Thursday, September 29, 2022

MAVEN and EMM Orbiters Observe ‘Patchy’ Proton Aurora on Mars

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Even though Mars does not have a global magnetic field like the Earth, it still possesses multiple kinds of aurora. One of these is proton aurora, which is thought to form mainly by an indirect process that allows a small fraction of the solar wind to rain down on the Red Planet uniformly across the dayside. Now, NASA’s MAVEN (Mars Atmosphere and Volatile EvolutioN) mission and UAE’s Emirates Mars Mission (EMM) have spotted ‘patchy’ proton aurora on Mars. This type of aurora is mostly the result of plasma turbulence, which under some circumstances leads to direct deposition of the solar wind across the entire Martian dayside, with a potentially large impact on long term atmosphere and water loss from the planet.

Patchy proton aurora on Mars form when turbulent conditions around the planet allow charged hydrogen particles from the Sun to stream into the Martian atmosphere. Images from August 5, 2021, show the typical atmospheric conditions, in which EMM’s EMUS instrument detects no unusual activity at two wavelengths associated with the hydrogen atom. But on August 11 and August 30, the instrument observed patchy aurora at both wavelengths, indicating turbulent interactions with the solar wind. Image credit: EMM / EMUS / UAE Space Agency.

First discovered by MAVEN in 2018, proton aurora is a type of Martian aurora that forms as the solar wind, made up of charged particles from the Sun, interacts with the planet’s upper atmosphere.

Typical proton aurora observations made by MAVEN and ESA’s Mars Express mission show this aurora appearing smooth and evenly distributed across the hemisphere.

By contrast, EMM observed proton aurora that appeared highly dynamic and variable.

This patchy proton aurora forms when turbulent conditions around Mars allow the charged particles to flood directly into the atmosphere and glow as they slow down.

“EMM’s observations suggested that the aurora was so widespread and disorganized that the plasma environment around Mars must have been truly disturbed, to the point that the solar wind was directly impacting the upper atmosphere wherever we observed auroral emission,” said MAVEN/EMM scientist Dr. Mike Chaffin, a researcher at the University of Colorado Boulder.

“By combining EMM auroral observations with MAVEN measurements of the auroral plasma environment, we can confirm this hypothesis and determine that what we were seeing was essentially a map of where the solar wind was raining down onto the planet.”

Comparison of normal and patchy proton aurora formation mechanisms at Mars. Top image shows the normal proton aurora formation mechanism. Bottom image shows the newly discovered formation mechanism for patchy proton aurora. Image credit: EMM / UAE Space Agency.

Normally it is difficult for the solar wind to reach Mars’ upper atmosphere because it is redirected by the bow shock and magnetic fields surrounding the planet.

The patchy proton aurora observations are therefore a window into rare circumstances — ones during which the Mars-solar wind interaction is chaotic.

“The full impact of these conditions on the Martian atmosphere is unknown, but EMM and MAVEN observations will play a key role in understanding these enigmatic events,” Dr. Chaffin said.

The new data from several instruments aboard MAVEN and EMM orbiters enabled Dr. Chaffin and colleagues to determine the drivers behind the patchy proton aurora.

“EMM’s global observations of the upper atmosphere provide a unique perspective on a region critical to MAVEN science,” said MAVEN principal investigator Dr. Shannon Curry, a researcher at the University of California, Berkeley.

“These types of simultaneous observations probe the fundamental physics of atmospheric dynamics and evolution and highlight the benefits of international scientific collaboration.”

The findings were published in the journal Geophysical Research Letters.

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Michael S. Chaffin et al. Patchy Proton Aurora at Mars: A Global View of Solar Wind Precipitation Across the Martian Dayside From EMM/EMUS. Geophysical Research Letters, published online August 31, 2022; doi: 10.1029/2022GL099881

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