AIR & SPACE MAGAZINE

Dawn Spacecraft Closes in on Ceres

Soon we’ll find out what those mysterious bright spots are.

March 3, 2015

Dawn returned this image of Ceres on February 19, showing two bright spots in the center of a crater. One is twice as bright as the other. But what are they?

Scientists are eagerly looking forward to the arrival of NASA’s Dawn spacecraft at the dwarf planet Ceres this Friday, after more than seven years of traveling. They’re particularly anxious to see close-ups of mysterious bright spots that appear in one of the 600-mile-wide world’s large craters.

But they’ll have to wait another few weeks for those.

Dawn is now on the dark side of Ceres, as its ion-drive engines get ready to maneuver the spacecraft into orbit around the planet. The animation beginning at the 1:17 mark in the video below shows the approach into orbit.

Spacecraft controllers at NASA’s Jet Propulsion Laboratory in California won’t be in touch with Dawn when it enters Ceres orbit at 4:20 a.m. Pacific time on Friday. They’ll get the first confirming signal later that day, but no pictures. Dawn won’t start taking images again until it reaches the first of four successively lower “science orbits” in late April.

That’s when scientists will settle in for a 16-month investigation of Ceres, which has become much more interesting in recent weeks, after Dawn’s cameras revealed two bright spots in a 57-mile-wide crater. “These spots were extremely surprising” to the Dawn scientists, said deputy principal investigator Carol Raymond in a press conference yesterday. “The team is really, really excited about this feature because it is unique in the solar system.”

The high reflectivity suggests that it may be an ice deposit on the surface. But if it were the result of ice volcanoes, there should be a corresponding mound at the same location, and no such topographic feature appears. So it’s a mystery. And we may learn the answer even before Dawn reaches its lowest mapping orbit. By then the onboard camera should be able to map the surface with a resolution of just 115 feet, compared to the 2.2-mile resolution of the approach photo above.