Minor planet Ceres (15)

Astronomical specifications: Discovery   Orbital characteristics: Distance from Sun  413,700,000 km (2.766 AU) Aphelion   (106 km) Perihelion   (106 km) Inclination  10.587 deg Eccentricity  0.080 Orbital periode rond Sun  4.599 years Mean Orbital speed  17.882 km/s Inclination to Sun equator  10.587 deg Axial tilt  4 deg Number of moons  0 Physical characteristics: Dimensions   km Radius  471 km Surface area  2,800,000 km² Volume  4.37 x 108 km Mass  9.5 x 1020 kg Mean Density  2.08 g/cm³ Equatorial surface gravity  0.27 m/s² Escape velocity  0.51 km/s Rotation period  0.3781 days Surface temperature  167 K Atmospheric composition  H2O, O2

Ceres compared to asteroids visited to date, including Vesta, Dawn′s mapping target in 2011. Image by NASA/ESA/JAXA. Compiled by Paul Schenck.

Descriptions:

• Discovered on New Years′ Day, Jan. 1, 1801 by Giuseppe Piazzi of Italy. It′s been alternately classified as a planet, asteroid and more recently as a dwarf planet. Ceres is the largest object in the asteroid belt - the strip of solar system real estate between Mars and Jupiter.
  On March 6, 2015, NASA's Dawn spacecraft will arrive at Ceres, marking the first time that a spacecraft has ever orbited two solar system targets.
• When the Dawn mission was in its planning stages, Ceres was considered an asteroid. But in 2006, a year before the mission launched, the International Astronomical Union formed a new class of solar system objects known as dwarf planets, and since by definition a dwarf planet is spherical and travels in an orbit around the Sun, Ceres fit that definition perfectly.
• Of course, Ceres is bigger (it′s the biggest object in the Asteroid Belt) and more spherical than the other asteroids. When it comes right down to it, Ceres doesn′t look much like an asteroid at all!
• Ceres is most similar in size to several of Saturn′s icy moons and may be similar internally as well, being composed of 25% water ice by mass.
• And water is one of the most interesting and mysterious aspects of Ceres. A year ago, the Herschel space telescope discovered water vapor around Ceres, and the vapor could be emanating from water plumes — much like those that are on Saturn′s moon Enceladus – or it could be from cryovolcanism from geysers or icy volcano.
• Some scientists also think Ceres may have an ocean and possibly an atmosphere, which makes Dawn′s arrival at Ceres in March 2015 one of the most exciting planetary events of 2015, in addition to New Horizon′s arrival at Pluto.
  
  

  Comparison of HST and Dawn FC images of Ceres taken nearly 11 years apart. Credit: NASA.

  
  
• There′s a big white spot on Ceres and we don′t know what it is. We′ve known about the white spot since the Hubble Space Telescope first captured images of it in 2003 and 2004, and in subsequent images taken by Hubble, the spot remains visible. Now, in images released Jan 13, 2015 from the Dawn spacecraft, currently on approach to Ceres, the spot remains. In the animated image, above, the spot almost seems to glint in the sunlight.
• One of the most anticipated aspects the Dawn spacecraft being in orbit around Ceres HAS to be finding out what this spot is. It could be ice, it could be a cryovolcano or geysers, or it could be something else. But we do know fairly certain that it is a real feature and not an image artifact, since it shows up in most of the recent Hubble images and now the Dawn images.
• Planetary scientists have long suspected that water ice may be buried under Cere’s crust. A few things point to subsurface ice: the density of Ceres is less than that of the Earth′s crust, and because the surface bears spectral evidence of water-bearing minerals. Scientists estimate that if Ceres were composed of 25 percent water, it may have more water than all the fresh water on Earth. Ceres′ water, unlike Earth′s, would be in the form of water ice and located in the mantle, which wraps around the asteroid′s solid core.
• And then last year (2014), the Herschel space telescope discovered water vapor around Ceres, and the vapor could be emanating from water plumes — much like those that are on Saturn′s moon Enceladus – or it could be from cryovolcanism from geysers or icy volcanoes. Without huge a planet or satellite nearby tugging on it, the mechanism for how Ceres is active is also intriguing.

Missions to Ceres: