids combined
987-472: A crust, a mantle and a core. No meteorites from Ceres have been found on Earth. Vesta, too, has a differentiated interior, though it formed inside the Solar System's frost line , and so is devoid of water; its composition is mainly of basaltic rock with minerals such as olivine. Aside from the large crater at its southern pole, Rheasilvia , Vesta also has an ellipsoidal shape. Vesta is the parent body of
1128-426: A denser mantle of hydrated silicates. A range of densities for the crust and mantle can be calculated from the types of meteorite thought to have impacted Ceres. With CI-class meteorites (density 2.46 g/cm ), the crust would be approximately 70 km (40 mi) thick and have a density of 1.68 g/cm ; with CM-class meteorites (density 2.9 g/cm ), the crust would be approximately 190 km (120 mi) thick and have
1269-754: A density of 1.9 g/cm . Best-fit modelling yields a crust approximately 40 km (25 mi) thick with a density of approximately 1.25 g/cm , and a mantle/core density of approximately 2.4 g/cm . In 2017, Dawn confirmed that Ceres has a transient atmosphere of water vapour. Hints of an atmosphere had appeared in early 2014, when the Herschel Space Observatory detected localised mid-latitude sources of water vapour on Ceres, no more than 60 km (40 mi) in diameter, which each give off approximately 10 molecules (3 kg) of water per second. Two potential source regions, designated Piazzi (123°E, 21°N) and Region A (231°E, 23°N), were visualised in
1410-644: A diameter of one kilometer or larger. A small number of NEAs are extinct comets that have lost their volatile surface materials, although having a faint or intermittent comet-like tail does not necessarily result in a classification as a near-Earth comet, making the boundaries somewhat fuzzy. The rest of the near-Earth asteroids are driven out of the asteroid belt by gravitational interactions with Jupiter . Many asteroids have natural satellites ( minor-planet moons ). As of October 2021 , there were 85 NEAs known to have at least one moon, including three known to have two moons. The asteroid 3122 Florence , one of
1551-407: A few other asteroids discovered over the next few years. 20 Massalia was the first asteroid that was not assigned an iconic symbol, and no iconic symbols were created after the 1855 discovery of 37 Fides . Many asteroids are the shattered remnants of planetesimals , bodies within the young Sun's solar nebula that never grew large enough to become planets . It is thought that planetesimals in
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#17328587471731692-483: A group headed by Franz Xaver von Zach , editor of the German astronomical journal Monatliche Correspondenz (Monthly Correspondence), sent requests to 24 experienced astronomers (whom he dubbed the " celestial police "), asking that they combine their efforts and begin a methodical search for the expected planet. Although they did not discover Ceres, they later found the asteroids 2 Pallas , 3 Juno and 4 Vesta . One of
1833-502: A heavily cratered surface, though with fewer large craters than expected. Models based on the formation of the current asteroid belt had predicted Ceres should have ten to fifteen craters larger than 400 km (250 mi) in diameter. The largest confirmed crater on Ceres, Kerwan Basin , is 284 km (176 mi) across. The most likely reason for this is viscous relaxation of the crust slowly flattening out larger impacts. Ceres's north polar region shows far more cratering than
1974-405: A large amount of sodium carbonate ( Na 2 CO 3 ) and smaller amounts of ammonium chloride ( NH 4 Cl ) or ammonium bicarbonate ( NH 4 HCO 3 ). These materials have been suggested to originate from the crystallisation of brines that reached the surface. In August 2020 NASA confirmed that Ceres was a water-rich body with a deep reservoir of brine that percolated to
2115-413: A large core, the core–mantle boundary should be warm enough for pockets of brine. With a small core, the mantle should remain liquid below 110 km (68 mi). In the latter case a 2% freezing of the liquid reservoir would compress the liquid enough to force some to the surface, producing cryovolcanism. A second two-layer model suggests a partial differentiation of Ceres into a volatile-rich crust and
2256-567: A less dense but stronger crust that is at most thirty per cent ice by volume. Although Ceres likely lacks an internal ocean of liquid water, brines still flow through the outer mantle and reach the surface, allowing cryovolcanoes such as Ahuna Mons to form roughly every fifty million years. This makes Ceres the closest known cryovolcanically active body to the Sun . Additionally, Ceres hosts an extremely tenuous and transient atmosphere of water vapour, vented from localised sources on its surface. In
2397-510: A new planet . Ceres was later classified as an asteroid and then a dwarf planet, the only one not beyond Neptune 's orbit. Ceres' diameter is about one-fourth that of the Moon . Its small size means that even at its brightest it is too dim to be seen by the naked eye , except under extremely dark skies. Its apparent magnitude ranges from 6.7 to 9.3, peaking at opposition (when it is closest to Earth ) once every 15- to 16-month synodic period . As
2538-402: A new method of placing numbers before their names in order of discovery. The numbering system initially began with the fifth asteroid, 5 Astraea , as number 1, but in 1867, Ceres was adopted into the new system under the name 1 Ceres. By the 1860s, astronomers widely accepted that a fundamental difference existed between the major planets and asteroids such as Ceres, though
2679-465: A numerical procession known as the Titius–Bode law (now discredited). Except for an unexplained gap between Mars and Jupiter, Bode's formula seemed to predict the orbits of the known planets. He wrote the following explanation for the existence of a "missing planet": This latter point seems in particular to follow from the astonishing relation which the known six planets observe in their distances from
2820-599: A perihelion less than this is classed as a near-Earth object even though it is crossing the orbit of Mars as well as crossing (or coming near to) that of Earth. Nevertheless, these objects are listed on this page. A grazer is an object with a perihelion below the aphelion of Mars (1.67 AU) but above the Martian perihelion (1.38 AU). The JPL SBDB lists 13,500 Mars-crossing asteroids. Only 18 MCAs are brighter than absolute magnitude (H) 12.5, which typically makes these asteroids with H<12.5 more than 13 km in diameter depending on
2961-442: A planet". Had this resolution been adopted, it would have made Ceres the fifth planet in order from the Sun, but on 24 August 2006 the assembly adopted the additional requirement that a planet must have " cleared the neighbourhood around its orbit". Ceres is not a planet because it does not dominate its orbit, sharing it as it does with the thousands of other asteroids in the asteroid belt and constituting only about forty per cent of
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#17328587471733102-487: A planet. A proposal before the International Astronomical Union (IAU), the global body responsible for astronomical nomenclature and classification, defined a planet as "a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid-body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of
3243-564: A relatively reflective surface , is normally visible to the naked eye in dark skies when it is favorably positioned. Rarely, small asteroids passing close to Earth may be briefly visible to the naked eye. As of April 2022 , the Minor Planet Center had data on 1,199,224 minor planets in the inner and outer Solar System, of which about 614,690 had enough information to be given numbered designations. In 1772, German astronomer Johann Elert Bode , citing Johann Daniel Titius , published
3384-433: A result, its surface features are barely visible even with the most powerful telescopes, and little was known about it until the robotic NASA spacecraft Dawn approached Ceres for its orbital mission in 2015. Dawn found Ceres's surface to be a mixture of water ice and hydrated minerals such as carbonates and clay . Gravity data suggest Ceres to be partially differentiated into a muddy (ice-rock) mantle/core and
3525-775: A rocky core and icy mantle, or even a liquid water ocean, soon after its formation. This ocean should have left an icy layer under the surface as it froze. The fact that Dawn found no evidence of such a layer suggests that Ceres's original crust was at least partially destroyed by later impacts thoroughly mixing the ice with the salts and silicate-rich material of the ancient seafloor and the material beneath. Ceres possesses surprisingly few large craters, suggesting that viscous relaxation and cryovolcanism have erased older geological features. The presence of clays and carbonates requires chemical reactions at temperatures above 50 °C, consistent with hydrothermal activity. It has become considerably less geologically active over time, with
3666-401: A sample in 2020 which was delivered back to Earth in 2023. NASA's Lucy , launched in 2021, is tasked with studying ten different asteroids, two from the main belt and eight Jupiter trojans . Psyche , launched October 2023, aims to study the metallic asteroid Psyche . Near-Earth asteroids have the potential for catastrophic consequences if they strike Earth, with a notable example being
3807-532: A series of days. Second, the two films or plates of the same region were viewed under a stereoscope . A body in orbit around the Sun would move slightly between the pair of films. Under the stereoscope, the image of the body would seem to float slightly above the background of stars. Third, once a moving body was identified, its location would be measured precisely using a digitizing microscope. The location would be measured relative to known star locations. These first three steps do not constitute asteroid discovery:
3948-467: A single orbit. If so, the object receives a catalogue number and the observer of the first apparition with a calculated orbit is declared the discoverer, and granted the honor of naming the object subject to the approval of the International Astronomical Union . By 1851, the Royal Astronomical Society decided that asteroids were being discovered at such a rapid rate that a different system
4089-408: A stronger resemblance to pit crater chains , which are indicative of buried normal faults . Also, several craters on Ceres have shallow, fractured floors consistent with cryomagmatic intrusion. Ceres has one prominent mountain, Ahuna Mons ; this appears to be a cryovolcano and has few craters, suggesting a maximum age of 240 million years. Its relatively high gravitational field suggests it
4230-456: A surface dominated by impact craters ; nevertheless, evidence from Dawn reveals that internal processes have continued to sculpt Ceres's surface to a significant extent contrary to predictions that Ceres's small size would have ceased internal geological activity early in its history. Although Ceres is not as actively discussed as a potential home for microbial extraterrestrial life as Mars , Europa , Enceladus , or Titan are, it has
4371-417: A traditional symbol for a star, as the generic symbol for an asteroid. The circle was then numbered in order of discovery to indicate a specific asteroid. The numbered-circle convention was quickly adopted by astronomers, and the next asteroid to be discovered ( 16 Psyche , in 1852) was the first to be designated in that way at the time of its discovery. However, Psyche was given an iconic symbol as well, as were
List of Mars-crossing minor planets - Misplaced Pages Continue
4512-416: A water exosphere half-life of 7 hours from the ballistic trajectory model, an outgassing rate of 6 kg/s with an optically thin atmosphere sustained for tens of days using a DSMC model, and seasonal polar caps formed from exosphere water delivery using the polar cap model. The mobility of water molecules within the exosphere is dominated by ballistic hops coupled with interaction of the surface, however less
4653-480: Is 9 hours and 4 minutes; the small equatorial crater of Kait is selected as its prime meridian . Ceres has an axial tilt of 4°, small enough for its polar regions to contain permanently shadowed craters that are expected to act as cold traps and accumulate water ice over time, similar to what occurs on the Moon and Mercury . About 0.14% of water molecules released from the surface are expected to end up in
4794-440: Is a mixture of ice, salts, and hydrated minerals. Under that is a layer that may contain a small amount of brine. This extends to a depth of at least the 100 km (60 mi) limit of detection. Under that is thought to be a mantle dominated by hydrated rocks such as clays. In one two-layer model, Ceres consists of a core of chondrules and a mantle of mixed ice and micron-sized solid particulates ("mud"). Sublimation of ice at
4935-410: Is also known. Numerical orbital dynamics stability simulations indicate that Saturn and Uranus probably do not have any primordial trojans. Near-Earth asteroids, or NEAs, are asteroids that have orbits that pass close to that of Earth. Asteroids that actually cross Earth's orbital path are known as Earth-crossers . As of April 2022 , a total of 28,772 near-Earth asteroids were known; 878 have
5076-503: Is also the largest single geographical feature on Ceres. Two of the three have higher than average ammonium concentrations. Dawn observed 4,423 boulders larger than 105 m (344 ft) in diameter on the surface of Ceres. These boulders likely formed through impacts, and are found within or near craters, though not all craters contain boulders. Large boulders are more numerous at higher latitudes. Boulders on Ceres are brittle and degrade rapidly due to thermal stress (at dawn and dusk,
5217-427: Is by far the largest asteroid, with a diameter of 940 km (580 mi). The next largest are 4 Vesta and 2 Pallas , both with diameters of just over 500 km (300 mi). Vesta is the brightest of the four main-belt asteroids that can, on occasion, be visible to the naked eye. On some rare occasions, a near-Earth asteroid may briefly become visible without technical aid; see 99942 Apophis . The mass of all
5358-520: Is dense, and thus composed more of rock than ice, and that its placement is likely due to diapirism of a slurry of brine and silicate particles from the top of the mantle. It is roughly antipodal to Kerwan Basin. Seismic energy from the Kerwan-forming impact may have focused on the opposite side of Ceres, fracturing the outer layers of the crust and triggering the movement of high-viscosity cryomagma (muddy water ice softened by its content of salts) onto
5499-508: Is evidently the result of space weathering on Ceres's older surfaces; the latter two are volatile under Cererian conditions and would be expected to either escape quickly or settle in cold traps, and so are evidently associated with areas with relatively recent geological activity. Organic compounds were detected in Ernutet Crater, and most of the planet's near surface is rich in carbon, at approximately 20% by mass. The carbon content
5640-414: Is farther from the Sun in its orbit, and internally powered emissions should not be affected by its orbital position. The limited data previously available suggested cometary-style sublimation, but evidence from Dawn suggests geologic activity could be at least partially responsible. Studies using Dawn's gamma ray and neutron detector (GRaND) reveal that Ceres accelerates electrons from the solar wind;
5781-463: Is homogeneous on a global scale, and it is rich in carbonates and ammoniated phyllosilicates that have been altered by water, though water ice in the regolith varies from approximately 10% in polar latitudes to much drier, even ice-free, in the equatorial regions. Studies using the Hubble Space Telescope show graphite , sulfur , and sulfur dioxide on Ceres's surface. The graphite
List of Mars-crossing minor planets - Misplaced Pages Continue
5922-440: Is known about direct interactions with planetary regoliths. Ceres is a surviving protoplanet that formed 4.56 billion years ago; alongside Pallas and Vesta, one of only three remaining in the inner Solar System, with the rest either merging to form terrestrial planets , being shattered in collisions or being ejected by Jupiter. Despite Ceres's current location, its composition is not consistent with having formed within
6063-399: Is moderately tilted relative to that of Earth; its inclination ( i ) is 10.6°, compared to 7° for Mercury and 17° for Pluto. It is also slightly elongated, with an eccentricity ( e ) = 0.08, compared to 0.09 for Mars. Ceres is not part of an asteroid family , probably due to its large proportion of ice, as smaller bodies with the same composition would have sublimated to nothing over
6204-475: Is more than five times higher than in carbonaceous chondrite meteorites analysed on Earth. The surface carbon shows evidence of being mixed with products of rock-water interactions, such as clays. This chemistry suggests Ceres formed in a cold environment, perhaps outside the orbit of Jupiter, and that it accreted from ultra-carbon-rich materials in the presence of water, which could provide conditions favourable to organic chemistry. Dawn revealed that Ceres has
6345-844: Is only 3% that of Earth's Moon . The majority of main belt asteroids follow slightly elliptical, stable orbits, revolving in the same direction as the Earth and taking from three to six years to complete a full circuit of the Sun. Asteroids have historically been observed from Earth. The first close-up observation of an asteroid was made by the Galileo spacecraft . Several dedicated missions to asteroids were subsequently launched by NASA and JAXA , with plans for other missions in progress. NASA's NEAR Shoemaker studied Eros , and Dawn observed Vesta and Ceres . JAXA's missions Hayabusa and Hayabusa2 studied and returned samples of Itokawa and Ryugu , respectively. OSIRIS-REx studied Bennu , collecting
6486-477: Is so slow and rather uniform, it has occurred to me several times that it might be something better than a comet". In April, Piazzi sent his complete observations to Oriani, Bode, and French astronomer Jérôme Lalande . The information was published in the September 1801 issue of the Monatliche Correspondenz . By this time, the apparent position of Ceres had changed (mostly due to Earth's motion around
6627-480: Is that both moons may be captured main-belt asteroids . Both moons have very circular orbits which lie almost exactly in Mars's equatorial plane , and hence a capture origin requires a mechanism for circularizing the initially highly eccentric orbit, and adjusting its inclination into the equatorial plane, most probably by a combination of atmospheric drag and tidal forces , although it is not clear whether sufficient time
6768-439: Is that comets typically have more eccentric orbits than most asteroids; highly eccentric asteroids are probably dormant or extinct comets. The minor planets beyond Jupiter's orbit are sometimes also called "asteroids", especially in popular presentations. However, it is becoming increasingly common for the term asteroid to be restricted to minor planets of the inner Solar System. Therefore, this article will restrict itself for
6909-513: Is the largest asteroid. The IAU has been equivocal on the subject, though its Minor Planet Center , the organisation charged with cataloguing such objects, notes that dwarf planets may have dual designations, and the joint IAU/ USGS /NASA Gazetteer categorises Ceres as both asteroid and a dwarf planet. Ceres follows an orbit between Mars and Jupiter, near the middle of the asteroid belt, with an orbital period (year) of 4.6 Earth years. Compared to other planets and dwarf planets, Ceres's orbit
7050-476: Is too dim to be visible to the average naked eye , but under ideal viewing conditions, keen eyes may be able to see it. Vesta is the only other asteroid that can regularly reach a similarly bright magnitude, while Pallas and 7 Iris do so only when both in opposition and near perihelion. When in conjunction , Ceres has a magnitude of around +9.3, which corresponds to the faintest objects visible with 10×50 binoculars; thus, it can be seen with such binoculars in
7191-467: Is unstable at distances less than 5 AU from the Sun, so it is expected to sublime if exposed directly to solar radiation. Proton emission from solar flares and CMEs can sputter exposed ice patches on the surface, leading to a positive correlation between detections of water vapour and solar activity. Water ice can migrate from the deep layers of Ceres to the surface, but it escapes in a short time. Surface sublimation would be expected to be lower when Ceres
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#17328587471737332-640: The Chicxulub impact , widely thought to have induced the Cretaceous–Paleogene mass extinction . As an experiment to meet this danger, in September 2022 the Double Asteroid Redirection Test spacecraft successfully altered the orbit of the non-threatening asteroid Dimorphos by crashing into it. In 2006, the International Astronomical Union (IAU) introduced the currently preferred broad term small Solar System body , defined as an object in
7473-509: The Dawn mission, only a few surface features had been unambiguously detected on Ceres. High-resolution ultraviolet Hubble images in 1995 showed a dark spot on its surface, which was nicknamed "Piazzi" in honour of the discoverer of Ceres. It was thought to be a crater. Visible-light images of a full rotation taken by Hubble in 2003 and 2004 showed eleven recognisable surface features, the natures of which were undetermined. One of them corresponded to
7614-407: The Dawn spacecraft found a mean diameter of 939.4 km (583.7 mi) and a mass of 9.38 × 10 kg . This gives Ceres a density of 2.16 g/cm , suggesting that a quarter of its mass is water ice. Ceres makes up 40% of the estimated (2394 ± 5) × 10 kg mass of the asteroid belt, and it has 3 + 1 ⁄ 2 times the mass of the next asteroid, Vesta , but it is only 1.3%
7755-509: The Moon . L 4 ( leading cloud ): L 5 ( trailing cloud ): Candidates These objects are not catalogued as Mars-crossers in databases such as the Jet Propulsion Laboratory 's online Small-body Database Browser . Instead, they are categorized as Near Earth Objects (NEOs). Asteroid An asteroid is a minor planet —an object that is neither a true planet nor an identified comet — that orbits within
7896-456: The Solar System that is neither a planet , a dwarf planet , nor a natural satellite ; this includes asteroids, comets, and more recently discovered classes. According to IAU, "the term 'minor planet' may still be used, but generally, 'Small Solar System Body' will be preferred." Historically, the first discovered asteroid, Ceres , was at first considered a new planet. It was followed by
8037-602: The Vestian family and other V-type asteroids , and is the source of the HED meteorites , which constitute 5% of all meteorites on Earth. 1 Ceres Ceres ( minor-planet designation : 1 Ceres ) is a dwarf planet in the middle main asteroid belt between the orbits of Mars and Jupiter . It was the first known asteroid , discovered on 1 January 1801 by Giuseppe Piazzi at Palermo Astronomical Observatory in Sicily , and announced as
8178-424: The albedo . The smallest known MCAs have an absolute magnitude (H) of around 24 and are typically less than 100 meters in diameter. There are over 21,600 known Mars-crossers of which only 5751 have received a MPC number. Earth having more gravity and surface area than Mars attracts more impactors than Mars. Earth is impacted about 20 times more than the Moon, and Mars only gets impacted about 3 to 5 times more than
8319-403: The inner Solar System . They are rocky, metallic, or icy bodies with no atmosphere, classified as C-type ( carbonaceous ), M-type ( metallic ), or S-type ( silicaceous ). The size and shape of asteroids vary significantly, ranging from small rubble piles under a kilometer across and larger than meteoroids , to Ceres , a dwarf planet almost 1000 km in diameter. A body is classified as
8460-484: The near infrared as dark areas (Region A also has a bright centre) by the Keck Observatory . Possible mechanisms for the vapour release are sublimation from approximately 0.6 km (0.2 sq mi) of exposed surface ice, cryovolcanic eruptions resulting from radiogenic internal heat, or pressurisation of a subsurface ocean due to thickening of an overlying layer of ice. In 2015, David Jewitt included Ceres in his list of active asteroids . Surface water ice
8601-467: The protoplanetary disk , and in this region the accretion of planetesimals into planets during the formative period of the Solar System was prevented by large gravitational perturbations by Jupiter . Contrary to popular imagery, the asteroid belt is mostly empty. The asteroids are spread over such a large volume that reaching an asteroid without aiming carefully would be improbable. Nonetheless, hundreds of thousands of asteroids are currently known, and
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#17328587471738742-421: The thermal infrared suggest a composition containing mainly phyllosilicates , which are well known from the surface of Mars. The spectra are distinct from those of all classes of chondrite meteorites, again pointing away from an asteroidal origin. Both sets of findings support an origin of Phobos from material ejected by an impact on Mars that reaccreted in Martian orbit, similar to the prevailing theory for
8883-449: The " celestial police ", asking that they combine their efforts and begin a methodical search for the expected planet. Although they did not discover Ceres, they later found the asteroids Pallas , Juno , and Vesta . One of the astronomers selected for the search was Giuseppe Piazzi , a Catholic priest at the academy of Palermo, Sicily . Before receiving his invitation to join the group, Piazzi discovered Ceres on 1 January 1801. He
9024-402: The "missing planet" he had proposed to exist between Mars and Jupiter. Ceres was assigned a planetary symbol and remained listed as a planet in astronomy books and tables (along with Pallas, Juno, and Vesta) for over half a century. As other objects were discovered in the neighbourhood of Ceres, astronomers began to suspect that it represented the first of a new class of objects. When Pallas
9165-552: The Ancient Greek ἀστήρ astēr 'star, planet'. In the early second half of the 19th century, the terms asteroid and planet (not always qualified as "minor") were still used interchangeably. Traditionally, small bodies orbiting the Sun were classified as comets , asteroids, or meteoroids , with anything smaller than one meter across being called a meteoroid. The term asteroid, never officially defined, can be informally used to mean "an irregularly shaped rocky body orbiting
9306-512: The Earth, that the stronger chafe the weaker, and are Jupiter and Saturn destined to plunder forever?" In 1772, German astronomer Johann Elert Bode , citing Johann Daniel Titius , published a formula later known as the Titius–Bode law that appeared to predict the orbits of the known planets but for an unexplained gap between Mars and Jupiter. This formula predicted that there ought to be another planet with an orbital radius near 2.8 astronomical units (AU), or 420 million km, from
9447-640: The Jovian disruption. Ceres and Vesta grew large enough to melt and differentiate , with heavy metallic elements sinking to the core, leaving rocky minerals in the crust. In the Nice model , many Kuiper-belt objects are captured in the outer asteroid belt, at distances greater than 2.6 AU. Most were later ejected by Jupiter, but those that remained may be the D-type asteroids , and possibly include Ceres. Various dynamical groups of asteroids have been discovered orbiting in
9588-522: The Piazzi feature. Near-infrared images over a whole rotation, taken with adaptive optics by the Keck Observatory in 2012, showed bright and dark features moving with Ceres's rotation. Two dark features were circular and were presumed to be craters; one was observed to have a bright central region, and the other was identified as the Piazzi feature. Dawn eventually revealed Piazzi to be a dark region in
9729-532: The Sun that does not qualify as a planet or a dwarf planet under the IAU definitions". The main difference between an asteroid and a comet is that a comet shows a coma (tail) due to sublimation of its near-surface ices by solar radiation. A few objects were first classified as minor planets but later showed evidence of cometary activity. Conversely, some (perhaps all) comets are eventually depleted of their surface volatile ices and become asteroid-like. A further distinction
9870-446: The Sun) and was too close to the Sun's glare for other astronomers to confirm Piazzi's observations. Towards the end of the year, Ceres should have been visible again, but after such a long time, it was difficult to predict its exact position. To recover Ceres, mathematician Carl Friedrich Gauss , then twenty-four years old, developed an efficient method of orbit determination . He predicted
10011-406: The Sun), and was too close to the Sun's glare for other astronomers to confirm Piazzi's observations. Toward the end of the year, Ceres should have been visible again, but after such a long time it was difficult to predict its exact position. To recover Ceres, mathematician Carl Friedrich Gauss , then 24 years old, developed an efficient method of orbit determination . In a few weeks, he predicted
10152-401: The Sun, their volatile ices would sublimate , and traditional approaches would classify them as comets. The Kuiper-belt bodies are called "objects" partly to avoid the need to classify them as asteroids or comets. They are thought to be predominantly comet-like in composition, though some may be more akin to asteroids. Most do not have the highly eccentric orbits associated with comets, and
10293-406: The Sun. The Titius–Bode law gained more credence with William Herschel 's 1781 discovery of Uranus near the predicted distance for a planet beyond Saturn . In 1800, a group headed by Franz Xaver von Zach , editor of the German astronomical journal Monatliche Correspondenz [ de ] ( Monthly Correspondence ), sent requests to twenty-four experienced astronomers, whom he dubbed
10434-484: The Sun. Let the distance from the Sun to Saturn be taken as 100, then Mercury is separated by 4 such parts from the Sun. Venus is 4 + 3 = 7. The Earth 4 + 6 = 10. Mars 4 + 12 = 16. Now comes a gap in this so orderly progression. After Mars there follows a space of 4 + 24 = 28 parts, in which no planet has yet been seen. Can one believe that the Founder of the universe had left this space empty? Certainly not. From here we come to
10575-544: The accretion epoch), whereas most smaller asteroids are products of fragmentation of primordial asteroids. The primordial population of the main belt was probably 200 times what it is today. Three largest objects in the asteroid belt, Ceres , Vesta , and Pallas , are intact protoplanets that share many characteristics common to planets, and are atypical compared to the majority of irregularly shaped asteroids. The fourth-largest asteroid, Hygiea , appears nearly spherical although it may have an undifferentiated interior, like
10716-448: The addition of two planets: one between Jupiter and Mars and one between Venus and Mercury. Other theoreticians, such as Immanuel Kant , pondered whether the gap had been created by the gravity of Jupiter; in 1761, astronomer and mathematician Johann Heinrich Lambert asked: "And who knows whether already planets are missing which have departed from the vast space between Mars and Jupiter? Does it then hold of celestial bodies as well as of
10857-433: The age of the Solar System. Ceres is the largest asteroid in the main asteroid belt. It has been classified as a C‑type or carbonaceous asteroid and, due to the presence of clay minerals, as a G-type asteroid . It has a similar, but not identical, composition to that of carbonaceous chondrite meteorites. It is an oblate spheroid, with an equatorial diameter 8% larger than its polar diameter. Measurements from
10998-555: The age of the Solar System. It was once thought to be a member of the Gefion family , the members of which share similar proper orbital elements , suggesting a common origin through an asteroid collision in the past. Ceres was later found to have a different composition from the Gefion family and appears to be an interloper , having similar orbital elements but not a common origin. Due to their small masses and large separations, objects within
11139-502: The asteroid belt evolved much like the rest of objects in the solar nebula until Jupiter neared its current mass, at which point excitation from orbital resonances with Jupiter ejected over 99% of planetesimals in the belt. Simulations and a discontinuity in spin rate and spectral properties suggest that asteroids larger than approximately 120 km (75 mi) in diameter accreted during that early era, whereas smaller bodies are fragments from collisions between asteroids during or after
11280-504: The asteroid belt is estimated to be 2.39 × 10 kg, which is just 3% of the mass of the Moon; the mass of the Kuiper Belt and Scattered Disk is over 100 times as large. The four largest objects, Ceres, Vesta, Pallas, and Hygiea, account for maybe 62% of the belt's total mass, with 39% accounted for by Ceres alone. Trojans are populations that share an orbit with a larger planet or moon, but do not collide with it because they orbit in one of
11421-597: The asteroid belt rarely fall into gravitational resonances with each other. Nevertheless, Ceres is able to capture other asteroids into temporary 1:1 resonances (making them temporary trojans ), for periods from a few hundred thousand to more than two million years. Fifty such objects have been identified. Ceres is close to a 1:1 mean-motion orbital resonance with Pallas (their proper orbital periods differ by 0.2%), but not close enough to be significant over astronomical timescales. The rotation period of Ceres (the Cererian day)
11562-706: The asteroid belt. It seems rather that it formed between the orbits of Jupiter and Saturn, and was deflected into the asteroid belt as Jupiter migrated outward. The discovery of ammonium salts in Occator Crater supports an origin in the outer Solar System, as ammonia is far more abundant in that region. The early geological evolution of Ceres was dependent on the heat sources available during and after its formation: impact energy from planetesimal accretion and decay of radionuclides (possibly including short-lived extinct radionuclides such as aluminium-26 ). These may have been sufficient to allow Ceres to differentiate into
11703-494: The asteroid later named 5 Astraea . It was the first new asteroid discovery in 38 years. Carl Friedrich Gauss was given the honor of naming the asteroid. After this, other astronomers joined; 15 asteroids were found by the end of 1851. In 1868, when James Craig Watson discovered the 100th asteroid, the French Academy of Sciences engraved the faces of Karl Theodor Robert Luther , John Russell Hind , and Hermann Goldschmidt ,
11844-595: The astronomers selected for the search was Giuseppe Piazzi , a Catholic priest at the Academy of Palermo, Sicily. Before receiving his invitation to join the group, Piazzi discovered Ceres on 1 January 1801. He was searching for "the 87th [star] of the Catalogue of the Zodiacal stars of Mr la Caille ", but found that "it was preceded by another". Instead of a star, Piazzi had found a moving star-like object, which he first thought
11985-409: The belt's total mass. Bodies that met the first proposed definition but not the second, such as Ceres, were instead classified as dwarf planets . Planetary geologists still often ignore this definition and consider Ceres to be a planet anyway. Ceres is a dwarf planet, but there is some confusion about whether it is also an asteroid. A NASA webpage states that Vesta, the belt's second-largest object,
12126-473: The bright spots. In March 2016 Dawn found definitive evidence of water ice on the surface of Ceres at Oxo crater . On 9 December 2015, NASA scientists reported that the bright spots on Ceres may be due to a type of salt from evaporated brine containing magnesium sulfate hexahydrate (MgSO 4 ·6H 2 O); the spots were also found to be associated with ammonia-rich clays. Near-infrared spectra of these bright areas were reported in 2017 to be consistent with
12267-479: The course of the last three million years has triggered cyclical shifts in Ceres's axial tilt, ranging from two to twenty degrees, meaning that seasonal variation in sun exposure has occurred in the past, with the last period of seasonal activity estimated at 14,000 years ago. Those craters that remain in shadow during periods of maximum axial tilt are the most likely to retain water ice from eruptions or cometary impacts over
12408-399: The crust. Models suggest that, over the past billion years, one cryovolcano has formed on Ceres on average every fifty million years. The eruptions may be linked to ancient impact basins but are not uniformly distributed over Ceres. The model suggests that, contrary to findings at Ahuna Mons, Cererian cryovolcanoes must be composed of far less dense material than average for Ceres's crust, or
12549-631: The densities of the core and mantle/crust to be 2.46–2.90 and 1.68–1.95 g/cm respectively, with the mantle and crust together being 70–190 km (40–120 mi) thick. Only partial dehydration (expulsion of ice) from the core is expected, though the high density of the mantle relative to water ice reflects its enrichment in silicates and salts. That is, the core (if it exists), the mantle and crust all consist of rock and ice, though in different ratios. Ceres's mineral composition can be determined (indirectly) only for its outer 100 km (60 mi). The solid outer crust, 40 km (25 mi) thick,
12690-462: The discovery of other similar bodies, which with the equipment of the time appeared to be points of light like stars, showing little or no planetary disc, though readily distinguishable from stars due to their apparent motions. This prompted the astronomer Sir William Herschel to propose the term asteroid , coined in Greek as ἀστεροειδής, or asteroeidēs , meaning 'star-like, star-shaped', and derived from
12831-406: The distance of Jupiter by 4 + 48 = 52 parts, and finally to that of Saturn by 4 + 96 = 100 parts. Bode's formula predicted another planet would be found with an orbital radius near 2.8 astronomical units (AU), or 420 million km, from the Sun. The Titius–Bode law got a boost with William Herschel 's discovery of Uranus near the predicted distance for a planet beyond Saturn . In 1800,
12972-594: The equatorial region, with the eastern equatorial region in particular comparatively lightly cratered. The overall size frequency of craters of between twenty and a hundred kilometres (10–60 mi) is consistent with their having originated in the Late Heavy Bombardment , with craters outside the ancient polar regions likely erased by early cryovolcanism . Three large shallow basins (planitiae) with degraded rims are likely to be eroded craters. The largest, Vendimia Planitia , at 800 km (500 mi) across,
13113-468: The fourth, when I had the satisfaction to see it had moved at the same rate as on the preceding days. Piazzi observed Ceres a total of 24 times, the final time on 11 February 1801, when illness interrupted his work. He announced his discovery on 24 January 1801 in letters to only two fellow astronomers, his compatriot Barnaba Oriani of Milan and Bode in Berlin. He reported it as a comet but "since its movement
13254-404: The group of bright spots to its east, Vinalia Faculae. Occator possesses a pit 9–10 km wide, partially filled by a central dome. The dome post-dates the faculae and is likely due to freezing of a subterranean reservoir, comparable to pingos in Earth's Arctic region. A haze periodically appears above Cerealia, supporting the hypothesis that some sort of outgassing or sublimating ice formed
13395-594: The inner Solar System. Their orbits are perturbed by the gravity of other bodies in the Solar System and by the Yarkovsky effect . Significant populations include: The majority of known asteroids orbit within the asteroid belt between the orbits of Mars and Jupiter , generally in relatively low- eccentricity (i.e. not very elongated) orbits. This belt is estimated to contain between 1.1 and 1.9 million asteroids larger than 1 km (0.6 mi) in diameter, and millions of smaller ones. These asteroids may be remnants of
13536-404: The largest minor planets—those massive enough to have become ellipsoidal under their own gravity. Only the largest object in the asteroid belt has been placed in this category: Ceres , at about 975 km (606 mi) across. Despite their large numbers, asteroids are a relatively recent discovery, with the first one—Ceres—only being identified in 1801. Only one asteroid, 4 Vesta , which has
13677-720: The largest potentially hazardous asteroids with a diameter of 4.5 km (2.8 mi), has two moons measuring 100–300 m (330–980 ft) across, which were discovered by radar imaging during the asteroid's 2017 approach to Earth. Near-Earth asteroids are divided into groups based on their semi-major axis (a), perihelion distance (q), and aphelion distance (Q): It is unclear whether Martian moons Phobos and Deimos are captured asteroids or were formed due to impact event on Mars. Phobos and Deimos both have much in common with carbonaceous C-type asteroids , with spectra , albedo , and density very similar to those of C- or D-type asteroids. Based on their similarity, one hypothesis
13818-422: The law was a coincidence. The early observers were able to calculate the size of Ceres only to within an order of magnitude . Herschel underestimated its diameter at 260 km (160 mi) in 1802; in 1811, German astronomer Johann Hieronymus Schröter overestimated it as 2,613 km (1,624 mi). In the 1970s, infrared photometry enabled more accurate measurements of its albedo , and Ceres's diameter
13959-512: The law was a coincidence. Piazzi named the newly discovered object Ceres Ferdinandea, "in honor of the patron goddess of Sicily and of King Ferdinand of Bourbon ". Three other asteroids ( 2 Pallas , 3 Juno , and 4 Vesta ) were discovered by von Zach's group over the next few years, with Vesta found in 1807. No new asteroids were discovered until 1845. Amateur astronomer Karl Ludwig Hencke started his searches of new asteroids in 1830, and fifteen years later, while looking for Vesta, he found
14100-416: The majority of asteroids. The four largest asteroids constitute half the mass of the asteroid belt. Ceres is the only asteroid that appears to have a plastic shape under its own gravity and hence the only one that is a dwarf planet . It has a much higher absolute magnitude than the other asteroids, of around 3.32, and may possess a surface layer of ice. Like the planets, Ceres is differentiated: it has
14241-416: The mass of the Moon . It is close to being in hydrostatic equilibrium , but some deviations from an equilibrium shape have yet to be explained. Regardless, Ceres is the only widely accepted dwarf planet with an orbital period less than that of Neptune. Modelling has suggested Ceres's rocky material is partially differentiated , and that it may possess a small core , but the data is also consistent with
14382-479: The most accepted hypothesis is that these electrons are being accelerated by collisions between the solar wind and a tenuous water vapour exosphere. Bow shocks like these could also be explained by a transient magnetic field, but this is considered less likely, as the interior of Ceres is not thought to be sufficiently electrically conductive. Ceres' thin exosphere is continuously replenished through exposure of water ice patches by impacts, water ice diffusion through
14523-514: The most part to the classical asteroids: objects of the asteroid belt , Jupiter trojans , and near-Earth objects . For almost two centuries after the discovery of Ceres in 1801, all known asteroids spent most of their time at or within the orbit of Jupiter, though a few, such as 944 Hidalgo , ventured farther for part of their orbit. Starting in 1977 with 2060 Chiron , astronomers discovered small bodies that permanently resided further out than Jupiter, now called centaurs . In 1992, 15760 Albion
14664-417: The most water of any body in the inner Solar System after Earth, and the likely brine pockets under its surface could provide habitats for life. Unlike Europa or Enceladus, it does not experience tidal heating , but it is close enough to the Sun, and contains enough long-lived radioactive isotopes, to preserve liquid water in its subsurface for extended periods. The remote detection of organic compounds and
14805-503: The number—e.g. (433) Eros—but dropping the parentheses is quite common. Informally, it is also common to drop the number altogether, or to drop it after the first mention when a name is repeated in running text. In addition, names can be proposed by the asteroid's discoverer, within guidelines established by the International Astronomical Union. The first asteroids to be discovered were assigned iconic symbols like
14946-436: The objects of the asteroid belt , lying between the orbits of Mars and Jupiter , is estimated to be (2394 ± 6) × 10 kg , ≈ 3.25% of the mass of the Moon. Of this, Ceres comprises 938 × 10 kg , about 40% of the total. Adding in the next three most massive objects, Vesta (11%), Pallas (8.5%), and Hygiea (3–4%), brings this figure up to a bit over 60%, whereas the next seven most-massive asteroids bring
15087-401: The observed viscous relaxation could not occur. An unexpectedly large number of Cererian craters have central pits, perhaps due to cryovolcanic processes; others have central peaks. Hundreds of bright spots (faculae) have been observed by Dawn , the brightest in the middle of 80 km (50 mi) Occator Crater . The bright spot in the centre of Occator is named Cerealia Facula, and
15228-463: The observer has only found an apparition, which gets a provisional designation , made up of the year of discovery, a letter representing the half-month of discovery, and finally a letter and a number indicating the discovery's sequential number (example: 1998 FJ 74 ). The last step is sending the locations and time of observations to the Minor Planet Center , where computer programs determine whether an apparition ties together earlier apparitions into
15369-448: The ones so far discovered are larger than traditional comet nuclei . Other recent observations, such as the analysis of the cometary dust collected by the Stardust probe, are increasingly blurring the distinction between comets and asteroids, suggesting "a continuum between asteroids and comets" rather than a sharp dividing line. In 2006, the IAU created the class of dwarf planets for
15510-538: The ones traditionally used to designate the planets. By 1852 there were two dozen asteroid symbols, which often occurred in multiple variants. In 1851, after the fifteenth asteroid, Eunomia , had been discovered, Johann Franz Encke made a major change in the upcoming 1854 edition of the Berliner Astronomisches Jahrbuch (BAJ, Berlin Astronomical Yearbook ). He introduced a disk (circle),
15651-566: The origin of Earth's moon. Asteroids vary greatly in size, from almost 1000 km for the largest down to rocks just 1 meter across, below which an object is classified as a meteoroid . The three largest are very much like miniature planets: they are roughly spherical, have at least partly differentiated interiors, and are thought to be surviving protoplanets . The vast majority, however, are much smaller and are irregularly shaped; they are thought to be either battered planetesimals or fragments of larger bodies. The dwarf planet Ceres
15792-455: The path of Ceres and sent his results to von Zach. On 31 December 1801, von Zach and fellow celestial policeman Heinrich W. M. Olbers found Ceres near the predicted position and thus recovered it. At 2.8 AU from the Sun, Ceres appeared to fit the Titius–Bode law almost perfectly; however, Neptune, once discovered in 1846, was 8 AU closer than predicted, leading most astronomers to conclude that
15933-419: The path of Ceres within a few weeks and sent his results to von Zach. On 31 December 1801, von Zach and fellow celestial policeman Heinrich W. M. Olbers found Ceres near the predicted position and continued to record its position. At 2.8 AU from the Sun, Ceres appeared to fit the Titius–Bode law almost perfectly; when Neptune was discovered in 1846, eight AU closer than predicted, most astronomers concluded that
16074-442: The planet Venus, but with a break in the circle. It had various minor graphic variants, including a reversed form [REDACTED] typeset as a 'C' (the initial letter of the name Ceres ) with a plus sign. The generic asteroid symbol of a numbered disk, ①, was introduced in 1867 and quickly became the norm. The categorisation of Ceres has changed more than once and has been the subject of some disagreement. Bode believed Ceres to be
16215-515: The porous ice crust and proton sputtering during solar activity. The rate of this vapour diffusion scales with grain size and is heavily affected by a global dust mantle consisting of an aggregate of approximately 1 micron particles. Exospheric replenishment through sublimation alone is very small, with the current outgassing rate being only 0.003 kg/s. Various models of an extant exosphere have been attempted including ballistic trajectory, DSMC , and polar cap numerical models. Results showed
16356-459: The presence of water mixed with 20% carbon by mass in its near surface could provide conditions favourable to organic chemistry. Of the biochemical elements, Ceres is rich in carbon , hydrogen , oxygen and nitrogen , but phosphorus has yet to be detected, and sulfur, despite being suggested by Hubble UV observations, was not detected by Dawn . When in opposition near its perihelion , Ceres can reach an apparent magnitude of +6.7. This
16497-427: The same birth cloud as Mars. Another hypothesis is that Mars was once surrounded by many Phobos- and Deimos-sized bodies, perhaps ejected into orbit around it by a collision with a large planetesimal . The high porosity of the interior of Phobos (based on the density of 1.88 g/cm , voids are estimated to comprise 25 to 35 percent of Phobos's volume) is inconsistent with an asteroidal origin. Observations of Phobos in
16638-404: The surface has preserved craters almost 300 km (200 mi) in diameter indicates that the outermost layer of Ceres is roughly 1000 times stronger than water ice. This is consistent with a mixture of silicates , hydrated salts and methane clathrates , with no more than 30% water ice by volume. Gravity measurements from Dawn have generated three competing models for Ceres's interior. In
16779-457: The surface in hundreds of locations causing "bright spots", including those in Occator Crater. The active geology of Ceres is driven by ice and brines. Water leached from rock is estimated to possess a salinity of around 5%. Altogether, Ceres is approximately 50% water by volume (compared to 0.1% for Earth) and 73% rock by mass. Ceres's largest craters are several kilometres deep, inconsistent with an ice-rich shallow subsurface. The fact that
16920-622: The surface temperature changes rapidly) and meteoritic impacts. Their maximum age is estimated to be 150 million years, much shorter than the lifetime of boulders on Vesta. Although Ceres lacks plate tectonics , with the vast majority of its surface features linked either to impacts or to cryovolcanic activity, several potentially tectonic features have been tentatively identified on its surface, particularly in its eastern hemisphere. The Samhain Catenae, kilometre-scale linear fractures on Ceres's surface, lack any apparent link to impacts and bear
17061-424: The surface would leave a deposit of hydrated particulates perhaps twenty metres thick. The range of the extent of differentiation is consistent with the data, from a large, 360 km (220 mi) core of 75% chondrules and 25% particulates and a mantle of 75% ice and 25% particulates, to a small, 85 km (55 mi) core consisting nearly entirely of particulates and a mantle of 30% ice and 70% particulates. With
17202-562: The surface. Kerwan too shows evidence of the effects of liquid water due to impact-melting of subsurface ice. A 2018 computer simulation suggests that cryovolcanoes on Ceres, once formed, recede due to viscous relaxation over several hundred million years. The team identified 22 features as strong candidates for relaxed cryovolcanoes on Ceres's surface. Yamor Mons, an ancient, impact-cratered peak, resembles Ahuna Mons despite being much older, due to it lying in Ceres's northern polar region, where lower temperatures prevent viscous relaxation of
17343-496: The three most successful asteroid-hunters at that time, on a commemorative medallion marking the event. In 1891, Max Wolf pioneered the use of astrophotography to detect asteroids, which appeared as short streaks on long-exposure photographic plates. This dramatically increased the rate of detection compared with earlier visual methods: Wolf alone discovered 248 asteroids, beginning with 323 Brucia , whereas only slightly more than 300 had been discovered up to that point. It
17484-488: The three-layer model, Ceres is thought to consist of an outer, 40 km (25 mi) thick crust of ice, salts and hydrated minerals and an inner muddy " mantle " of hydrated rock, such as clays, separated by a 60 km (37 mi) layer of a muddy mixture of brine and rock. It is not possible to tell if Ceres's deep interior contains liquid or a core of dense material rich in metal, but the low central density suggests it may retain about 10% porosity . One study estimated
17625-439: The total number ranges in the millions or more, depending on the lower size cutoff. Over 200 asteroids are known to be larger than 100 km, and a survey in the infrared wavelengths has shown that the asteroid belt has between 700,000 and 1.7 million asteroids with a diameter of 1 km or more. The absolute magnitudes of most of the known asteroids are between 11 and 19, with the median at about 16. The total mass of
17766-449: The total up to 70%. The number of asteroids increases rapidly as their individual masses decrease. The number of asteroids decreases markedly with increasing size. Although the size distribution generally follows a power law , there are 'bumps' at about 5 km and 100 km , where more asteroids than expected from such a curve are found. Most asteroids larger than approximately 120 km in diameter are primordial (surviving from
17907-490: The traps, hopping an average of three times before escaping or being trapped. Dawn , the first spacecraft to orbit Ceres, determined that the north polar axis points at right ascension 19 h 25 m 40.3 s (291.418°), declination +66° 45' 50" (about 1.5 degrees from Delta Draconis ), which means an axial tilt of 4°. This means that Ceres currently sees little to no seasonal variation in sunlight by latitude. Gravitational influence from Jupiter and Saturn over
18048-706: The two Lagrangian points of stability, L 4 and L 5 , which lie 60° ahead of and behind the larger body. In the Solar System, most known trojans share the orbit of Jupiter . They are divided into the Greek camp at L 4 (ahead of Jupiter) and the Trojan camp at L 5 (trailing Jupiter). More than a million Jupiter trojans larger than one kilometer are thought to exist, of which more than 7,000 are currently catalogued. In other planetary orbits only nine Mars trojans , 28 Neptune trojans , two Uranus trojans , and two Earth trojans , have been found to date. A temporary Venus trojan
18189-413: The word "planet" had yet to be precisely defined . In the 1950s, scientists generally stopped considering most asteroids as planets, but Ceres sometimes retained its status after that because of its planet-like geophysical complexity. Then, in 2006, the debate surrounding Pluto led to calls for a definition of "planet", and the possible reclassification of Ceres, perhaps even its general reinstatement as
18330-405: The years between the acceptance of heliocentrism in the 18th century and the discovery of Neptune in 1846, several astronomers argued that mathematical laws predicted the existence of a hidden or missing planet between the orbits of Mars and Jupiter . In 1596, theoretical astronomer Johannes Kepler believed that the ratios between planetary orbits would conform to " God's design " only with
18471-407: Was a comet: The light was a little faint, and of the colour of Jupiter , but similar to many others which generally are reckoned of the eighth magnitude . Therefore I had no doubt of its being any other than a fixed star. [...] The evening of the third, my suspicion was converted into certainty, being assured it was not a fixed star. Nevertheless before I made it known, I waited till the evening of
18612-489: Was available for this to occur for Deimos. Capture also requires dissipation of energy. The current Martian atmosphere is too thin to capture a Phobos-sized object by atmospheric braking. Geoffrey A. Landis has pointed out that the capture could have occurred if the original body was a binary asteroid that separated under tidal forces. Phobos could be a second-generation Solar System object that coalesced in orbit after Mars formed, rather than forming concurrently out of
18753-438: Was calculated and registered within that specific year. For example, the first two asteroids discovered in 1892 were labeled 1892A and 1892B. However, there were not enough letters in the alphabet for all of the asteroids discovered in 1893, so 1893Z was followed by 1893AA. A number of variations of these methods were tried, including designations that included year plus a Greek letter in 1914. A simple chronological numbering system
18894-507: Was determined to within ten per cent of its true value of 939 km (583 mi). Piazzi's proposed name for his discovery was Ceres Ferdinandea : Ceres after the Roman goddess of agriculture , whose earthly home, and oldest temple, lay in Sicily; and Ferdinandea in honour of Piazzi's monarch and patron, King Ferdinand III of Sicily . The latter was not acceptable to other nations and
19035-402: Was discovered in 1802, Herschel coined the term asteroid ("star-like") for these bodies, writing that "they resemble small stars so much as hardly to be distinguished from them, even by very good telescopes". In 1852 Johann Franz Encke , in the Berliner Astronomisches Jahrbuch , declared the traditional system of granting planetary symbols too cumbersome for these new objects and introduced
19176-534: Was discovered, the first object beyond the orbit of Neptune (other than Pluto ); soon large numbers of similar objects were observed, now called trans-Neptunian object . Further out are Kuiper-belt objects , scattered-disc objects , and the much more distant Oort cloud , hypothesized to be the main reservoir of dormant comets. They inhabit the cold outer reaches of the Solar System where ices remain solid and comet-like bodies exhibit little cometary activity; if centaurs or trans-Neptunian objects were to venture close to
19317-546: Was dropped. Before von Zach's recovery of Ceres in December 1801, von Zach referred to the planet as Hera , and Bode referred to it as Juno . Despite Piazzi's objections, those names gained currency in Germany before the object's existence was confirmed. Once it was, astronomers settled on Piazzi's name. The adjectival forms of Ceres are Cererian and Cererean , both pronounced / s ɪ ˈ r ɪər i ə n / . Cerium ,
19458-450: Was established in 1925. Currently all newly discovered asteroids receive a provisional designation (such as 2002 AT 4 ) consisting of the year of discovery and an alphanumeric code indicating the half-month of discovery and the sequence within that half-month. Once an asteroid's orbit has been confirmed, it is given a number, and later may also be given a name (e.g. 433 Eros ). The formal naming convention uses parentheses around
19599-534: Was known that there were many more, but most astronomers did not bother with them, some calling them "vermin of the skies", a phrase variously attributed to Eduard Suess and Edmund Weiss . Even a century later, only a few thousand asteroids were identified, numbered and named. In the past, asteroids were discovered by a four-step process. First, a region of the sky was photographed by a wide-field telescope or astrograph . Pairs of photographs were taken, typically one hour apart. Multiple pairs could be taken over
19740-447: Was needed to categorize or name asteroids. In 1852, when de Gasparis discovered the twentieth asteroid, Benjamin Valz gave it a name and a number designating its rank among asteroid discoveries, 20 Massalia . Sometimes asteroids were discovered and not seen again. So, starting in 1892, new asteroids were listed by the year and a capital letter indicating the order in which the asteroid's orbit
19881-581: Was searching for "the 87th [star] of the Catalogue of the Zodiacal stars of Mr la Caille ", but found that "it was preceded by another". Instead of a star, Piazzi had found a moving starlike object, which he first thought was a comet. Piazzi observed Ceres twenty-four times, the final sighting occurring on 11 February 1801, when illness interrupted his work. He announced his discovery on 24 January 1801 in letters to two fellow astronomers, his compatriot Barnaba Oriani of Milan and Bode in Berlin . He reported it as
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