3,200 Miles Over Ceres

A JPL composite video simulates a flyover of a dwarf planet.

The surface of Ceres as seen from Dawn, flying at 2,700 miles above the surface. Taken June 6, 2015. (NASA)
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As you read this, Dawn—the first spacecraft ever to observe two separate extraterrestrial bodies in a single mission—is about halfway through the 22-day “science survey” phase of what is intended to be a 16-month study of the dwarf planet Ceres, the largest body in the asteroid belt. It’s currently observing Ceres from an altitude of 2,700 miles.

That’s about one-third the distance from the surface that the probe was flying last week when it completed its first mapping orbit. Spacecraft controllers at the Jet Propulsion Laboratory in Pasadena, California combined images taken during that orbit with navigational imagery taken from an altitude of 3,200 miles to produce this flyover video. They also doubled the vertical relief and added a star field to the background.

The bright spots on the 600-mile-wide world’s surface remain mysterious. No evidence yet uncovered would controvert investigators’ best guess that they are highly reflective patches of ice or salt.

Dawn is currently orbiting Ceres every three days. In August, it will spiral down into a high-altitude mapping orbit about 920 miles above the surface, using its high-res camera and visible and infrared mapping spectrometer (VIR) to take near-global images. An even lower mapping orbit will follow in November, when the spacecraft will spiral down to just 230 miles from the surface, the better to measure Ceres’ gravity.

Investigators hope to learn more about the planet’s history by “reading the bumps—the phrenology of Ceres,” jokes Carol Raymond, a JPL investigator who heads up the lab’s Small Bodies office—where she keeps a plate-sized, 3D model of the southern hemisphere of Vesta, Dawn’s previous object of study before Ceres.

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