Electron rain and aurora generation on the surface of Mercury

A careful analysis of observations made by the BepiColombo space probe as it flew past Mercury on October 1, 2021 has revealed how electrons raining down on that planet’s surface can trigger high-energy auroras on that surface.

The study was carried out by the international team of Sae Aizawa, from the Institute for Research in Astrophysics and Planetology (IRAP) in France, who is now at the Institute for Astronautical and Space Science (ISAS) of JAXA (the Japanese space agency). .

BepiColombo is the result of a collaboration between JAXA and the European Space Agency (ESA). The BepiColombo space probe actually consists of two coupled spacecraft, ESA’s MPO (Mercury Planetary Orbiter) and JAXA’s Mio (formerly MMO for Mercury Magnetospheric Orbiter). Both spacecraft will undock for independent research flights in the last phase of their mission.

Terrestrial auroras are generated by interactions between the solar wind (a stream of charged particles emitted by the Sun) and an electrically charged upper layer of Earth’s atmosphere, called the ionosphere. Since Mercury only has a very thin atmosphere, classifiable as an exosphere, its auroras are generated by the direct interaction of the solar wind with the planet’s surface.

During its first flyby of Mercury, BepiColombo came as close as 200 kilometers from the planet’s surface. The observations made by the instruments on board Mio allowed for the first time to simultaneously observe different types of charged particles coming from the solar wind in the vicinity of Mercury.

Artist’s impression of the BepiColombo spacecraft flying over Mercury through a shower of electrons that hits its surface and can generate X-ray auroras on it. (Image: Thibaut Roger / Europlanet. CC BY SA)

For the first time, it was possible to observe how electrons are accelerated in Mercury’s magnetosphere and rush onto the planet’s surface. Although Mercury’s magnetosphere is much smaller than Earth’s and has a different structure and dynamics, the authors of the new study have confirmed that the aurora-generating mechanism is the same on Earth as it is on Mercury, as surely as well. it is in all the other stars of our solar system.

The study is titled “Direct evidence of substorm-related impulsive injections of electrons at Mercury”. And it has been published in the academic journal Nature Communications. (Fountain: NCYT by Amazings)