Spectacular Photos of Two of the Largest Known Asteroids!

The Hubble Space Telescope has recently sent some very impressive pictures of two of the largest known asteroids, showing the craters and other spectacular features on the two cosmic boulders, that will soon be explored in detail by NASA's Dawn spacecraft.

Hubble is a telescope in orbit around the Earth, named after astronomer Edwin Hubble. Its position outside the Earth's atmosphere provides significant advantages over ground based telescopes - images are not blurred by the atmosphere, there is no background light scattered from the atmosphere and the Hubble can observe in ultra-violet light that is absorbed by the ozone layer.

Ceres is the largest of the two, and it's the smallest of the three dwarf planets, originally classified as a planet and later as the largest and first discovered asteroid. It's the only one located in the main asteroid belt, it's round like a planet, and 590 miles (950 kilometers) wide.

About the size of Texas, it alone concentrates about a third of the estimated total mass of the asteroid belt expanding between Mars and Jupiter. There are some indications that the surface of Ceres is relatively warm and that it may have a tenuous atmosphere and frost.

Vesta, the other target, is irregularly shaped and about 330 miles (530 kilometers) wide-about the size of Arizona. It's the second most massive object in the asteroid belt with a mean diameter of about 530 km (around 330 miles) and an estimated mass 9% the mass of the entire asteroid belt.

This asteroid is believed to consist of a metallic iron-nickel core, an overlying rocky olivine mantle, with a surface crust and the most prominent feature on its surface is an enormous crater 460 km (283 miles) in diameter centered near the south pole. The actual diameter of the crater is 80 percent that of the entire asteroid.

The images are helping astronomers plan for the Dawn spacecraft's tour of these hefty asteroids, a NASA mission that will send the Dawn spacecraft, a robotic space probe, to the asteroid belt, to study Ceres and Vesta. This will be the first spacecraft to enter into orbit around two different planetary bodies, other than the Earth and Moon and the first to visit the largest asteroid.