If you have an ACS member number, please enter it here so we can link this account to your membership. (optional)

ACS values your privacy. By submitting your information, you are gaining access to C&EN and subscribing to our weekly newsletter. We use the information you provide to make your reading experience better, and we will never sell your data to third party members.


Physical Chemistry

Rosetta Reveals Details About Comet 67P/Churyumov-Gerasimenko

Space: Initial data shows the comet is covered with a polymeric, organic material

by Jyllian Kemsley
January 22, 2015 | A version of this story appeared in Volume 93, Issue 4

An image of the 67P/Churyumov-Gerasimenko comet taken from Rosetta with an artist’s impression of the Rosetta orbiter.
Credit: European Space Agency
Rosetta, shown in an artist’s rendering, is studying comet 67P, which is about 4 km in diameter.

The comet known as 67P/Churyumov-Gerasimenko has a morphologically complex, organic-rich surface, according to analysis of the first set of data from the Rosetta mission (Science 2015, DOI: 10.1126/science.aaa4542).

Comets are the fossils of our solar system, says Carey M. Lisse, a principal scientist at the Johns Hopkins University Applied Physics Laboratory. Their interiors contain pristine material remaining from when a giant molecular cloud collapsed into both the sun and a protoplanetary disk. The disk material gathered into planets, moons, asteroids, and comets.

Unlike prior “fly by” missions to study comets, the European Space Agency’s Rosetta is now orbiting 67P. It will continue to study the characteristics and chemistry of the comet’s atmosphere, surface, and nucleus throughout this year as 67P passes through the part of its orbit that brings it closest to the sun.

“It’s a huge leap compared to what we’ve done in the past,” says Donald E. Brownlee, a professor of astronomy at the University of Washington.

The first data from Rosetta, collected in August and September 2014, show that in some ways the comet is more heterogeneous than expected. Researchers studying its surface morphology have identified five categories of terrain, including “pitted” and “smooth.”

Spectroscopy of the comet’s surface, on the other hand, shows that the chemical composition is largely the same across the comet’s different surfaces, possibly the result of dust getting distributed among terrains. 67P is covered in a stable, polymeric organic material with various carbon-hydrogen and oxygen-hydrogen groups, one analysis shows (Science 2015, DOI: 10.1126/science.aaa0628). Scientists believe the material arose from small molecules present when the comet formed—ices of CH4, CO, CO2, CH3OH, CH2O, and H2O, for instance—that then reacted under the influence of cosmic rays or ultraviolet radiation.

Rosetta scientists hope in time to extract more chemical details from the data, says the spectrometer’s lead scientist, Fabrizio Capaccioni, a senior researcher at Italy’s National Institute for Astrophysics. “These are just the first two months of studies,” he notes. “We’re using lab measurements and detailed analyses of the surface to improve our understanding.”



This article has been sent to the following recipient:

Chemistry matters. Join us to get the news you need.