The early Rosetta results are in, and they reveal that comets are much more complicated than anyone knew.
In a flurry of seven papers published late last month in the journal Science, researchers provide the first data-driven snapshot of comet 67P/Churyumov-Gerasimenko — a world of towering cliffs, wide flat basins, powdery surfaces blacker than coal, and a growing atmosphere that will soon be strong enough to deflect the solar wind.
“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 baseline for continuing observations as we watch the nucleus and coma develop as the comet gets closer to the sun.”
A handful of other spacecraft have flown past comets, but Rosetta is the first one to travel alongside a comet as it makes its way to perihelion in August — the moment when it will be closest to the sun.
When the suite of instruments aboard Rosetta first started taking measurements of 67P, the comet was more than 3.5 astronomical units from the sun. (One astronomical unit is the distance between the sun and Earth). At that distance the comet was too faint to see from ground telescopes.
Most of the data referenced in the Science studies were collected between April and September, when Rosetta was still sailing toward the comet, and months before Philae’s nail-biting landing on its surface.
“What these papers are talking about is a place where we don’t have a lot of previous observations of comets,” said Paul Weissman of the Jet Propulsion Laboratory and an interdisciplinary scientist on the mission. “We are exploring unknown territory.”
Each of the Science papers describes a different aspect of the comet including observations of the size and density of the dust in its coma, the composition of the organic material on its surface, where the gas jets seem to spring from its nucleus, and its mesmerizing geology.
So far, scientists have found no evidence of water on the comet’s surface, suggesting that the comet’s remaining water is insulated from the sun’s warmth by the comet’s dusty coat. Another paper notes that jets of gas streaming off the comet are coming primarily from the neck region.
Researchers have also identified 19 distinct geographical areas that have been named for Egyptian deities like Ma’at, Imhotep, Aten and Ash.
At two locations scientists found terrains covered in up to 3 to 15 feet of dust. In another region they found fractures in the comet’s surface and circular depressions with steep walls. In still another region, on the head of the nucleus, there is a large shallow, circular depression that is more than half a mile in diameter.
Scattered around the nucleus, the scientists observed a system of what they call pits — quasi-circular depressions that are 150 to 1,000 feet in diameter and 30 to 700 feet in depth. There is evidence that there are some gas jets rising up from these pits.
On the steep slopes of the nucleus, they spotted a never before seen feature on a comet — small bumps 9 feet in diameter that have been given the colloquial name “goosebumps.”
Weissman said these similar-sized boulders may be the building blocks of the comet.
“The images of the goosebump 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.
“The picture is starting to come together, which is a very exciting result from the mission,” he added.
Rosetta is still in the early phase of its data collection, so these studies offer just one look at a body that will continue to evolve over time.
“Each paper provides us with our first idea of the comet and its characteristics, but we have the evolution of its activity to comprehend,” said Taylor.
