The Emirates Mars Mission, the Arab world’s first interplanetary exploration, has made the first observations of a new type of proton aurora around Mars. The spatially variable ‘patchy’ proton aurora could provide new insights into unexpected Martian atmospheric behavior. To fully characterize these observations, the EMM team collaborated with NASA’s MAVEN (Mars Atmosphere and Volatile EvolutioN) mission. The combination of EMM’s unprecedented global aurora images and MAVEN’s concurrent local plasma observations opens up new avenues for understanding Mars’ enigmatic aurora.
“Our discovery of these patchy proton aurora adds a new kind of event to the long list of those currently studied by EMM and challenges our existing views of how the proton aurora on Mars’ dayside are formed,” said Hessa Al Matroushi, EMM’s Science Lead. “The EMM Hope probe has so far uncovered many unexpected phenomena that extend our understanding of Mars’ atmospheric and magnetospheric dynamics. These new observations, combined with MAVEN data, have lifted the lid on entirely new possibilities for scientific research.”
When the solar wind directly impacts Mars’ dayside upper atmosphere and emits ultraviolet light as it slows down, a new patchy type of proton aurora forms. It was discovered in dayside disk snapshots obtained by the Emirates Mars Ultraviolet Spectrometer (EMUS), which monitors the planet’s upper atmosphere and exosphere for variability in atmospheric composition and atmospheric escape to space.
The aurora appears as bright regions spread across the planet’s dayside in two ultraviolet wavelengths associated with the Hydrogen atom, Lyman beta at 102.6 nm and Lyman alpha at 121.6 nm. Under normal conditions, the planet’s dayside disk is uniform at these wavelengths, and the planetary brightness is caused by Hydrogen atoms scattering sunlight. Small regions of the planet become much brighter at these wavelengths when the aurora occurs, indicating intense localized energy deposition in the atmosphere.
“We’ve seen emissions at these wavelengths before, thanks to proton aurora studies by NASA’s MAVEN mission, but these EMM EMUS images represent the first time we’ve had a global view of spatial variability in proton aurora at Mars, and the first time we’ve been able to unambiguously observe this patchy structure,” said EMM science team member and lead author of a newly submitted paper on the proton aurora, Mike Chaffin. “We know that these wavelengths are only emitted by the Hydrogen atom, which tells us that super energetic Hydrogen atoms must be present in the atmosphere in order to produce the auroral emission.”
A data sharing agreement between EMM and MAVEN allowed the new EMM images to be analyzed using MAVEN plasma observations, which have been characterizing the Mars ionosphere and magnetosphere since 2014. MAVEN is equipped with a full suite of plasma instruments, including a magnetometer and two ion electrostatic analysers, which were used to measure the Martian plasma and field environment during EMM’s observations of patchy proton aurora events.
“Multi-vantage point measurements of the Martian atmosphere tell us about the real time response of the atmosphere to the Sun. These types of simultaneous observations probe the fundamental physics of atmospheric dynamics and evolution”, said MAVEN Principal Investigator Shannon Curry.
“Access to MAVEN data has been essential for placing these new observations into a wider context. Together, we’re pushing the boundaries of our existing knowledge not only of Mars, but of planetary interactions with the solar wind,” said Al Matroushi.
Martian proton auroras were originally discovered by MAVEN and subsequently found in data from ESA’s Mars Express mission, but most of these previous observations show uniform auroral emission across the dayside of the planet. By contrast, the EMUS observations are able to unambiguously reveal small-scale spatial structure. Scientists from both teams now believe the patchy aurora can only be produced by plasma turbulence in the space surrounding Mars. “Because of the size scales involved in the solar wind and extended hydrogen atmosphere of Mars, there’s no way the standard proton aurora formation mechanism could produce the aurora we’re observing with EMUS,” said Chaffin.
“In the August 11 observations the aurora is so widespread and so disorganized that the plasma environment around Mars must have been truly disturbed. Thanks to MAVEN measurements of the Mars plasma environment simultaneous with the aurora, we can confidently say that the solar wind is directly impacting the upper atmosphere wherever we’re seeing auroral emission,” he added. “What we’re seeing is essentially a map of where the solar wind is raining down onto the planet.”
Hope’s observations of patchy proton aurora and MAVEN’s measurements of plasma conditions provide a window into rare circumstances in which the interaction between Mars and the solar wind is unusually chaotic.
Hope has seen patchy aurora multiple times during its mission, and the shape of the aurora is not always the same. For example, on August 30, 2021, the patchy proton aurora was confined to a much smaller portion of the disk than on August 11, indicating that a different mechanism is at work. At Mars, plasma turbulence can occur under a variety of conditions, and different shapes of patchy proton aurora can reveal different plasma conditions.
As of June 2022, Mars is about a month away from the peak of its Southern Summer, when proton aurora are known to be at their most active. “Whether we’ll see anything as spectacular as what we’ve already got is anyone’s guess, but I’m hopeful. Hope continues to far exceed our expectations for scientific discovery, and I can’t wait to see what we learn next.” said Chaffin.
The top image depicts the normal proton aurora formation mechanism, which was first discovered in 2018. Solar wind protons traveling away from the Sun are normally swept around the planet by the Mars magnetosphere and do not interact directly with the atmosphere. When a small fraction of the solar wind collides with Mars hydrogen in the planet’s extended corona (shown in blue), charge exchanges into neutral H atoms.
These newly formed H atoms continue to travel at the same speed and are no longer affected by magnetospheric forces that redirect protons around the planet. Instead, the energetic H atoms slam directly into Mars’ upper atmosphere and collide with the neutral atmosphere multiple times, 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 with uniform brightness everywhere on the planet’s day side.
The bottom image depicts the newly discovered mechanism for patchy proton aurora formation. The green lines in the top image show how the solar wind magnetic field drapes nicely around the planet under normal conditions. Patchy proton auroras, on the other hand, form when the solar wind magnetic field is aligned with the proton flow.
The typical draped magnetic field configuration is replaced by a highly variable patchwork of plasma structures under such conditions, and solar wind can directly impact the planet’s upper atmosphere in specific locations that depend on the structure of the turbulence. When protons from the incoming solar wind collide with the neutral atmosphere, they can be neutralized and emit aurora in patches. Patchy proton aurora forms a map of the locations where solar wind plasma is directly impacting the planet at such times.
Hope’s EMUS (Emirates Mars Ultraviolet Spectrometer) instrument measures the Martian disk in the far and extreme ultraviolet, with the primary science goal of measuring oxygen and carbon monoxide in Mars’ thermosphere and hydrogen and oxygen variability in the exosphere.
The spectrometer’s high sensitivity, which is required to detect the distant oxygen corona, has resulted in EMUS being an extremely effective detector of auroral activity across the planet, unearthing new understandings of the nightside discrete aurora and the discovery of a completely new auroral phenomenon, the sinuous discrete aurora, which can stretch over halfway across the planet.
Hope is following its planned 20,000 – 43,000 km elliptical science orbit, with an inclination to Mars of 25 degrees. The probe completes one orbit of the planet every 55 hours and captures a full planetary data sample every nine days throughout its two-year mission to map Mars’ atmospheric dynamics.
EMM and the Hope probe are the culmination of a knowledge transfer and development effort started in 2006, which has seen Emirati engineers working with partners around the world to develop the UAE’s spacecraft design, engineering and manufacturing capabilities. Hope is a fully autonomous spacecraft, carrying three instruments to measure Mars’ atmosphere. Weighing some 1,350 kg, and approximately the size of a small SUV, the spacecraft was designed and developed by MBRSC engineers working with academic partners, including LASP at the University of Colorado, Boulder; Arizona State University and the University of California, Berkeley.
The Emirates Mars Mission is studying the Martian atmosphere and the relationship between the upper layer and lower regions and, for the first time, gives the international science community full access to a holistic view of the Martian atmosphere at different times of the day, through different seasons. Science data releases have been taking place every three months, with the information made freely accessible globally to researchers and enthusiasts,
The Hope Probe’s historic arrival at the Red Planet coincided with a year of celebrations to mark the UAE’s Golden Jubilee in 2021.
