The Dawn Space Probe

The Hubble Space Telescope, using the Wide Field Planetary Camera 2, has provided pictures of two of the largest known asteroidsCeres and Vesta. These images are to be used in order to plan closer observations by the Dawn spacecraft, a robotic probe due for launch July 7, 2007, between 4:09:31 and 4:36:22 p.m. EDT. This launch is highly important as it will mark the first time a NASA scientific mission has used ion propulsion and the first to orbit two planetary bodies in a single flight.

The mission, requiring eight years to complete the task, is designed to get a closer look at the two bodies, during which the probe will travel 3.2 billion miles. Dawn will pass Mars in March 2009 for a gravity-assist to increase the speed, arriving at Vesta in October 2011 and leaving the asteroids orbit in April 2012 . The probe will arrive at Ceres in February 2015, with July 2015 being the projected end of the mission unless the spacecraft is still capable of traveling to other asteroids and undertaking other operations.

Ceres, the larger of the two bodies, is 590 miles across with a rounded, planet-like shape, and was initially considered a planet after its discovery in 1801. Later reclassified as an asteroid, it has now been designated a dwarf planet under the International Astronomical Unions new planetary definition. About the size of Texas, the dwarf planet comprises much of the mass of the asteroid belt between Mars and Jupiter, some 30% to 40%. The roundness of Ceres indicates the possibility of layers, as in the Earths interior, surrounding a rocky core. Its presumed icy beginning even suggests the possibility of subsurface water.

The smaller of the two bodies, Vesta, is not as rounded as Ceres and is 330 miles across or about the size of Arizona. An enormous crater discovered on the asteroids Southern Hemisphere, is 285 miles across and the collision that created it would have knocked out many smaller bodies called vestoids. The images of Vesta reveal different colors, denoting differences in the chemical composition of the surface, possibly the result of volcanism. While Ceres beginning is thought to have been wet and cold, Vestas genesis is considered to have been hot and dry, producing volcanic activity both above and below the surface. Both Ceres and Vesta are considered proto planets, having the potential at one time to become planets, and are thought to be over 4.5 billion years old. As proto planets, they could provide important information about the earliest stages of the solar systems formation.

Nancy Houser, author of "A Mars Odyssey," is a freelance writer and illustrator of 30 years. Living in Central Nebraska running a dog rescue, she fills her leisurely time with 13 grandchildren and watching the skies.

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