Odd comet is result of early merger in solar system
ESA/Rosetta/NAV/CAM/Creative Commons

Odd comet is result of early merger in solar system

The oddly shaped comet known as 67P/Churyumov-Gerasimenko is actually made of two separate ice orbs that collided and fused soon after the solar system formed, new images suggest. Those pictures, some of which are sharp enough to spot features 10 centimeters across, were taken by the European Space Agency’s Rosetta probe, which has been orbiting the comet (seen here in July from a distance of about 160 kilometers) for more than a year now. Each of 67P’s lobes has a series of ridges and terraces stretching across its surface. These distinct, sharp-edged features—somewhat akin to bathtub rings—suggest that each of the comet’s lumps has an outer shell of onionlike layers that is at least several hundred meters deep, the researchers report online today in Nature. But the narrow neck connecting the two lobes has no such features—a sign that the comet didn’t start out as one round, layered object that then gained an unusual shape by spewing material unevenly. Instead, the researchers propose, each lobe formed separately and then merged via a collision so gentle that each ice ball’s layered structure was preserved. The cosmic fender bender may have happened less than 100 million years after the solar system formed. Since that time, material vaporizing from sunlit areas of the comet and then condensing in shadowed regions (which a recent report suggests are about 50°C cooler than those illuminated by the sun) may have helped form the neck joining the once-separate objects.