Dawn Approaches the Asteroid Belt

A new mission to explore the largest asteroids in the Solar System.

On September 27, 2007, NASA launched the Dawn spacecraft on a mission that will take it into the asteroid belt, where it will study two of the largest planetesimals in orbit between Mars and Jupiter, Ceres and Vesta. Dawn is so named because it will be observing objects thought to have existed since the dawn of the Solar System.

"Asteroid" was first coined by William Herschel and means "star-like." Ceres was the first asteroid discovered in 1801 by Guiseppe Piazzi and the largest known, with a diameter of approximately 950 kilometers. Since no spacecraft has visited Ceres, its size estimate is determined by combining data from various telescope observations. Ceres compares in size to Saturn's moons Tethys and Dione and might look similar to Dione, with craters and ridges, although Ceres is about 15% smaller.

Ceres has recently been added to the roster of "dwarf planets" along with Pluto—Ceres being the only one within the asteroid belt. Vesta, the first one of the Dawn mission's targets, could also be added, something that data from the space probe will help to determine.

Vesta is the second largest asteroid, with a diameter of approximately 530 kilometers. It was found in 1807 by Heinrich Wilhelm Olbers. Using Saturn's moons for scale again, Vesta compares to Enceladus or Mimas in size. ...

via Dawn Approaches the Asteroid Belt.