Here, the 976-kilometer-wide / 606-mile-wide main belt asteroid / protoplanet / dwarf planet 1 Ceres is seen by the approaching Dawn spacecraft from a distance of 1.2 million kilometers / 745,000 miles, on December 1, 2014. Dawn begins its approach phase toward Ceres on December 26 and will arrive at Ceres in March, 2015.
These are test images and 1 Ceres appears only nine pixels wide at this point, perfect for a far-encounter camera calibration.
The main image shows 1 Ceres overexposed with a few background stars within the constellation of Ophiuchus the Serpent Bearer.
1 Ceres is the largest and most massive of all of the members of the main asteroid belt between the orbits of Mars and Jupiter. 1 Ceres orbits the sun at an average distance of 414 million kilometers / 257 million miles once every 4 years and 218 days.
1 Ceres appears to have a density of 2.09 g/cm3, suggesting 70% rock and 30% ice in composition, very similar ratios to KBOs / Dwarf planets Eris and Pluto.
There have been suggestions that 1 Ceres did indeed originate in the Kuiper Belt then was ejected inwards and was sent into an orbit within the asteroid belt by Jupiter. Myself, I do not think that is the case. I think 1 Ceres formed close to the current orbit, when the infant sun was approximatelyt 30% dimmer than now, so that region was much colder than now, and that Jupiter prevented 1 Ceres from forming into a fully-fledged planet. Jupiter may also had stunted the growth of Mars and asteroids / protoplanets 2 Pallas, 4 Vesta and 10 Hygeia.
1 Ceres rotates once ever 9 hours 4 minutes in a prograde west to east direction.
The surface gravity of 1 Ceres is 0.029 or 1/34th that on Earth.
Andrew R. Brown, an avid follower of the space program, writes frequently about space topics for EarthSky. Over several years, he has also suggested observations that were carried out by imaging teams of some space missions. He has lives in Ashford, Kent, United Kingdom and works for local government, Kent County Council.