First BepiColombo flyby of Mercury finds electron rain triggers X-ray auroras

BepiColombo, the joint European Area Company (ESA) and Japanese Aerospace Exploration Company (JAXA) mission, has revealed how electrons raining down onto the floor of Mercury can set off high-energy auroras.

The mission, which has been enroute to the solar system’s innermost planet since 2018, efficiently carried out its first Mercury flyby on October 1, 2021. A world workforce of researchers analyzed information from three of BepiColombo’s devices throughout the encounter. The outcomes of this examine have been revealed in Nature Communications.

Terrestrial auroras are generated by interactions between the solar wind, a stream of charged particles emitted by the sun, and an electrically charged higher layer of Earth’s environment, known as the ionosphere. As Mercury solely has a really skinny environment, known as an exosphere, its auroras are generated by the solar wind interacting instantly with the planet’s floor.

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, that are at the moment in a docked configuration for the seven-year cruise to the ultimate orbit. Throughout its first Mercury flyby, Bepicolombo swooped simply 200 kilometers above the planet’s floor. The observations by plasma devices onboard Mio enabled the primary simultaneous observations of various sorts of charged particles from the solar wind within the neighborhood of Mercury.

Lead creator, Sae Aizawa, of the Institut de Recherche en Astrophysique et Planétologie (IRAP), now at JAXA’s Institute of Area and Astronautical Science (ISAS) and College of Pisa, Italy, stated, “For the primary time, now we have witnessed how electrons are accelerated in Mercury’s magnetosphere and precipitated onto the planet’s floor. Whereas Mercury’s magnetosphere is way smaller than Earth’s and has a special construction and dynamics, now we have affirmation that the mechanism that generates aurorae is identical all through the solar system.”

Through the flyby, BepiColombo approached Mercury from the evening facet of the northern hemisphere and made its closest approach close to the morning facet of the southern hemisphere. It noticed the magnetosphere on the daytime facet of the southern hemisphere, after which handed out of the magnetosphere again into the solar wind. Its devices efficiently noticed the construction and the boundaries of the magnetosphere, together with the magnetopause and bow shock. The information additionally confirmed that the magnetosphere was in an unusually compressed state, more than likely attributable to excessive strain circumstances within the solar wind.

The acceleration of electrons seems to happen attributable to plasma processes within the daybreak facet of Mercury’s magnetosphere. The excessive vitality electrons are transported from the tail area in the direction of the planet, the place they ultimately rain down on the Mercury’s floor. Unimpeded by an environment, they work together with materials on the floor and trigger X-rays to be emitted, leading to an auroral glow. Though auroras had been noticed earlier than at Mercury by the NASA MESSENGER mission, the processes triggering the X-ray fluorescence by the floor had not been nicely understood and witnessed on to date.