Rosetta Discovers Haunting Beauty in Deep Space

July 14, 2010: The European Space Agency's Rosetta spacecraft has beamed back close-up photographs of asteroid Lutetia, an ancient, cratered relic from the dawn of the solar system. Scientists are abuzz about the stunning images, which reveal a worldlet of haunting, alien beauty.

"I've never seen anything like it," says Claudia Alexander, project scientist for the U.S. Rosetta Project. "It looked as though it could have been fractured off of a mother asteroid – it was all angles and flat planes, ancient impacts overlaid by newer ones, covered by dust of some kind."

She is particularly intrigued by a giant dent in the asteroid's side.

"My first guess would be that it's the remnant of a giant collision that occurred sometime in the distant past," says Alexander. "The edges look shallow rather than sharp and deep as might be the case with a fresh crater. I'm sure there will be much more analysis of that feature in the weeks to come."

And then there's the perplexing appearance that boulders rolled down Lutetian slopes at some point.

"If that is indeed what we're seeing, the question becomes 'what could have caused the rolling? Perhaps the asteroid spun-up, spun-down, or experienced some orbital irregularity. It's not clear right now that the asteroid is subject to the forces that could cause these things. This is another issue for further study."

"Right now we have more questions than answers," Alexander continues. "We can only speculate at this point about what we're seeing in the pictures."

Asteroid Lutetia has been a target of interest among astronomers for many years. It is one of the largest asteroids in the solar system and has a strange spectrum of reflected light that doesn't look quite like any other asteroid. When the opportunity presented itself for Rosetta to pay a visit en route to its prime target, comet 67P/Churyumov-Gerasimenko in 2014, mission planners couldn't pass it up.

Now that Alexander has seen the images, she can't help but wonder what it would be like to have a walk around.

"Astronauts would have a hard time walking on Lutetia -- the gravity is likely to be much less than that of the moon," she says. "Also, the surface regolith looks very powdery, so astronauts might find themselves sinking in maybe a half-inch or so as they walked."

NASA's MIRO (Microwave Instrument for the Rosetta Orbiter) instrument will help determine whether the surface layers are powdery or rocky. As scientists analyze data from Rosetta's other instruments, they'll be able to determine Lutetia's mass and density, thus revealing more about the asteroid's composition and helping solve the riddle of its origin.

Is Lutetia a 130-km fragment from a planet that broke apart billions of years ago? Or is it one of the original planetary building blocks astronomers call "planetesimals" that has remained the same because no planet sucked it in during the solar system's formative years?

As scientists begin to answer these questions with the Rosetta data, they'll gain new insights into the origin and history of asteroids, and also learn more about the evolution of the solar system itself. An asteroid's contents can reveal something about the conditions and makeup of the solar nebula where the asteroid formed.

"Rosetta took measurements with 17 different instruments," says Rita Schulz, ESA Project Scientist for the Rosetta Mission. "When all the data are analyzed, Lutetia will be one of the best known asteroids out there."

"These spectacular images," she says, "are just the beginning."