Mercury discovered to have aurora, surprising scientists

Michelle Starr
Science Alert
Wed, 19 Jul 2023 11:16 UTC

© Griffith Observatory

An illustration of the surface of Mercury.

A probe sent to study the sadly neglected innermost planet of the Solar System has finally revealed auroral processes that take place in spite of a practically nonexistent atmosphere.

In October 2021, the BepiColombo probe took measurements of electrons and ions at Mercury, finding evidence of their acceleration. Analysis showed that this was the result of auroral processes involving Mercury's magnetic field, ultimately producing a faint X-ray emission.

This means aurorae have now been seen on every single planet, suggesting that a mechanism for aurora production might be universal throughout the Solar System, in spite of the vast differences between the planets.

"Here, we show the direct evidence that strongly supports the view that energetic electrons are accelerated in the near-tail region of Mercury's magnetosphere, drift rapidly toward the dawn sectors, and are subsequently injected onto closed magnetic field lines on the planetary nightside," writes a team led by astrophysicist Sae Aiwaza of the University of Pisa in Italy.

"These observations reveal that electron injections and subsequent energy-dependent drift now observed throughout the Solar System is a universal mechanism that generates aurorae despite the differences in structure and dynamics of the planetary magnetospheres."

Generally, it's thought that two things are required for the production of this kind of aurora: a magnetic field, and an atmosphere. Particles are accelerated along magnetic field lines to a polar region, where they rain down into the atmosphere. There the charged particle's interactions with other atoms and molecules releases electromagnetic radiation, some of which we might see as a a colorful glow.

The charged particles mostly come from the solar wind, although Jupiter's powerful, permanent aurorae are mostly fed by electrons from its volcanic moon Io.

But Saturn has aurorae powered by the solar wind, too, as does Uranus. Auroral features were spotted on Neptune by Voyager 2 in 1989, but we've had no subsequent detections, so we don't have a good characterization of them.

It was expected that Mars and Venus would have no aurorae, as they lack global magnetic fields, but both planets surprised us. Mars has patches of magnetism on its surface that produce localized patches of aurora in the sky. And on Venus, magnetic fields from the Sun appear to help trigger atmospheric aurorae.

Mercury has a global magnetic field, but it's pretty weak. In addition, because Mercury is so close to the Sun, it is constantly buffeted by radiation and the solar wind. So the planet has no real atmosphere to speak of; it has a thin exosphere kicked up by solar wind and micrometeoroid bombardment. This exosphere is gravitationally bound to the planet, but too diffuse to behave as a gas.

Because of this, scientists thought Mercury unlikely to have aurora. And it also has, scientists have found, a surface that occasionally fluoresces in X-rays.

© Sae Aizawa

Diagram of the electron rain observed by BepiColombo.

Aizawa and her colleagues used BepiColombo to track electrons in Mercury's vicinity, and found evidence of acceleration in the planet's magnetic field lines, precipitating towards the surface in areas, they found, that are consistent with the observed X-ray fluorescence. The fluorescence, they also found, is consistent with what we'd expect from this rain of electrons.

So, even without an atmosphere, and with a wimpy little magnetic field, Mercury seems to have found a way to create strange Mercurial aurorae, all of its very own, in minerals fluorescing X-radiation on the surface.

The research has been published in Nature Communications.

Comment: This comes on the heels of a discovery that Mercury has a magnificent comet-like tail.

The similarities between asteroids, comets, and even planets, are certainly curious; as Pierre Lescaudron writes in Earth Changes and the Human-Cosmic Connection:

Traces of this movement can be found in the late 19th century,when Scientific American published an article stating that Professor Zollner of Leipzig ascribed the 'self-luminosity' of comets to 'electrical excitement.' Zollner proposed that:

...the nuclei of comets, as masses, are subject to gravitation, while the vapors developed from them, which consist of very small particles, yield to the action of the free electricity of the sun

Then, regarding comet tails, the August 11^th 1882 issue of English Mechanic and World of Science included the following:

There seems to be a rapidly growing feeling amongst physicists that both the self-light of comets and the phenomena of their tails belong to the order of electrical phenomena.

In 1896, Nature published an article stating:

It has long been imagined that the phenomenon of comet's tails are in some way due to a solar electrical repulsion, and additional light is thrown on this subject by recent physical researches.

[...]

So, comets don't seem to be dirty snowballs after all. From the data presented above, they are glowing chunks of rock. On the other side, asteroids don't seem to be the non-glowing chunks of rocks posited by mainstream science. For example asteroids P/2013 P5 recently puzzled the whole scientific community when it started exhibiting a million miles long glowing tail. To rationalize this oddity official science claimed the asteroid was spinning so fast that it was ejecting tons of dust, while acknowledging that finally the difference between 'comets' and 'asteroids' might not be so clear-cut.¹

The fundamental difference between asteroids and comets is not their chemical composition, i.e. dirty, fluffy icy comets vs. rocky asteroids. Rather, as has long been put forward by plasma theorists, what differentiates 'comets' from 'asteroids' is their electric activity.

When the electric potential difference between an asteroid and the surrounding plasma is not too high, the asteroid exhibits a dark discharge mode² or no discharge at all. But when the potential difference is high enough, the asteroid switches to a glowing discharge mode.³ At this point the asteroid is a comet. From this perspective, a comet is simply a glowing asteroid and an asteroid is a non-glowing comet. Thus the very same body can, successively, be a comet, then an asteroid, then a comet, etc., depending on variation in the ambient electric field it is subjected to.⁴

Note that a comet can also exhibit the third plasma discharge mode, namely lightning or 'arc discharge mode', which is probably what happened when Comet Shoemaker-Levy entered the vicinity of Jupiter in July 1994:

The following article from Mr Lescaudron sheds more light on the topic: The Seven Destructive Earth Passes of Comet Venus

And check out SOTT radio's:

• Behind the Headlines: Earth changes in an electric universe: Is climate change really man-made?
• MindMatters: The Holy Grail, Comets, Earth Changes and Randall Carlson
• Behind the Headlines: The Electric Universe - An interview with Wallace Thornhill