Data from the BepiColombo space probe have confirmed the mechanism of polar lights on the closest planet to the Sun. The reclosure of Mercury's magnetic field lines directs streams of charged particles directly to its surface. Colliding with local minerals, they cause flares in the X-ray range.
Mercury's global magnetic field is a hundred times weaker than Earth's. However, from time to time it releases large amounts of energy that accelerate streams of solar particles and send them towards the planet. In the absence of an atmosphere, they collide with the surface at high speed, causing auroras in the invisible X-ray range. Such a mechanism has been described thanks to observations by the BepiColombo spacecraft. It is described in a new article published in the journal Nature Communications.
Our star is constantly watering the neighborhood with streams of charged particles. The first under it falls Mercury, whose magnetic field is noticeably deformed under the pressure of this solar wind. As a result, on the side oriented to the Sun, it is "squeezed in", and on the opposite side is stretched "tail". Gradually, this plume becomes longer and longer, the magnetic field force lines in it cross and re-lock. Some of them go directly to the surface of Mercury, and on them rush streams of solar wind - primarily electrons.
On Earth and many other bodies in the solar system, this process causes solar particles to collide with molecules in the atmosphere, ejecting excess energy in the optical range of the spectrum. The result is bright auroras. On Mercury, there is virtually no atmosphere, and electrons travel straight to the planet's surface. Here they collide with rocky rocks, creating flashes of high-energy X-rays.
Such auroras were first observed by the MESSENGER space probe orbiting Mercury between 2011 and 2015. However, it had no instruments that could track the charged particles and confirm the mechanism of the flares. So now scientists have used the data that the BepiColombo spacecraft collected during its approach to Mercury in 2021. Flying through its magnetosphere, the probe recorded streams of electrons streaming toward the surface. This confirms the mechanism that has been proposed to explain the planet's X-ray auroras.