NASA’s Dawn spacecraft will enter orbit around the second most massive (but third largest) asteroid in the asteroid belt at around 10 pm Pacific Daylight Time Friday July 15. It will stay in orbit around Vesta for about a year and then move on to orbit the largest asteroid, Ceres. This demanding mission profile is made possible by using ion propulsion.
Vesta
Dimensions: About 578 by 560 by 458 kilometers (359 by 348 by 285 miles) – about the length of Arizona
Rotation: Once every 5 hours, 20 minutes
Composition: Rocky
Ceres
Size: 975 by 909 kilometers (606 by 565 miles)
Rotation: Once every 9 hours, 4.5 minutes
Composition: Believed to have large quantities of ice
