BepiColombo, the joint European Space Agency (ESA) and Japanese Aerospace Exploration Agency (JAXA) mission, revealed how a shower of electrons on the surface of Mercury can trigger auroras with high energy .
The mission, which has been heading to the innermost planet of the solar system since 2018, successfully conducted its first Mercury flyby on October 1, 2021. An international team of researchers analyzed data from three of the instruments in BepiColombo during the encounter. The results of this study were published in Communication in Nature.
Terrestrial auroras are created 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. As Mercury has only a thin atmosphere, called the exosphere, its auroras are generated by the solar wind interacting directly with the planet’s surface.
The BepiColombo mission consists of two spacecraft, the Mercury Planetary Orbiter (MPO) led by ESA, and the Mercury Magnetospheric Orbiter (MMO, named Mio after launch) led by JAXA, which are currently in a docked configuration for seven-year cruise to the final orbit. During its first Mercury flyby, Bepicolombo flew 200 kilometers above the surface of the planet. Observations by the plasma instruments aboard Mio enabled the first simultaneous observations of different types of charged particles from the solar wind around Mercury.
Lead author, Sae Aizawa, of the Institut de Recherche en Astrophysique et Planétologie (IRAP), now at JAXA’s Institute of Space and Astronautical Science (ISAS) and the University of Pisa, Italy, said, “For the first time, we witnessed when how The electrons are accelerated in the magnetosphere of Mercury and penetrate the surface of the planet. While the magnetosphere of Mercury is smaller than the Earth and has a different structure and dynamics, we have confirmation that the mechanism that produces aurorae is the same throughout the solar system. ”
During the flyby, BepiColombo approached Mercury from the night side of the northern hemisphere and made its closest approach to the morning side of the southern hemisphere. It observes the magnetosphere in the sun’s southern hemisphere, and then passes from the magnetosphere back into the solar wind. Its instruments have successfully observed the structure and boundaries of the magnetosphere, including the magnetopause and bow shock. The data also show that the magnetosphere is in an unusually compressed state, possibly due to the high pressure conditions of the solar wind.
The acceleration of electrons appears to occur due to plasma processes in the dawn part of Mercury’s magnetosphere. High-energy electrons are carried from the tail region toward the planet, where they eventually rain down on Mercury’s surface. Unhindered by the atmosphere, they interact with surface material and cause X-rays to be emitted, resulting in an auroral glow. Although auroras have previously been observed on Mercury by the NASA MESSENGER mission, the processes that cause surface X-ray fluorescence have not been well understood and witnessed directly until now.
Sae Aizawa, Direct evidence of substorm-related impulsive injection of electrons in Mercury, Communication in Nature (2023). DOI: 10.1038/s41467-023-39565-4. www.nature.com/articles/s41467-023-39565-4
Citation: First BepiColombo flyby of Mercury finds electron rain causing X-ray auroras (2023, July 18) retrieved on July 18, 2023 from https://phys.org/news/2023-07-bepicolombo-flyby-mercury- electron-triggers.html
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