NASA’s MAVEN Spacecraft Finds That “Stolen” Electrons Enable Unusual Aurora on Mars

The MAVEN (Mars Atmosphere and Volatile Evolution mission) team was studying Mars’ atmosphere with the Imaging UltraViolet Spectrograph (IUVS), and observed that on occasion, the ultraviolet light coming from hydrogen gas in Mars' upper atmosphere would mysteriously brighten for a few hours. They then noticed that the brightening events occurred when another MAVEN instrument, the Solar Wind Ion Analyzer (SWIA), measured enhanced solar wind protons.

Continued...
Source

Credits: NASA/MAVEN/Goddard Space Flight Center/Dan Gallagher

This animation shows a proton aurora at Mars. First, a solar wind proton approaches Mars at high speed and encounters a cloud of hydrogen surrounding the planet. The proton steals an electron from a Martian hydrogen atom, thereby becoming a neutral atom. The atom passes through the bowshock, a magnetic obstacle surrounding Mars, because neutral particles are not affected by magnetic fields. Finally, the hydrogen atom enters Mars' atmosphere and collides with gas molecules, causing the atom to emit ultraviolet light.

Source / Image Courtesy

Credits: NASA/MAVEN/University of Colorado/LASP/Anil Rao

MAVEN observations of a proton aurora. In the top panel, natural variability of the solar wind results in occasional dense flows of solar wind protons bombarding Mars. At bottom, observations by MAVEN’s Imaging Ultraviolet Spectrograph show increased ultraviolet emission from the atmosphere when the solar wind is enhanced.

Source / Image Courtesy

On Earth, the northern and southern lights occur when the solar wind (electrically charged particles from the Sun) follow our planet's geomagnetic field lines to the poles and collide with the upper atmosphere. Mars lacks a global magnetic field, so instead the solar wind piles up in front of Mars in a bow shock, which blocks charged particles from reaching the bulk of the atmosphere.