MAVEN and EMM are the first to observe Mars' patchy proton aurora


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 show the typical atmospheric conditions, in which the EMM instrument EMUS 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. Credit: EMM/EMUS
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 show the typical atmospheric conditions, in which the EMM instrument EMUS 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. Credit: EMM/EMUS

The MAVEN (Mars Atmosphere and Volatile Evolution) project of NASA and the Emirates Mars Mission (EMM) of the United Arab Emirates have revealed cooperative observations of dynamic proton aurora occurrences on Mars. EMM's remote auroral observations, along with MAVEN's in-situ plasma investigations, bring up new paths for comprehending the Martian atmosphere. This collaboration was enabled by recent data exchange between the two missions, and it emphasizes the importance of multi-point observations in space. These findings were published in the journal Geophysical Research Letters.


EMM observed fine-scale features in proton aurora that spanned the whole day side of Mars in the latest research. MAVEN detected proton aurora in 2018, which is a type of Martian aurora formed when the solar wind, which is made up of charged particles from the Sun, interacts with the upper atmosphere. Typical proton aurora measurements by MAVEN and the ESA's Mars Express mission indicate this aurora to be smooth and equally dispersed over the globe. EMM, on the other hand, saw proton aurora which looked to be very dynamic and varied. When turbulent circumstances surrounding Mars allow charged particles to flow directly into the atmosphere and light when they calm down, these "patchy proton aurora" emerge.


According to Mike Chaffin, a MAVEN and EMM scientist based at the University of Colorado Boulder's Laboratory for Atmospheric and Space Physics and the study's lead author, "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 where the solar wind was directly impacting the upper atmosphere wherever we observed auroral emission." We can corroborate this idea and verify that what we were seeing was basically a map of where the solar wind was showering down on the earth by integrating EMM auroral observations with MAVEN measurements of the auroral plasma environment.

Normally it is difficult for the solar wind to reach Mars' upper atmosphere because it is diverted by the bow shock and magnetic fields around the planet. The patchy proton aurora measurements are therefore a window into the unusual case where the Mars-solar wind interaction is chaotic.


The complete impact of these circumstances on the Martian atmosphere, according to Chaffin, is unclear, but EMM and MAVEN data will be critical in comprehending these mysterious phenomena.

Top image shows the normal proton aurora formation mechanism first discovered in 2018. White lines show that solar wind protons traveling away from the Sun are normally swept around the planet by the Mars magnetosphere, and don't directly interact with the atmosphere. When proton aurora occur, a small fraction of the solar wind collides with Mars hydrogen in the extended corona of the planet (shown in blue), and charge exchanges into neutral H atoms. These newly created H atoms are still traveling at the same speed, and are no longer sensitive to the magnetospheric forces that redirect protons around the planet. Instead, the energetic H atoms slam directly into the upper atmosphere of Mars and collide multiple times with the neutral atmosphere, resulting in auroral emission by the incident H atoms (purple). Because the solar wind and Mars corona are uniform across the planet, the aurora occurs everywhere on the planet's day side with a uniform brightness. Bottom image shows the newly discovered formation mechanism for patchy proton aurora. Green lines in the top image show that under normal conditions the solar wind magnetic field drapes nicely around the planet. By contrast, patchy proton aurora form during unusual circumstances when the solar wind magnetic field is aligned with the proton flow. Under such conditions the typical draped magnetic field configuration is replaced by a highly variable patchwork of plasma structures, and the solar wind is able to directly impact the planet's upper atmosphere in specific locations that depend on the structure of the turbulence. When incoming solar wind protons collide with the neutral atmosphere, they can be neutralized and emit aurora in localized patches. During such times patchy proton aurora forms a map of the locations where solar wind plasma is directly impacting the planet. Credit: Emirates Mars Mission/UAE Space Agency
Top image shows the normal proton aurora formation mechanism first discovered in 2018. White lines show that solar wind protons traveling away from the Sun are normally swept around the planet by the Mars magnetosphere, and don't directly interact with the atmosphere. When proton aurora occur, a small fraction of the solar wind collides with Mars hydrogen in the extended corona of the planet (shown in blue), and charge exchanges into neutral H atoms. These newly created H atoms are still traveling at the same speed, and are no longer sensitive to the magnetospheric forces that redirect protons around the planet. Instead, the energetic H atoms slam directly into the upper atmosphere of Mars and collide multiple times with the neutral atmosphere, resulting in auroral emission by the incident H atoms (purple). Because the solar wind and Mars corona are uniform across the planet, the aurora occurs everywhere on the planet's day side with a uniform brightness. Bottom image shows the newly discovered formation mechanism for patchy proton aurora. Green lines in the top image show that under normal conditions the solar wind magnetic field drapes nicely around the planet. By contrast, patchy proton aurora form during unusual circumstances when the solar wind magnetic field is aligned with the proton flow. Under such conditions the typical draped magnetic field configuration is replaced by a highly variable patchwork of plasma structures, and the solar wind is able to directly impact the planet's upper atmosphere in specific locations that depend on the structure of the turbulence. When incoming solar wind protons collide with the neutral atmosphere, they can be neutralized and emit aurora in localized patches. During such times patchy proton aurora forms a map of the locations where solar wind plasma is directly impacting the planet. Credit: Emirates Mars Mission/UAE Space Agency

Scientists have been able to establish the causes of the patchy proton aurora thanks to data exchange between MAVEN and EMM. The Emirates Mars Ultraviolet Spectrograph (EMUS) instrument is aboard EMM, and it scans the Red Planet's upper atmosphere and exosphere for variations in atmospheric composition and atmospheric escape to space. MAVEN is equipped with a comprehensive suite of plasma instruments, including the Magnetometer (MAG), the Solar Wind Ion Analyzer (SWIA), and the SupraThermal And Thermal Ion Composition (STATIC) instrument utilized in this study.


According to Shannon Curry of UC Berkeley's Space Sciences Laboratory, MAVEN Principal Investigator, EMM's global observations of the upper atmosphere give a unique viewpoint on an area essential to MAVEN science. These kinds of simultaneous observations delve into the underlying physics of atmospheric dynamics and development, highlighting the advantages of worldwide scientific collaboration.


Hessa Al Matroushi, EMM Science Lead, concurred.


She stated that access to MAVEN data was critical for contextualizing these new EMM findings. We're pushing the limits of our present knowledge of not only Mars but also planetary interactions with the solar wind.


Measurements from several perspectives have previously proved useful in Earth and heliophysics studies. Over a half-dozen, Mars orbiters are already collecting scientific data, and with the southern hemisphere of Mars presently experiencing summer, when proton aurora is believed to be most active, multi-vantage-point observations will be important to understand how these phenomena arise. The partnership of EMM and MAVEN underscores the importance of discovery-level science concerning the Martian atmosphere with two spacecraft monitoring the same location at the same time.


Journal Information: 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 (2022). DOI: 10.1029/2022GL099881
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