In a joint effort by NASA’s MAVEN spacecraft and the United Arab Emirates’ Emirates Mars Mission (EMM), scientists have observed an unusually chaotic interaction between the solar wind and the upper Martian atmosphere, producing a unique ultraviolet aurora. The phenomenon represents an unusual occurrence in Martian space weather, and scientists look forward to using future collaborations between spacecraft to keep an eye out for repeat events.
The strange, patchy aurora created by the solar wind has been observed twice, on August 11 and August 30 of this year. Similar auroras have been observed regularly since 2018, but they usually appear in a smooth, even band covering the planet. Last month’s auroras, in contrast, were patchy, variable, and localized.
It’s a specific type of aurora called the proton aurora, and it occurs on the planet’s dayside when hydrogen atoms from the sun, stripped of their electrons, shoot toward the red planet and the “arc shock,” a magnetic barrier , penetrate naturally shields the Martian atmosphere. Some of the protons are able to sidestep the bow thrust by stealing electrons from the busy region of space around Mars, becoming neutral and breaking through to hit the upper atmosphere. The result is an ultraviolet aurora that previously appeared to appear as a coherent whole on Mars, but is now seen in patches.
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Proton auroras also occur on Earth, but they are invisible to the human eye and less common due to Earth’s stronger magnetic field.
The top image shows the normal formation mechanism for proton aurora first discovered in 2018. The lower image shows the newly discovered formation mechanism for splotchy proton auroras. Credits: Emirates Mars Mission/UAE Space Agency.
It took observations from both Maven and EMM to understand what was going on. EMM’s Emirates Mars Ultraviolet Spectrograph (EMUS) instrument is constantly scanning the planet’s upper atmosphere, looking for signs of atmospheric leakage into space and changes in composition. Its detector is perfect for capturing the ultraviolet light caused by the proton aurora.
MAVEN, on the other hand, collects in situ data and “feels” the plasma of the solar wind as it passes using a magnetometer and ion analyzers.
When data from EMM was compared to that from MAVEN, it was clear that the splotchy proton aurora was the result of a severely disturbed plasma environment at the time of the events.
Mike Chaffin of the University of Colorado Boulder explained: “The EMM’s observations suggested that the aurora was so widespread and disorganized that the plasma environment around Mars must have been really disturbed, to the point where the solar wind directly affecting the upper atmosphere wherever we observed aurora emission… By combining EMM auroral observations with MAVEN measurements of the auroral plasma environment, we can confirm this hypothesis and state that what we saw is essentially was a map where the solar wind rained on the planet.”
Images from August 5 show typical atmospheric conditions (no unusual activity). On August 11 and 30, the instrument observed patchy auroras indicating turbulent interactions with the solar wind.
Essentially, it was a temporary breakdown in Mars’ natural defenses against solar radiation as particles were able to take advantage of chaotic space weather to find a way into the planet’s atmosphere.
MAVEN arrived on Mars in 2014 and was supported by EMM in 2021. There are more than half a dozen probes orbiting Mars, each with different specializations and abilities. By working together, they can help us understand Mars in ways they couldn’t alone, including studying its unique auroras.
Evan Gough: “Mars also has auroras, we just can’t see them.” Universe today.
Willow Reed, “MAVEN and EMM Make First Observations of Mottled Proton Aurora on Mars.” NASA.
Bill Steigerwald/Nancy Jones, “NASA’s MAVEN Spacecraft Finds ‘Stolen’ Electrons Enable Unusual Aurora on Mars.” NASA.