Density Increases in the Cometary Plasma Environment and Their Relation to Magnetosheath Jets

In the cometary plasma environment, the solar wind interacts with the expanding coma of heavy cometary ions. At high gas production rates, it can have plasma environment characteristics similar to the environment of Mars, with a bow shock and a cometosheath. Magnetosheath jets are transient enhancements in the dynamic pressure of the magnetosheath plasma. They can be generated at a disturbed bow shock surface and have been confirmed at Mars, Earth, and possibly Jupiter and Mercury. We have adapted commonly used methods to find magnetosheath jets to the Rosetta data at 67P/Churyumov–Gerasimenko and find candidate events throughout the postperihelion mission. We show that the identified density enhancements have similarities to magnetosheath jets. The events are of typical duration and density enhancement, and occur at a time when the bow shock is thought to be close to the spacecraft. We found a cometary ion velocity enhancement, although no conclusion on the solar wind velocity can be reached due to lack of data. These jet-like features are embedded in the heavy-ion population. We hypothesize that jets are formed in the solar wind ion population in the cometosheath, and then, as the two plasmas interact, are transferred to the cometary ion population. While we cannot rule out other phenomena that could cause these jet-like enhancements, they bear a remarkable resemblance to magnetosheath jets at Mars and Earth. If they are indeed jets, then this is the first time jets have been shown to exist in a plasma environment dominated by heavy ions.