Once in the coma and ionized, these molecules are strongly influenced by the electrical properties of the solar wind. As the solar wind becomes more intense as the comet approaches the sun, these ions "feel" a greater acceleration by the solar wind, are ejected from the coma and lost to space. Some of these ions also crash back down onto the surface of the nucleus.
In addition, particles slamming into the nucleus directly from the solar wind can have a "sputtering" effect, blasting material directly from the nucleus and sweeping it away into the comet's tail. These particles leave a spectroscopic fingerprint in the comet's tail, a signal that can be measured by Rosetta.
Rosetta's Double Focussing Mass Spectrometer (DFMS) instrument has detected these sputtered atoms, revealing a multitude of elements present in 67P's ion tail. According to a Rosetta blog update, these elements include sodium, potassium, silicon and calcium. Interestingly, all these elements are also present in a rare class of meteorite called carbonaceous chondrites. However, there are different abundances in the comet than the meteorites, so some work needs to be done to explain the variation.
ANALYSIS: Rosetta's Comet Fires its Jets
Mission scientists are expecting the sputtering rate to decrease as 67P gets closer to the sun. As the comet heats up, more gases are ejected from the nucleus, thickening the coma. This can have a deflection effect on solar wind particles, preventing them from getting close to the nucleus.
This deflection is already taking place, as observed by the spacecraft's Rosetta Plasma Consortium Ion and Electron Sensor. The instrument has found that solar wind ions have been deflected by as much as 45 degrees away from the comet and then this deflection is greatest for lighter solar wind ions such as protons.
This latest release of Rosetta findings have, for the first time, detailed the complex interplay between comet and solar environment and, as 67P reaches perihelion in mid-August, the mission will have given us a very privileged look at the evolution of a comet's coma and tail throughout a close solar encounter.
Source: ESA Rosetta blog