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| mean_radius = 〔 | surface_area = 〔Calculated based on the known parameters〕 | volume = 〔 | mass=〔 0.0128 Moons | density=〔(Dawn explores Ceres: Results from the survey orbit (cached version) )〕 |surface_grav = m/s2〔 0.029 ''g'' | escape_velocity= km/s〔 | sidereal_day = | rot_velocity= 〔 | right_asc_north_pole = 294.18°〔(【引用サイトリンク】url=http://naif.jpl.nasa.gov/pub/naif/DAWN/kernels/pck/dawn_ceres_v05.tpc )〕 | declination = 66.764°〔 | axial_tilt = 4°〔 | albedo= (V-band geometric)〔 | temperatures = yes | temp_name1 = Kelvin | min_temp_1 = ? | mean_temp_1 = ≈ 168 K | max_temp_1 = 235 K〔 | spectral_type=C〔 | magnitude = 6.64〔 to 9.34〔 | abs_magnitude =〔 | angular_size = 0.854″ to 0.339″ }} Ceres (; minor-planet designation: 1 Ceres) is the largest object in the asteroid belt, which lies between the orbits of Mars and Jupiter. Its diameter is approximately ,〔 making it the largest of the minor planets within the orbit of Neptune. The thirty-third largest known body in the Solar System, it is the only one identified orbiting entirely within the orbit of Neptune that is a dwarf planet. Composed of rock and ice, Ceres is estimated to comprise 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. 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 discovered, by Giuseppe Piazzi at Palermo on 1 January 1801. It was originally considered a planet, but was reclassified as an asteroid in the 1850s when many other objects in similar orbits were discovered. Ceres appears to be differentiated into a rocky core and icy mantle, and may harbor 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.〔NASA Science News: (Water Detected on Dwarf Planet Ceres ), by Production editor: Dr. Tony Phillips | Credit: Science@NASA (22 January 2014)〕 This was unexpected, because large bodies in the asteroid belt do not typically emit vapor, a hallmark of comets. The robotic NASA spacecraft ''Dawn'' entered orbit around Ceres on 6 March 2015.〔(【引用サイトリンク】url=http://www.nasa.gov/jpl/dawn/dawn-spacecraft-begins-approach-to-dwarf-planet-ceres/ )〕 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 (or high-albedo features) inside a crater (different from the bright spots observed in earlier Hubble images,) 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. On 11 May 2015, NASA released a higher resolution image showing that, instead of one or two spots, there are actually several. In October 2015, NASA released a true color portrait of Ceres made by ''Dawn''. ==History== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ceres (dwarf planet)」の詳細全文を読む スポンサード リンク
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