The European Space Agency’s Rosetta mission made history when it delivered the Philae lander to the surface of comet 67P last month. The landing didn’t go perfectly to plan, but a great deal of science was still done by Philae. With all that going on, it can be easy to forget there’s still the Rosetta probe in orbit of the comet, and it has its own science to do.
The ESA has released some findings from Rosetta, and it can help scientists understand the formation of our home planet. According to this data, Earth’s water probably didn’t come from comets like 67P as many had thought.
Scientists have been researching as to why there’s so much water on Earth for some time. Based on understanding of planetary formation, the early Earth would have been so hot that any water native to it would have boiled off. Comets are essentially giant dusty snowballs, so they were a prime suspect as a water delivery mechanism.
Comets like 67P are in the Jupiter-family, meaning they currently have orbits governed by Jupiter, but are thought to have originated out in the Kuiper Belt beyond Neptune. The Jupiter-family comets seemed like a good match for Earth. They would have been in the right region of space and the first few that were measured had a D/H ratio in the right range. However, 67P does not.
The level of deuterium is even higher in 67P than in the long-period comets that have been measured. This indicates that Jupiter-family comets have too wide a variance in water makeup to be responsible for delivering most of Earth’s water. Comets surely played a small role, but almost every comet measured to this point has very high deuterium.
The first true color image of Comet 67P looks like Mars
