Dawn’s First Look At Asteroid Vesta

The 8-day-old moon lights the sky. Photo: Bob King

After a long day, it sure felt great to walk in the humid moonlight last night. Recent rains have kept the frogs happy and singing. They were joined by the high-pitched trill of an American toad, the first of the season for me. The shadows cast the first quarter moon are softer than those at full. A few clouds strode lazily across the moon’s face. No hurry. The quiet mood returned my mind to the present moment where it’s most at home.

This image shows Vesta in front of a spectacular background of stars on May 3. Since Vesta is so bright, it outshines its starry background. Dawn team members corrected the resulting exaggerated size of Vesta by superimposing a short exposure image of the target asteroid, showing its true size. Vesta is the small, bright pearl in the middle of the image. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

The Dawn space probe returned its first picture of the 330-mile asteroid Vesta this week. As described in this earlier blog, Dawn will be photographing Vesta to keep itself on course until it’s inserted into orbit around the asteroid on July 16. It doesn’t look like much yet, but the spacecraft was close enough – 750,000 miles – to show its shape. You can see this by comparing it with the stars in the background in the close-up image at right.

In this larger, cropped photo, you can just make out Vesta's shape. Credit: NASA

After Ceres (568 miles), Vesta is the second most massive object in the asteroid belt. The belt, located between Mars and Jupiter, contains millions of asteroids from Ceres-size down to small pebbles. Scientists estimate that if you could combine all the 3-foot and larger bodies into one giant one, it would still only be 800-930 miles across or less than half the size of the moon. Unlike the icy comets, most asteroids are composed of a mix of stony materials or silicates and metal. Were it not for the disturbing gravity of nearby Jupiter, an additional small planet would likely be orbiting between Mars and Jupiter instead of the broken and pummeled proto-planetary debris we call asteroids.

Back on February 14, 2000, the NEAR Shoemaker space probe was inserted into orbit around the 21-mile long asteroid Eros, the first asteroid orbital mission ever. Besides studying and photographing its surface rocks and craters, NEAR also made a cool video of a full rotation of the asteroid.

Movie made by the NEAR probe as it orbited Eros. Credit: NASA

The movie opens with a look at one of Eros’ battered ends and a sweep over the saddle-shaped depression named Himeros. The sequence then includes a view of Shoemaker Regio – the large boulder patch beside Himeros – before swinging over the opposite end and providing a stunning view of a sunset inside Psyche, the asteroid’s large, 5-kilometer (3-mile) impact crater. The movie wraps up with a return to the asteroid’s heavily cratered tip. Seeing it whets the appetite for Dawn will bring.

The NEAR Shoemaker craft was brought to a controlled, soft landing on Eros on February 12, 2000. On its descent, it snapped closeup photos of the rocky surface before touchdown. Last contact with the craft was two weeks later after which it succombed to the extreme temperatures of this airless world. It rests there to this day.