Thanks to a collaboration between two orbiting space probes, we have a new understanding of the marvelous phenomenon of Mars.
NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) and the United Arab Emirates’ Hope Probe have teamed up to study the ultraviolet proton auroras dancing and glowing in the Martian atmosphere.
The new research shows that these daytime events are not always scattered, featureless and evenly distributed, but are highly dynamic and variable, containing fine-scale structures.
“Observations by the EMM (UAE Mars Mission) show that the auroras are so extensive and disorganized that the plasma environment around Mars must have been truly disturbed, so that the solar wind directly affects the upper atmosphere where we observe auroral emission,” said Mike Chaffin, a planetary scientist at the University of Colorado Boulder.
“By combining EMM auroral observations with MAVEN’s measurements of the auroral plasma environment, we can confirm this hypothesis and determine that what we are seeing is essentially a map of the solar wind and rain falling on Earth.”
Proton aurora — the most common auroras on the Red Planet — were first described in 2018, as shown by the MAVEN data. They form very similarly to how auroras form on Earth; however, since Mars is a very different beast and doesn’t have an internal driving magnetosphere like Earth, the end result is unique to Mars.
The closest thing the red planet has to the global magnetic field is a fragile magnetic field caused by the hum of charged particles slowing down as they hit the atmosphere. Although it is weak, it is usually strong enough to deflect many high-speed protons and neutrons falling from the sun.
Proton auroras form when positively charged protons in the solar wind collide with Mars’ hydrogen envelope and are ionized, stealing electrons from hydrogen atoms to become neutral.
This charge exchange allows neutral particles to bypass the bow shock of the magnetic field around Mars, rain and emit ultraviolet light in the upper atmosphere.
This process is thought to reliably produce uniform auroral emission during the Martian day. New observations suggest otherwise.
Rather than the expected smooth profiles, it is hoped that the detector’s data show that sometimes auroras are incomplete, suggesting that there may be unknown processes in the formation of these auroras.
This is where MAVEN comes into play. NASA’s orbiter carries a full suite of plasma instruments to probe the solar wind, magnetic environment and thermions in the space around Mars.
While Hope was photographing the strange aurora, it was measured at the same time, and the combined data allowed scientists to reconstruct what was behind it.
“By examining observations of patchy auroras with varying shapes and locations from multiple Emirates Mars missions, and combining these images with plasma measurements from NASA’s Mars Atmosphere and Volatile Evolution mission, we concluded , many processes can produce patchy auroras,” the researchers wrote in their paper.
“This mottled aurora is primarily the result of plasma turbulence, which in some cases causes the solar wind to deposit directly throughout the Martian day.”
In other words, a rare chaotic interaction between Mars and the solar wind is responsible for the patchy auroras. Although it’s not entirely clear what the impact on the surface of Mars will be.
However, this could have implications for long-term atmospheric and water loss; without a global magnetic field, Mars would continue to lose both.
Interestingly, proton auroras—whether smooth or mottled—may help us understand at least one of them, since the hydrogen involved is partly created by water in the Martian atmosphere leaking into space.
“Many future data and modeling studies will be required to tease out the full impact of these conditions on the evolution of the Martian atmosphere,” the researchers wrote.
The research has been published in geophysical research letters.