Vesta and Ceres, the two largest objects in the asteroid belt, have mystified scientists for centuries. With NASA satellite Dawn on final approach to Vesta, the wait is almost over.
Courtesy of JPL / NASA
After four years and 1.7 billion miles – including two swings around the sun – NASA's Dawn spacecraft is on final approach to Vesta, an object expected to provide an unprecedented glimpse into the early years of the solar system.
Dawn, with its futuristic ion-drive engine, is just over 100,000 miles from its target – closing in at the stately pace of about 260 miles an hour, relative to Vesta's orbital speed.
The craft is scheduled to take up its orbit July 16 and spend a year at Vesta. Then it heads for a year-long visit to Ceres, slated to begin in 2015, said Robert Mase, Dawn's project manager, during a final-approach briefing Thursday.
Both objects call the main asteroid belt home. The belt encircles the sun between the orbits of Mars and Jupiter.
Dawn is the first NASA mission designed to visit and orbit two objects with the same spacecraft.
As planetary scientists crafted their to-do list for a visit to Vesta, it became clear that "this tiny world has huge importance," says Carol Raymond, the mission's deputy lead scientist and a researcher at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Vesta is a window into the early origins of our solar system and the terrestrial planets."
In some ways, the notion of looking at asteroids and their tailed cousins, comets, as "windows on the early solar system" has become something of a cliché – an early hope that has been fulfilled in some cases, but not in others, as researchers have learned that some of these objects have been heavily altered by their billions of years orbiting the sun.