MAVEN: “Stolen” Electrons Enable Unusual Aurora on Mars

[bystander]

MAVEN Finds That “Stolen” Electrons Enable Unusual Aurora on Mars
NASA | GSFC | MAVEN | University of Colorado, Boulder | 2018 Jul 23

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. (Credits: NASA/GSFC/MAVEN/Dan Gallagher)

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Auroras appear on Earth as ghostly displays of colorful light in the night sky, usually near the poles. Our rocky neighbor Mars has auroras too, and NASA’s MAVEN spacecraft just found a new type of Martian aurora that occurs over much of the day side of the Red Planet, where auroras are very hard to see.

Auroras flare up when energetic particles plunge into a planet’s atmosphere, bombarding gases and making them glow. While electrons generally cause this natural phenomenon, sometime protons can elicit the same response, although it’s more rare. Now, the MAVEN team has learned that protons were doing at Mars the same thing as electrons usually do at Earth—create aurora. This is especially true when the Sun ejects a particularly strong pulse of protons, which are hydrogen atoms stripped of their lone electrons by intense heat. The Sun ejects protons at speeds up to two million miles per hour (more than 3 million kilometers per hour) in an erratic flow called the solar wind.

The MAVEN 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.

But two puzzles make this type of aurora seem impossible at first glance: how did these protons get past the planet’s “bow shock,” a magnetic obstacle which normally diverts the solar wind’s charged particles around the planet? And how could the protons give off light, since atoms need electrons to do so? ...

Discovery of a Proton Aurora at Mars - Justin Deighan et al

• Nature Astronomy (online 23 Jul 2018) DOI: 10.1038/s41550-018-0538-5

[bystander]

Newfound Martian Aurora Actually the Most
Common; Sheds Light on Mars’ Changing Climate
NASA | GSFC | MAVEN | University of Colorado, Boulder | 2019 Dec 12

MAVEN images of the Martian atmosphere under normal conditions (left) and with an aurora (middle and right). (Credit: Embry-Riddle Aeronautical University/LASP, CU)

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A type of Martian aurora first identified by NASA’s MAVEN spacecraft in 2016 is actually the most common form of aurora occurring on the Red Planet, according to new results from the mission. The aurora is known as a proton aurora and can help scientists track water loss from Mars’ atmosphere.

At Earth, aurora are commonly seen as colorful displays of light in the night sky near the polar regions, where they are also known as the northern and southern lights. However, the proton aurora on Mars happens during the day and gives off ultraviolet light, so it is invisible to the human eye but detectable to the Imaging UltraViolet Spectrograph (IUVS) instrument on the MAVEN (Mars Atmosphere and Volatile EvolutioN) spacecraft.

MAVEN’s mission is to investigate how the Red Planet lost much of its atmosphere and water, transforming its climate from one that might have supported life to one that is cold, dry, and inhospitable. Since the proton aurora is generated indirectly by hydrogen derived from Martian water that’s in the process of being lost to space, this aurora could be used to help track ongoing Martian water loss. ...

Proton Aurora on Mars: A Dayside Phenomenon Pervasive in Southern Summer ~ Andréa Hughes et al

• Journal of Geophysical Research, Space Physics (online 12 Oct 2019) DOI: 10.1029/2019JA027140