As NASA’s Dawn spacecraft makes its final approach to Ceres, the ion-propelled spacecraft is sending the best images yet with more details about the surface of the dwarf planet. The images from Dawn have shown the presence of numerous craters and unusual bright spots that scientist hope will provide clues as to not only how Ceres formed and if it is still active, but the early history of the Solar System as well.
Dawn's ions thrusters don't have much more pressure than the weight of a sheet of paper, so the spacecraft's arrival on Friday will be a gradual one. It will go into a high orbit around Ceres and then slowly spiral in. First it will orbit at an altitude of 8,400 miles (13,500 km) and then as the mission progresses it will move down to its survey orbit of 2,700 miles (4,400 km). It will then spiral into its High Altitude Mapping Orbit (HAMO) of 910 miles (1,470 km), which will take six weeks. At the end of the year it will move to its Low Altitude Mapping Orbit (LAMO) of 230 miles (375 km), where it will remain for the rest of the mission.
Discovered in 1801 by Sicilian astronomer Father Giuseppe Piazzi and named after the Roman goddess of agriculture and fertility, Ceres remained little more than a spot of light. Even the Hubble Space Telescope could capture only a featureless blur. Now the unmanned probe is revealing craters and other features that will be named after gods and goddesses of agriculture and nature from mythology as well as harvest festivals.
Dawn was launched on September 27, 2007 atop a Delta II rocket from Space Launch Complex 17B at Cape Canaveral Air Force Station, Florida. After making a flyby of Mars on February 4, 2009 in a slingshot maneuver, it went into orbit around the protoplanet Vesta on July 16, 2011, where it carried out a 14-month survey of its surface.
The 1,240 kg (2,730 lb) spacecraft then used its ion thruster to send it on a three and a half year passage to Ceres. during which it has returned unsurpassed new high-resolution images of the body. When it arrives in orbit on March 6, it will mark the first visit to a dwarf planet by any spacecraft. By visiting Vesta and Ceres, Dawn will have visited the two most massive objects in the asteroid belt between Mars and Jupiter.