Rosetta satellite data gives most detailed view of comets yet

Research based on Comet 67P mission published in Science journal

The long-standing “dirty snowball” description of a comet can now be updated - a bit more of the dirty and a lot less of the snow.

Already outstandingly successful, the Rosetta satellite mission to visit and study Comet 67P/Churyumov-Gerasimenko continues to surprise as scientists peel back the layers on this ancient cosmic lump.

No fewer than seven research papers using Rosetta data are published this evening in the journal Science, giving us the most detailed view of a comet yet produced.

The satellite bristles with experiments and cameras and spectrographs that are revealing new things every day, and inform new research. For example, Holger Sierks and his colleagues tell us about the comet’s nucleus, which seems to be made of dust, rock and frozen gas. They suggest solid is the wrong word and its centre could be porous and fluffy.

Nicolas Thomas and colleagues used the Osiris infrared imaging system to examine the comet’s surface in another paper. They found that it has dunes and ripples and active dust transport that carves and shapes it like sand in a desert.

This seems to be in keeping with discoveries by Fabrizio Capaccioni and colleagues using Virtis, a thermal imaging spectrometer that shows the surface is generally dehydrated. There are plenty of opaque organic compounds but very little water ice.

Samuel Gulkis and colleagues used the Miro microwave instrument to show the internal temperature of the comet could change in daily and seasonal patterns. They found water ice is lost through sublimation, changing directly from a solid to a gas with most of the loss from the narrow “neck” of the comet.

Comet tail

Comets are famous for the cloud of dust and gas that surrounds the nucleus and trails off behind as a tail. Myrtha Hässig and colleagues have analysed what is in this dust envelope, or “coma”, and watched the movement of water as a gas, as carbon monoxide and carbon dioxide, in the dust.

As if chasing and catching up with a comet wasn't enough of an accomplishment, the mission was also famous because of the comet lander Philae. It landed, sending back important data as it touched down, but it then bounced and ended up in the shade of a cliff.

It shut itself down, but hopes remain high that its solar panels will get more light as the comet approaches the sun, so the lander may yet have a further part to play in the mission.

Dick Ahlstrom

Dick Ahlstrom

Dick Ahlstrom, a contributor to The Irish Times, is the newspaper's former Science Editor.