Credit: European Space Agency

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 CH 4 , CO, CO 2 , CH 3 OH, CH 2 O, and H 2 O, for instance—that then reacted under the influence of cosmic rays or ultraviolet radiation.

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