Even Mercury has Geomagnetic Storms

Can other planets have geomagnetic storms, even if their magnetosphere is weak and they don’t have an ionosphere like Earth? This question has now been answered, according to research done by a team of scientists in the United States, Canada, and China.

The research team found evidence that Mercury has a ring current, part of a magnetosphere, consisting of charged particles flowing laterally in a doughnut shape around the planet but that excludes the poles. This evidence came from data obtained from the Messenger space probe while it was dropping towards the planet at the end of its mission on April 14, 2015.

A magnetosphere is a system of magnetic fields that form a bubble around a planet that is created by the spinning, electrically charged inner core of a planet. For our planet, this bubble reaches 6 to 10 times the radius of the Earth with the side opposite the Sun extending out like a comet’s tail to 60 times the radius of Earth. It extends out like that because of the force of the solar wind interacting with it.

This magnetosphere helps protect the planet from particle radiation coming from the Sun and elsewhere, and also from the solar wind which is a steady stream of charged particles emanating from the Sun. Our Sun often produces coronal mass ejections (CME), bursts of the Sun’s plasma which is a superheated gas of charged particles. The planets in our solar system, excluding Venus and Mars, have magnetospheres as well.

Earth’s magnetosphere isn’t a sphere at all. The solar wind deforms it into an asymmetrical shape. Image Credit: NASA

When a CME hits the magnetosphere it triggers a magnetic storm. According to professor Hui Zhang of the University of Alaska Fairbanks Geophysical Institute, “a magnetic storm is a major disturbance of the magnetic field in a planet’s magnetosphere.” Here on Earth, that storm causes the auroras borealis and australis, the Northern Lights and Southern Lights.

As the research team discovered from the data they collected, Mercury has magnetic storms as well. They found that Mercury’s ring current had been compressed from the CME of April 14, 2015, increasing the current’s energy. As stated in the source article, Hui Zhang says “the sudden intensification of a ring current causes the main phase of a magnetic storm.”

However, since Mercury has a very thin atmosphere no auroras are produced. Instead, the particles end up hitting the surface of the planet. Hui Zhang states that “only emissions at the X-ray and Gamma-Ray range from the surface of Mercury have been reported so far and we do not know whether there are emissions at other wavelength ranges (e.g., visible wavelengths).”

This finding may indicate that other planets, including exoplanets, with magnetospheres may also have magnetic storms. One of the research papers written about this, which was co-authored by Zhang, concludes: “The results obtained from Messenger provide a further fascinating insight into Mercury’s place in the evolution of the solar system following the discovery of its intrinsic planetary magnetic field.”


Header credit: MESSENGER image of Mercury from its third flyby (NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)