NASA 'exhilarated' as Dawn orbits mini-planet Ceres

NASA engineers said Friday they are "exhilarated" by the final maneuver in a 7 1/2 year "celestial dance" that put the spacecraft Dawn into orbit around the mini-planet Ceres 310 million miles from Earth.

At 7:39 a.m., EST, as the spacecraft, trailing a beam of blue-green vapor, closed in on the dwarf planet, Ceres "reached out and tenderly took the newcomer from Earth into its permanent gravitational embrace," said Marc Rayman, Dawn's chief engineer and mission director at NASA's Jet Propulsion Laboratory in Pasadena, Calif., in his Dawn Blog.

"This beautifully choreographed celestial dance is now a pas de deux," he said.

From its launch in September, 2007, Dawn has traveled 3.1 billion miles to reach Ceres in the asteroid belt between Mars and Jupiter.

"We feel exhilarated," said Chris Russell, principal investigator of the mission at UCLA. "We have much to do over the next year and a half, but we are now on station with ample reserves, and a robust plan to obtain our science objectives."

Jim Green, the director of NASA's Planetary Science Division, said Dawn's mission "allows us to look back in time to see how terrestrial planets are put together."

The crucial radio signal that arrived at JPL at 8:36 a.m. EST confirmed that Dawn was healthy and thrusting with its ion engine, the indicator it had entered orbit as planned.

"Since its discovery in 1801, Ceres was known as a planet, then an asteroid and later a dwarf planet," said Rayman. "Now, after a journey of 3.1 billion miles and 7.5 years, Dawn calls Ceres, home."

Dawn offered it's own assessment via Twitter: "Confirmed: I am in orbit around #Ceres."

The spacecraft then almost immediately swung behind the the dark side of the mini-planet and won't be able to deliver images until April.

Its first science orbit will take place April 23 with an altitude of 8,400 miles above Ceres. Its final orbit will take it 230 miles above the surface.

Dawn's job is to tell all about Ceres, which was discovered more than 200 years ago but has let slip very little about itself. Does it have polar ice caps? Does it have a liquid ocean? And could it have once harbored – or could it still harbor -- life?

The planet has been like "your secretive neighbor. Ceres would tell us nothing," said Russell. "Everything we're seeing was unexpected."

Among the most unexpected sights are the two astonishingly bright spots nestled in a crater on Ceres's surface. Photographed by Dawn's camera Feb. 19, the dots have the experts buzzing with speculation. Maybe a direct hit from an asteroid -- a space rock – excavated some buried ice. Maybe the bright spots are a sheen of minerals deposited by gushing geysers.

The spots "are unique in the solar system," Carol Raymond, deputy principal investigator of the Dawn mission said at a NASA briefing Monday. "The mystery will be solved, but it's really got us at the edge of our seats."

Like the big boys of the solar system, Ceres first took shape some 4-1/2 billion years ago from gas and dust. Unlike the true planets, Ceres froze in a state of arrested development, never growing beyond roughly a third the size of our moon.

Ceres "made it to the last rank before planet," says planetary scientist Andy Rivkin of the Johns Hopkins University Applied Physics Laboratory, who has studied the body. "The planets formed out of things that were Ceres-sized." Ceres, he says, can teach us what it takes to build an object such as the icy moons adorning some of the solar system's bigger planets.

Though it's not a full-fledged planet, Ceres does merit the consolation title of "dwarf planet," a title awarded to round bodies that, though big, are too small to make everything else get out of their way. Ceres is one of only known five dwarf planets – Pluto is another – and the first to host an orbiting spacecraft.

Scientists know that Ceres once had an icy ocean at its core and probably still does. But it's also possible that radioactivity inside the planet melted some of the ice, creating a lake or a sea. Dawn will look for a liquid ocean.

If it's there, says Dawn science team member Mark Sykes, director of the Planetary Science Institute in Tucson, that "raises the question, if water equals life, could life have evolved under the surface of Ceres?" He and others agree that Ceres may once have been hospitable to life, though it may no longer be so.

Just because Ceres is intriguing doesn't mean it was easy to mount an expedition there. NASA canceled Dawn twice, recalls Russell, one of the mission's founders. One cancelation came on Christmas Eve; Russell learned about the second cancelation at his mother's funeral.

After finally launching in 2007, the $473-million Dawn made a successful trip to the space rock Vesta before heading to Ceres. But the sailing hasn't always been smooth. Two of the gyroscope-like devices that help point the craft in the right direction have failed. Radioactive particles zapped the ship, triggering a cascade of problems.

Inventive engineering got the spacecraft back on its feet, and it's now expected to collect even more data at Ceres than originally planned, Rayman says.

When it starts to orbit Ceres, Dawn will become the first spacecraft in history to orbit two extraterrestrial objects, a feat impossible without its high-tech propulsion system. Like the TIE fighters in "Star Wars," Dawn is powered by so-called ion engines, which rely on electrically charged atoms called ions to push the craft ahead. The engines are far more efficient than conventional rocket engines, allowing the spacecraft to cover some 3 billion miles on a very small amount of fuel.

Dawn will study Ceres until at least mid-2016. The official end of its mission has not yet been determined. One thing is clear, Raymond said: "Discoveries lie ahead."