Claim: Ceres is a dwarf planet.

Ceres -LRB- -LSB- ˈsɪəriːz -RSB- minor-planet designation : 1 Ceres -RRB- is the largest object in the asteroid belt that lies between the orbits of Mars and Jupiter . Its diameter is approximately 945 km , making it the largest of the minor planets within the orbit of Neptune . The 33rd-largest known body in the Solar System , it is the only dwarf planet within the orbit of Neptune.Due to its eccentric orbit , the dwarf planet Pluto was also within the orbit of Neptune from 1979 to 1999 , and will be again from approximately 2227 to 2247 . Composed of rock and ice , Ceres is estimated to compose approximately one third of the mass of the entire asteroid belt . Ceres is the only object in the asteroid belt known to be rounded by its own gravity -LRB- though detailed analysis was required to exclude 4 Vesta -RRB- . From Earth , the apparent magnitude of Ceres ranges from 6.7 to 9.3 , and hence even at its brightest it is too dim to be seen with the naked eye except under extremely dark skies .   Ceres was the first asteroid to be discovered -LRB- by Giuseppe Piazzi at Palermo on 1 January 1801 -RRB- . It was originally considered a planet , but was reclassified as an asteroid in the 1850s after many other objects in similar orbits were discovered .   Ceres appears to be differentiated into a rocky core and an icy mantle , and may have a remnant internal ocean of liquid water under the layer of ice . The surface is probably a mixture of water ice and various hydrated minerals such as carbonates and clay . In January 2014 , emissions of water vapor were detected from several regions of Ceres . This was unexpected because large bodies in the asteroid belt typically do not emit vapor , a hallmark of comets .   The robotic NASA spacecraft Dawn entered orbit around Ceres on 6 March 2015 . Pictures with a resolution previously unattained were taken during imaging sessions starting in January 2015 as Dawn approached Ceres , showing a cratered surface . Two distinct bright spots -LRB- or high-albedo features -RRB- inside a crater -LRB- different from the bright spots observed in earlier Hubble images -RRB- were seen in a 19 February 2015 image , leading to speculation about a possible cryovolcanic origin or outgassing . On 3 March 2015 , a NASA spokesperson said the spots are consistent with highly reflective materials containing ice or salts , but that cryovolcanism is unlikely . However , on 2 September 2016 , NASA scientists released a paper in Science that claimed that a massive ice volcano called Ahuna Mons is the strongest evidence yet for the existence of these mysterious ice volcanoes . On 11 May 2015 , NASA released a higher-resolution image showing that , instead of one or two spots , there are actually several . On 9 December 2015 , NASA scientists reported that the bright spots on Ceres may be related to a type of salt , particularly a form of brine containing magnesium sulfate hexahydrite -LRB- MgSO4 · 6H2O -RRB- ; the spots were also found to be associated with ammonia-rich clays . In June 2016 , near-infrared spectra of these bright areas were found to be consistent with a large amount of sodium carbonate , implying that recent geologic activity was probably involved in the creation of the bright spots .   In October 2015 , NASA released a true color portrait of Ceres made by Dawn . In February 2017 , organics were reported to have been detected on Ceres in Ernutet crater -LRB- see image -RRB- .