Water ice found on Rosetta’s comet sheds light on comet’s origins

Yes, there is water ice on Comet 67P/Churyumov-Gerasimenko, Observations conducted by the European Space Agency’s Rosetta spacecraft shortly after its arrival in 2014 have confirmed.

The ESA announced the finding Wednesday in a press release, explaining that while water vapor can be seen flowing from the comet, the vast majority of the ice appears to be beneath the comet’s crust. Precious few samples of exposed water ice have been detected on the surface.

As New Scientist explained, this doesn’t exactly come as a shock, as previous comet fly-bys had spotted microscopic grains of ice on the surface. The new research, published earlier this week in the journal Nature, used Rosetta’s infrared detector to find exposed ice grains on cliff faces.

That infrared detector, dubbed the VIRTIS instrument, analyzed the topmost layer of Comet 67P and found that it is coated primarily in a dark, dry, and organic-rich material, the ESA said. There is a tiny amount of H2O mixed into that material, however, the organization added.

Discovery sheds new light on the comet’s composition

Lead author Gianrico Filacchione of the National Institute for Astrophysics in Rome, Italy, and his colleagues reviewed observations conducted by the VIRTIS instrument between September and November 2014. They found two areas, tens of meters long, in the comet’s Imhotep region that appear as bright patches in visible light and contained significant amounts of water ice.

The pure water ice was found to make up approximately five percent of each pixel sampling area and had an average temperature of around -120 degrees Celsius when detected, the ESA said. By comparing these infrared measurements to models evaluating how various-sized ice grains could be mixed together in one pixel, they calculated the abundance of the frozen water.

They found two different types of grains: one that is several tens of micrometers in diameter, and another that is much larger (nearly two millimeters in size). The latter ones are much bigger than any that had been previously detected, New Scientist explained, which indicates they likely grew more slowly. The researchers believe the ice formed when the comet was far away from the sun.

Co-author Murthy Gudipati, a planetary scientist at the Jet Propulsion Laboratory, told the Los Angeles Times that the discovery was “exciting because now we are starting to understand the upper dynamic layers of the comet and how they evolved… We knew water ice made up the majority of the comet, but we didn’t know how deep or in what condition it was. This shows that it not very deep at all – perhaps just a few feet beneath the surface.”


Feature Image: ESA