June 13, 2011 at 4:08 PM ET
The team behind NASA’s Dawn probe has released a video showing the asteroid Vesta spinning in space with a mysterious shadowy spot on its surface. It's really just the beginning of a weeks-long stream of images climaxing with Dawn's rendezvous with Vesta next month.
Dawn has been en route to Vesta for almost four years, but the $357 million mission is just now starting to get good. When the 5.4-foot-long (1.6-meter-long) spacecraft enters orbit on July 16, it will mark the first time any spacecraft has come so close to an asteroid so big. Earlier probes have landed on smaller asteroids, during NASA's NEAR-Shoemaker mission to Eros in 2001 and Japan's Hayabusa sample-return mission to Itokawa, which ended last year. But with a mean diameter of 329 miles (529 kilometers), Vesta is so big that some astronomers have wondered whether it ought to be classified as a dwarf planet.)
In terms of mass, Vesta is second only to the dwarf planet Ceres in the asteroid belt. Dawn is due to spend a year studying Vesta, and then will move on to a rendezvous with Ceres in 2015.
Right now, Dawn is about 170,500 miles (274,400 kilometers) from Vesta and closing in at a speed of 370 mph (170 meters per second). The images released today roughly match the best pictures previously taken of the asteroid by the Hubble Space Telescope. Twenty pictures, taken for navigation purposes over the course of a half-hour on June 1, were assembled in sequence to create the video you see above. One of the most notable features is a dark spot that rolls across the field of view from left to right.
"Like strangers in a strange land, we're looking for familiar landmarks," the University of Maryland's Jian-Yang Li, a member of the Dawn science team, said in a news release from NASA's Jet Propulsion Laboratory. "The shadowy spot is one of those — it appears to match a feature, known as 'Feature B,' from images of Vesta taken by NASA's Hubble Space Telescope."
The images also give you a sense of Vesta's irregular shape, which is due to a huge crater at the asteroid's south pole.
All these features will come into sharper focus in the weeks leading up to the rendezvous. NASA says it will be releasing images from Dawn's approach on a weekly basis, which should come as a relief to planetary scientists and space fans. For weeks they've been urging the Dawn team to release more such imagery, and now Vesta is finally ready for its close-up.
Update for 5:30 p.m. ET: I had Dawn's position with respect to Ceres and Vesta scrambled up for a little while, but now I have the correct current figures.
More about asteroids and other worlds:
You can connect with the Cosmic Log community by "liking" the log's Facebook page or following @b0yle on Twitter. Also, give a look to "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.