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Ceres (dwarf planet)

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Template:Minor Planet 1 Ceres (seer'-eez (key), IPA /ˈsiːriz/, Template:Lang-la) is a dwarf planet that might also be classified as an asteroid.Its name is derived from the Roman goddess Ceres. It was discovered on January 1 1801, by Giuseppe Piazzi.With a diameter of about 950 km, Ceres is by far the largest and most massive body in the asteroid belt: it contains approximately a third of the belt's total mass.

The classification of Ceres has changed more than once. At the time of its discovery it was considered a planet, but upon the realization that it represented the first of a class of many similar bodies, it was reclassified as an asteroid for over 150 years. As the first such body to be discovered, its name was prefixed by the number 1, under the modern system of asteroid numbering. After the discovery of the trans-Neptunian object 2003 UB313, a proposition was made by the International Astronomical Union to reinstate Ceres to the status of planet along with Pluto's moon, Charon, and 2003 UB313.[1][2] This draft definition did not successfully pass, and in its place an alternate proposal came into effect as of August 24 2006, labelling Ceres a 'dwarf planet'. It is not yet clear whether dwarf planet status is, like planet status, a sole defining category, or whether dwarf planets also retain their previous minor body classifications such as "asteroid."

Name

Ceres was originally named Ceres Ferdinandea after both the mythological figure Ceres (Roman goddess of plants and motherly love) and King Ferdinand III of Sicily (also known as Ferdinand IV of Naples, and as Ferdinand I of the Two Sicilies). King Ferdinand was taking refuge in Palermo at the time, the Kingdom of Naples having been conquered by the French in 1798. The "Ferdinandea" part was not acceptable to other nations of the world and was dropped. Ceres was also called Hera for a short time in Germany.

Due to the rarity of the usage, there is no consensus as to the proper adjectival form of the name, although the nonce forms Cerian and Cerean have been used in fiction.

Discovery

Ceres was discovered by accident. Piazzi was searching for a star listed by Francis Wollaston as Mayer 87 because it was not in Mayer's zodiacal catalogue in the position given. Instead, Piazzi found a moving star-like object, which he thought at first was a comet.

Piazzi observed Ceres a total of 24 times, the final time on February 11, when illness interrupted. On January 24 1801, Piazzi announced his discovery in letters to fellow astronomers, among them his fellow countryman, Barnaba Oriani of Milan. He reported it as 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".[3] By early February Ceres was lost as it receded behind the Sun. In April, Piazzi sent his complete observations to Oriani, Bode, and Lalande in Paris. They were shortly thereafter published in the September, 1801 issue of the Monatliche Correspondenz.

Left to right: 4 Vesta, 1 Ceres, Earth's Moon

To recover the asteroid, Carl Friedrich Gauss, then only 24 years old, developed a method of orbit determination from three observations. In only a few weeks, he predicted the path of Ceres, and sent his results to Franz Xaver, Baron von Zach, the editor of the Monatliche Correspondenz. On December 31 1801, von Zach and Heinrich W. M. Olbers unambiguously confirmed the recovery of Ceres.

Status

Johann Elert Bode believed Ceres to be the "missing planet" that Johann Daniel Titius had proposed to exist between Mars and Jupiter, at a distance of 419 million km (2.8 AU) from the Sun. Ceres was assigned a planetary symbol, and remained listed as a planet in astronomy books and tables (along with 2 Pallas, 3 Juno and 4 Vesta) for about half a century until further asteroids were discovered.[4] Ceres turned out to be disappointingly small for a planet, showing no discernible disc, so Sir William Herschel coined the term "asteroid" ("star-like") to describe it.

The 2006 debate surrounding Pluto and what constitutes a 'planet' led to Ceres being considered for reclassification as a planet. An unsuccessful proposal before the International Astronomical Union for the definition of a planet would have 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 a planet". Had this resolution been adopted, this would make Ceres the fifth planet in order from the Sun.[5] Instead, the new definition of 'planet' will be "a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a ... nearly round shape, and has cleared the neighborhood around its orbit." By this definition, 1 Ceres (along with Pluto) cannot be classified as a planet.

Orbit

Orbit of Ceres (yellow) and Mars (red). Orbit of Ceres (yellow) and Mars (red).

Ceres follows an orbit between Mars and Jupiter, within the main asteroid belt, with a period of 4.6 years. The orbit is moderately inclined (i=10.6° to be compared with 7° for Mercury and 17° for Pluto) and moderately eccentric (e=0.08 to compare with 0.09 for Mars).

The diagram illustrates the orbits of Ceres (yellow) and Mars (red) as seen from the ecliptic pole (top) and from the ascending node (below). The segments of orbits below the ecliptic are plotted in darker colours. The periphelia (q) and aphelia (Q) are labelled with the date of the nearest passage. Interestingly, the perihelia of Ceres (as well as several other of the largest MBAs) and Mars are on the opposite side of the Sun.

Physical characteristics

Hubble Space Telescope images of Ceres, taken in 2003/4 with a resolution of about 30 km. The nature of the bright spot is uncertain. A movie was also made.[6]
Size comparison: the first ten asteroids profiled against Earth's Moon; Ceres is at far left.

Ceres is the largest known asteroid in the asteroid belt, which mostly lies between Mars and Jupiter. However, it is not the largest object besides the Sun, planets and their satellites, in the solar system: the Kuiper belt is known to contain larger objects, including 50000 Quaoar, 90482 Orcus, 2003 UB313, and possibly 90377 Sedna.

At certain points in its orbit, Ceres can reach a magnitude of 7.0. This is generally regarded as being just barely too dim to be seen with the naked eye, but under exceptional viewing conditions a very sharp-sighted person may be able to see the asteroid with the naked eye. The only other asteroid that can be seen with the naked eye is 4 Vesta.

Ceres is rare among asteroids in that its size and mass are sufficient to give it a nearly spherical shape: That is, it is a gravitationally relaxed equilibrium spheroid, or "planetary body". The only other known gravitationally relaxed asteroid is 4 Vesta. Other large asteroids such as 2 Pallas and 3 Juno are known to be distinctly non-spherical, while lightcurve analysis of 10 Hygiea indicates it is oblong although it appeared spheroidal in low-resolution images (presumably due to viewing angle).

With a mass of 9.5×1020 kg, Ceres comprises about a third of the estimated total 3.0±0.2×1021 kg mass of all the asteroids in the solar system[7] (note how all these amount to only about 4% of the mass of the Moon).

There are some indications that the Cererian surface is relatively warm and that it may have a tenuous atmosphere and frost. The maximum temperature with the Sun overhead was estimated from measurements to be 235 K (about -38 °C) on May 5 1991.[8] Taking into account also the heliocentric distance at the time, gives an estimated maximum of ~239 K at perihelion.

A study led by Peter Thomas of Cornell University suggests that Ceres has a differentiated interior: observations coupled with computer models suggest the presence of a rocky core overlain with an icy mantle. This mantle of thickness from 120 to 60 km could contain 200 million cubic kilometres of water, which is more than the amount of fresh water on the Earth.[9][10]

There has been some ambiguity regarding surface features on Ceres. Low resolution ultraviolet Hubble Space Telescope images taken in 1995 showed a dark spot on its surface which was nicknamed "Piazzi" in honour of the discoverer of Ceres. This was thought to be a crater. Later images with a higher resolution taken over a whole rotation with the Keck telescope using adaptive optics showed no sign of "Piazzi". However, two dark features were seen to move with the asteroid's rotation, one with a bright central region. These are presumably craters. More recent visible light Hubble Space Telescope images of a full rotation taken in 2003 and 2004 show an enigmatic white spot, the nature of which is currently unknown.[11] The dark albedo features seen with Keck are, however, not immediately recognizable in these images.

These last observations also determined that Ceres' north pole points (give or take about 5°) in the direction of right ascension 19 h 24 min, declination +59°, in the constellation Draco. This means that Ceres' axial tilt is very small (about 4±5°).[10]

Model of Ceres based on Hubble Space Telescope images from 2003 and 2004.
File:1 ceres.png
Hubble Space Telescope UV image of Ceres, taken in 1995 with a resolution of about 60 km. The "Piazzi" feature is the dark spot in the center.

Ceres was long thought to be the parent body of the "Ceres asteroid family". However, that grouping is now defunct because Ceres has been shown to be an interloper in its "own" family, and physically unrelated. The bulk of that asteroid group is now called the Gefion family.

Observations

Some notable observation milestones for Ceres include:

An occultation of a star by Ceres was observed in Mexico, Florida and across the Caribbean on November 13 1984.

Features on Ceres' surface have been telescopically imaged several times in recent years.

These include:

Radar signals from spacecraft in orbit around Mars and on its surface have been used to estimate the mass of Ceres from the tiny perturbations induced by it onto the motion of Mars.[7]

Exploration of Ceres

To date no space probes have visited Ceres. However, NASA's Dawn mission will be the first spacecraft to study Ceres. Initially the probe will visit the second most massive asteroid, 4 Vesta, for approximately six months in 2010, before arriving at Ceres in 2014 or 2015.

Namesakes

  • The chemical element Cerium (atomic number 58) was discovered in 1803 by Berzelius and Klaproth, working independently. Berzelius named the element after the asteroid. [15]
  • William Hyde Wollaston discovered palladium as early as 1802 and at first called it Ceresium. By the time he openly published his discovery in 1805, the name was already taken (by Berzelius) and he switched it to palladium in honour of 2 Pallas. [16]

Ceres in fiction

  • In Larry Niven's "Known Space" stories (1964 onward), the asteroid belt has a government based on Ceres.
  • In L. Neil Smith's novel The Venus Belt (1981), Ceres contained a large underground city, and several small settlements and stations which were connected by a network of inverted highways.
  • In Joe Haldeman's novel The Long Habit of Living (1989; British title; the U.S. title is Buying Time), Ceres is the home of a stateless society, which becomes important because of a secret research project to reinvent the Stileman rejuvenation process.
  • In the PC role-playing game Countdown to Doomsday (1990), Ceres is the location of an abandoned RAM (enemy) research base.
  • In the PC game Star Control II (1992), the destruction of Ceres Station by the invading Ur-Quan fleet signifies the defeat of the human race, leading to their subsequent enslavement.
  • In the Super Nintendo game Super Metroid (1994), the Ceres Space Colony is where Samus Aran takes the last surviving Metroid hatchling from SR-388.
  • In the PC Game Descent (1995), one of the secret levels takes place on Ceres.
  • In the PC game Terminal Velocity (1995), one of the missions involves the player destroying a machine that would cause the asteroid to crash into Earth.
  • In the fictional Warhammer 40,000 universe, the Adeptus Mechanicus renewed its alliance with the Imperium of Man in the Treaty of Ceres, following the Age of Apostasy.
  • In Ben Bova's series, the Asteroid Wars (2001 onward), a small mining base has established on Ceres.
  • In the movie The American Astronaut (2001) Ceres has a bar, called the Ceres Crossroads, where a dance contest is held.

Aspects

Stationary,
retrograde		 Opposition Distance to
Earth (AU)		 Maximum
brightness (mag)		 Stationary,
prograde		 Conjunction
to Sun
March 21 2005 May 8 2005 1.68631 7.0 June 30 2005 December 28 2005
June 26 2006 August 12 2006 1.98278 7.6 November 27 2006 March 22 2007
September 20 2007 November 9 2007 1.83690 7.2 January 1 2008 June 28 2008
January 17 2009 February 24 2009 1.58526 6.9 April 16 2009 October 31 2009
April 28 2010 June 18 2010 1.81988 7.0 August 9 2010 January 30 2011
July 31 2011 September 16 2011 1.99211 7.7 November 12 2011 April 26 2012
October 30 2012 December 17 2012 1.68842 6.7 February 4 2013 August 17 2013
March 1 2014 April 15 2014 1.63294 7.0 June 7 2014 December 10 2014
June 6 2015 July 25 2015 1.94252 7.5 September 16 2015 March 3 2016
September 1 2016 October 20 2016 1.90844 7.4 December 15 2016 June 5 2017
December 21 2017 January 31 2018 1.59531 8.8 March 20 2018 October 7 2018
April 9 2019 May 29 2019 1.74756 7.0 July 20 2019 January 14 2020
July 13 2020 August 28 2020 1.99916 7.7 October 23 2020 April 7 2021

References

  1. ^ http://www.iau2006.org/mirror/www.iau.org/iau0601/iau0601_release.html
  2. ^ http://www.latimes.com/news/science/la-sci-planets16aug16,0,3652893.story?coll=la-home-headlines?invade Proposal would increase from 9 to 12
  3. ^ Hoskin, Michael. "8. Piazzi and the Discovery of Ceres". Bode's Law and the Disovery of Ceres. Osservatorio Astronomico di Palermo, Giuseppe S. Vaiana. Retrieved 2006-08-16.
  4. ^ Hilton, J. L. (September 17, 2001). "When Did the Asteroids Become Minor Planets?". Retrieved 2006-08-16.{{cite web}}: CS1 maint: year (link)
  5. ^ http://www.spacedaily.com/reports/The_IAU_Draft_Definition_Of_Planets_And_Plutons_999.html
  6. ^ Cooke, Bill (September 12, 2005). "An icy interior for Ceres?". Astronomy. movie credit J. Parker, Southwest Research Institute
  7. ^ a b E. V. Pitjeva High-Precision Ephemerides of Planets — EPM and Determination of Some Astronomical Constants, Solar System Resarch, Vol. 39 pp. 176 (2005).
  8. ^ Cite error: The named reference Saint-Pe1993 was invoked but never defined (see the help page).
  9. ^ "Largest Asteroid Might Contain More Fresh Water than Earth". SPACE.com. 07 September 2005. Retrieved 2006-08-16. {{cite news}}: |first= missing |last= (help); Check date values in: |date= (help); Unknown parameter |lat= ignored (help)
  10. ^ a b Cite error: The named reference Thomas2005 was invoked but never defined (see the help page).
  11. ^ a b "Largest Asteroid May Be 'Mini Planet' with Water Ice". HubbleSite. September 7, 2005. Retrieved 2006-08-16.
  12. ^ "Observations reveal curiosities on the surface of asteroid Ceres". Retrieved 2006-08-16.
  13. ^ J. W. Parker et al Analysis of the first disk-resolved images of Ceres from ultraviolet observations with the Hubble Space Telescope, The Astronomical Journal, Vol. 123 pp. 549 (2002).
  14. ^ http://s1.simpload.com/10034341d7edcf588.jpg
  15. ^ "Cerium Historical Information". Retrieved 2006-08-21.
  16. ^ "Amalgamator Features 2003: 200 Years Ago". Retrieved 2006-08-21.

See also


(asteroid navigator) | 1 Ceres | Next asteroid | ...
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