The mechanism that generates auroras may be universal throughout the solar system

2023-07-19 13:54:56

Thanks to the data collected by Bepicolombo, the joint mission of the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA), in its first approach to Mercurioa group of scientists has revealed that the mechanism that generates the auroras in the planetary magnetospheres could be universal throughout the solar system. Specifically, the study confirms that the auroras of the southern magnetosphere of this planet are similar to those observed on Earth and Mars.

Until now, it was known that the magnetosphere Mercury—the region around the planet dominated by its magnetic field—experiences rapid reconfigurations, occurring after magnetic reconnection with the solar wind, and processes similar to those observed around Earth, Jupiter, Saturn, and Uranus.

However, knowledge of reconfiguration cycles has been limited to spacecraft observations of Mercury’s northern magnetosphere, by the type of particles, and by the range of energy detected. Now, data from BepiColombo has revealed how electrons Rainfall on Mercury’s surface can trigger high-energy aurorae.

The study confirms that the auroras of the southern magnetosphere of Mercury are similar to those observed on Earth and Mars

The mission, which has been en route to the closest planet to the Sun since 2018, successfully approached Mercury for the first time on October 1, 2021. During the encounter, an international team of researchers analyzed data provided by the mission’s instruments. The results of this study are collected this week in an article published by Nature Communications.

A very fine atmosphere

According to experts, terrestrial auroras are generated 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. Since Mercury only has a very thin atmosphere, called the exosphere, its aurorae are generated by the direct interaction of the solar wind with the surface of the planet.

The BepiColombo mission consists of two spaceshipsthe ESA-led Mercury Planetary Orbiter (MPO), and the JAXA-led Mercury Magnetospheric Orbiter (MMO), which are currently in docked position for a seven-year run to final orbit of the planet.

Mercury’s auroras are generated by the direct interaction of the solar wind with the planet’s surface.

During the first encounter with Mercury, Bepicolombo came within just 200 kilometers of the planet’s surface. The observations of the plasma instruments on board one of the ships made it possible to simultaneously observe for the first time different types of charged particles from the solar wind near the planet.

“For the first time, we have witnessed how electrons are accelerated in Mercury’s magnetosphere and hurtle down onto the planet’s surface. Although Mercury’s magnetosphere is much smaller than Earth’s and has a different structure and dynamics, we can confirm that the mechanism that generates auroras is the same throughout the solar system,” he says. Sae Aizawalead author and researcher at the Institute for Research in Astrophysics and Planetology (IRAP), now at JAXA’s Institute for Space and Astronautical Sciences (ISAS) and the University of Pisa, Italy.

Observations by BepiColombo during its first approach to Mercury of electrons rushing toward the planet’s surface, correlated with the X-ray aurora locations anticipated by the MESSENGER mission. / Sae Aizawa

First contact

During the flyby, BepiColombo approached Mercury from ethe night side of the northern hemisphere and made its closest approach to the day side of the southern hemisphere. After observing the magnetosphere at this point in the southern hemisphere, it then exited this layer back into the solar wind.

Its instruments successfully observed the structure and boundaries of the magnetosphere, including the magnetopause —magnetic boundary between the magnetic field and the solar wind— and the bow shock —border region between the magnetosphere of a celestial body and the interstellar medium.

The data also showed that the magnetosphere was in an unusual state of compression, most likely due to high-pressure conditions from the solar wind.

The instruments of the BepiColombo probe successfully observed the structure and boundaries of the planet’s magnetosphere

The acceleration of the electrons appears to occur due to plasma processes on the dawn side of Mercury’s magnetosphere. High-energy electrons are transported from the tail region toward the planet, where they eventually rain down on Mercury’s surface. Unimpeded by the atmosphere, they interact with the surface material and cause the emission of X-rays, giving rise to an auroral glow.

Although NASA’s Messenger mission had already observed auroras on Mercury, the processes that trigger X-ray fluorescence by the surface’s surface had not been well understood or directly observed to date.

Reference:

Aizawa, S., Harada, Y., André, N. et al. “Direct evidence of substorm-related impulsive injections of electrons at Mercury”. Nature Communications (2023)

Rights: Creative Commons.