Rosetta's journey with a comet has already revealed a dark world far more complex than scientists had realized.
In a flurry of papers published Thursday in the journal Science, researchers provide the first data-driven snapshot of comet 67P/Churyumov-Gerasimenko — a world of towering cliffs, wide basins, powdery surfaces blacker than coal, and a growing atmosphere that will soon be strong enough to deflect the solar wind.
A few other spacecraft have flown past comets, but Rosetta is the first to travel alongside one as it makes its way to perihelion, the moment when it is closest to the sun. Comet 67P will reach that milestone in the middle of August.
When the suite of instruments aboard Rosetta first started taking measurements of 67P, the dumbbell-shaped comet was more than 325 million miles from the sun. At that distance, on the other side of the asteroid belt, it was too faint to see from ground-based telescopes.
“We don't have a lot of previous observations of comets in that part of the solar system," Weissman said. “We are exploring unknown territory.”
Most of the findings reported in Science are based on data collected between April and September, when Rosetta was still sailing toward 67P, and months before a lander carried by Rosetta, known as Philae, maneuvered to a nail-biting arrival upon the comet’s surface.
Each of the seven Science papers describes a different aspect of the comet, including observations of the size and density of the dust in its coma and the composition of the organic material on its surface.
One of the papers reveals that jets of gas streaming off the comet are coming primarily from the “neck” region.
In another report, researchers identified 19 distinct geographical areas on 67P that have been named for Egyptian deities, including Ma'at, Imhotep, Aten and Ash.
At two locations, scientists found terrain covered in about 3 to 15 feet of dust. In another region, they found fractures in the comet's surface and circular depressions with steep walls.
The head of the nucleus sports a large, shallow, circular depression that is more than half a mile across.
Scattered around the nucleus is a system of what scientists call pits — quasi-circular depressions that measure 150 to 1,000 feet in diameter and 30 to 700 feet deep. Scientists believe they see fine jets of gas rising up from these pits.
On the steep slopes of the nucleus, small bumps 9 feet in diameter were spotted. Such features have never been seen on a comet, and the scientists dubbed them “goose bumps.” These boulders may be the building blocks of the comet, Weissman said.
“The images of the goose-bump terrain in the pits are suggesting that the nucleus is indeed a rubble pile, but all the rubble is about the same size,” he said. “This is consistent with current ideas about how accretion of comets worked in the early solar system.”
So far, scientists have found no evidence of water on 67P’s surface, suggesting its remaining water is insulated from the sun's warmth by its dusty coat.
“These papers represent our first look at what the comet has to offer,” said project scientist Matt Taylor of the European Space Agency. “The results also set a base line for continuing observations as ... the comet gets closer to the sun.”
Rosetta is still in the early phase of its data collection, and 67P will continue to evolve over time. Just a few months from now, its characteristics may be completely different.
Still, even at this early stage, the detailed study of a single comet can help scientists better understand the comets seen through telescopes on Earth.
“Anything that we get from Rosetta sets us up for a much broader understanding of comets in general,” Taylor said.