The European Space Agency (ESA) reports that on July 29 the Rosetta spacecraft observed the brightest and largest eruption from Comet 67P/Churyumov–Gerasimenko to date. Several of the spacecraft’s instruments took measurements from a distance of 116 miles (186 km) and the results were very interesting. The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) detected double the amount of carbon dioxide, quadruple the methane, and seven times the hydrogen sulfide detected just a couple of days before, while the amount of water stayed almost the same. The Rosetta Plasma Consortium’s magnetometer (RPC-MAG) detected a steep decrease in magnetic field strength close to the same time period in which the eruptive jet was observed visually by Rosetta’s Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS).
Mission scientists were still trying to determine if the jet originated from below the comet’s surface and the origin of the chemicals detected in the jet. But they explained the drop in magnetic field strength as being the result of gases and dust in the jet pushing the solar wind out away from the comet, at least to a distance of 116 miles (186 km). For a comet that is still considered by many to be a dirty snowball, or a snowy dirtball, these are indeed very interesting results.
Full press release:
ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA