Auroras – the solar system's universal light show (except Neptune... sorry, Neptune)

Scientists have found that the fundamental mechanism behind the spectacular light shows of auroras on Earth are universal throughout the solar system.

Using data from space probe BepiColombo's first flyby of Mercury, the researchers have shown the processes creating auroras on the planet closest to the Sun are shared with those scientists understand on Earth.

Although earlier observations had shown Mercury's magnetosphere interacts with solar wind similarly to that on Earth, the processes are much faster and experimental evidence for the roles of electrons during this cycle was missing.

Auroras, like the aurora borealis seen in Earth's northern hemisphere, are caused by solar winds of charged particles, steered by a planet's magnetic field, colliding with gases in the atmosphere.

Launched on an Ariane rocket in 2018, BepiColombo took a seven-year trip around the solar system, dropping by Mercury on the way, where it measured the magnetic field, magnetosphere, and both interior and surface structure.

A team led by Sae Aizawa, a post-doctoral researcher at France's Research Institute in Astrophysics and Planetology, have analyzed measurements of low-energy electrons of less than 30 kiloelectron volts and ions during the BepiColombo mission's first flyby of Mercury in October 2021.

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The results show evidence that energetic electrons are accelerated in Mercury's magnetosphere and are later injected onto closed magnetic field lines on the planetary nightside.

In a paper published in Nature Communications this week, researchers said that, despite differences in the structure and dynamics of the planetary magnetospheres, processes involved in producing auroras are similar throughout the solar system.

"The BepiColombo observations further reveal that electron magnetospheric injections and subsequent energy dependent drift are remarkably similar to that at Earth despite the smaller scale of the magnetosphere of Mercury which is more sensitive to the external solar wind," the study said.

"Electron injections are therefore a universal mechanism in our solar system that generates different types of aurora now observed at all magnetized planets, except Neptune, as well as above Martian crustal magnetic fields, despite the differences in structure and dynamics of their magnetospheres."

Those thinking of buying a ticket for a round trip to Mercury – should one ever be available – to take in the phenomenon shouldn't bother, though. The observations made so far are in the X-ray band of the electromagnetic spectrum and would be invisible to the human eye. ®