After 8 years, Dawn probe brings Ceres into closest focus

Data coming back from dwarf planet Ceres could unlock secrets of the earliest days of our solar system, from Dawn’s mission director and chief engineer.

By Marc D Rayman, NASA

More than a thousand times farther from Earth than the moon, farther even than the sun, an extraordinary extraterrestrial expedition is taking place. NASA’s Dawn spacecraft is exploring dwarf planet Ceres, which orbits the sun between Mars and Jupiter. The probe has just reached the closest point it ever will, and is now beginning to collect its most detailed pictures and other measurements on this distant orb.

Ceres is a remnant from the dawn of our solar system nearly 4.6 billion years ago. All the data Dawn is now sending back will provide insight into Ceres’ history and geology, including the presence of water, past or present. Scientists believe that by studying Ceres, we can unlock some of the secrets of the epoch in which planets, including our own, formed.

Named for the Roman goddess of agriculture and grain, Ceres was the first dwarf planet discovered, in 1801. That’s 129 years before Pluto – and in fact, both were originally considered planets, only later to be designated dwarf planets.

The ion engines use xenon gas, a chemical cousin of helium and neon. With electrical power from Dawn’s large solar panels, the xenon is given an electrical charge in a process called ionization. The engines use high voltage to accelerate the ions. They’re then shot out of the engines at up to 90,000 mph. When the ions leave the spacecraft at this fantastically high speed, it’s pushed in the opposite direction. Dawn’s ion propulsion system is exceptionally efficient – 10 times as efficient as conventional spacecraft propulsion. It’s comparable to your car getting 250 miles per gallon.

We see rugged terrain and smooth areas, sometimes with streaks of material that’s flowed across it. There are craters large and small, created by billions of years of assaults in the rough-and-tumble neighborhood of the asteroid belt. We see mountains and valleys, huge fissures in the ground and bright spots that glow with a mysterious luster, reflecting much more sunlight than most of the dark surface.

The most striking of these shining regions, inside the 55-mile-wide Occator Crater (named for the Roman deity of harrowing), is so bright that the Hubble Space Telescope detected a hint of it a decade ago. [link to earthsky.org (secure)]