Solar wind whips up Mercury’s poles

U. MICHIGAN (US) — Sodium and oxygen particles kicked up by a blistering solar wind at Mercury’s poles are the primary components of the planet’s wispy atmosphere, according to data from NASA’s Messenger spacecraft.

The Fast Imaging Plasma Spectrometer (FIPS), made by scientists at the University of Michigan, has taken the first global measurements of Mercury’s exosphere and magnetosphere in an effort to better understand how the closest planet to the Sun interacts with its fiery neighbor.

The measurements, reported in Science, confirmed scientists’ theories about the composition and source of the particles in Mercury’s space environment that become charged in a mechanism that’s similar to the one that generates the Aurora Borealis on Earth.

Planet Mercury as seen from the Messenger spacecraft in 2008. (Credit: NASA)

“We had previously observed neutral sodium from ground observations, but up close we’ve discovered that charged sodium particles are concentrated near Mercury’s polar regions where they are likely liberated by solar wind ion sputtering, effectively knocking sodium atoms off Mercury’s surface,” says Thomas Zurbuchen, professor of atmospheric, oceanic and space sciences and aerospace engineering.

Earth and Mercury are the only terrestrial planets with global-scale magnetic fields. The solar wind is a squall of hot plasma, or charged particles, continuously emanating from the Sun.

Earth, which has a relatively strong magnetosphere, can shield itself from most of the solar wind. Mercury, which has a comparatively weak magnetosphere and is 2/3 closer to the Sun, is a different story.

“Our results tell us is that Mercury’s weak magnetosphere provides very little protection of the planet from the solar wind,” Zurbuchen says.

Studying Mercury’s magnetosphere and space environment helps scientist understand fundamental science about the Sun.

“We’re trying to understand how the Sun, the granddaddy of all that is life, interacts with the planets,” says Jim Raines, doctoral candidate and FIPS operations engineer.

“It is Earth’s magnetosphere that keeps our atmosphere from being stripped away. And that makes it vital to the existence of life on our planet.”

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Correction: The article originally stated Earth and Mercury are the only two magnetized planets in the solar system, and as such, can somewhat deflect the solar wind around them. That statement was changed to the following: “Earth and Mercury are the only terrestrial planets with global scale magnetic fields.”