If you were riding with NASA’s Dawn spacecraft, now cruising the asteroid belt between Mars and Jupiter, you would see a brightening new point of light against the starry background. This is Vesta, your immediate destination.
Dawn’s first image of Vesta, the second-largest object in the asteroid belt, still has fewer pixels than those of it taken by the Hubble Space Telescope in 2007. But this view and others enable engineers at the Jet Propulsion Laboratory in California to steer the craft into precisely the right direction for its meet-up with Vesta this summer.
Launched on Sept. 27, 2007, Dawn has been cruising through interplanetary space, gently pushed along by its ion-fueled propulsion system. It's due to brake into orbit around Vesta in mid-July and reach its lower mapping orbit in mid-August. After a year there, Dawn will work its way out of orbit and travel on to Ceres — a round, 590-mile-wide dwarf planet that probably has a rocky core and an icy surface.
Vesta is an irregular, 329-mile-wide protoplanet with an odd surface composition: it appears to be partly covered in basalts that have erupted from its interior. Dawn’s pictures, its determination of the asteroid's mass, and its spectroscopic observations of surface materials should shed light on how this body formed and how it managed to remain intact throughout solar-system history.
For the last 3½ years, engineers guided Dawn in its 1.6-billion-mile odyssey using Doppler shifts and time delays in the radio signals sent to and from the spacecraft. These signals told navigators where Dawn was in relation to Earth, but pictures from Dawn’s own cameras have finally made it possible to see the spacecraft's position in relation to its rocky first destination.
“We must now get it to go there,” says Marc Rayman, the mission’s chief engineer. “It is the same as driving a car down the street to the supermarket. You don’t just hold the steering wheel and close your eyes. You change directions and take it closer.”
As Dawn sails closer, its pictures will continue to get sharper. By the end of May, scientists hope to be receiving images 12 pixels wide. In mid-June Dawn’s pictures will probably be comparable to those of Vesta taken by Hubble. When Dawn slows into orbit, its cameras — which should by then be taking images 250 pixels wide, a resolution of 2 km per pixel — will be turned off. When they are turned on at its mapping orbit in mid-August, the resolution will be 300 m per pixel. Dawn is scheduled to dip as low as 110 miles (175 km) above the surface next year and achieve a resolution of 30 m per pixel.
I bet you can't wait to peer down on Vesta's enigmatic surface through the eyes of this robotic explorer.