We have new insight into a remarkable Martian phenomenon, thanks to a collaboration between two orbiting space probes.
NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) and the United Arab Emirates’ Hope Probe have joined forces to study the ultraviolet proton auroras that dance and glow high in the Martian atmosphere.
The new research reveals that these daily events are not always diffuse, featureless and uniformly distributed, but highly dynamic and variable, containing fine structures.
“Observations by the EMM (Emirates Mars Mission) suggest that the aurora is so widespread and disorganized that the plasma environment around Mars must have been truly disturbed, to the extent that the solar wind acted directly on the upper atmosphere where and have observed auroral emissions,” says planetary scientist Mike Chaffin of the University of Colorado Boulder.
“By combining EMM auroral observations with MAVEN measurements of the auroral plasma medium, we can confirm this hypothesis and determine that what we see is essentially a map of where the solar wind is raining down on the planet.”
Proton auroras – the red planet’s most common aurora – were first described in 2018, as seen in MAVEN data. They form quite similarly to how auroras form on Earth; however, since Mars is a very different beast, without an internally driven magnetosphere like Earth’s, the end result is unique to Mars.
The closest thing to a global magnetic field the Red Planet has is a brittle field caused by the hum of charged particles slowing down as they hit the atmosphere. However weak it is, it is usually enough to deflect many of the high-speed protons and neutrons falling from the Sun.
Proton auroras form when positively charged protons in the solar wind collide with Mars’ hydrogen shell and ionize, stealing electrons from hydrogen atoms to become neutral.
This exchange of charge allows the neutral particles to bypass the impact of the magnetic field around Mars, rain down into the upper atmosphere and emit ultraviolet light.
This process was thought to reliably produce uniform auroral radiation over the dayside of Mars. New observations suggest otherwise.
Instead of the expected smooth profile, the Hope Probe data show that the aurora is sometimes patchy, suggesting that there may be unknown processes during the formation of these auroras.
This is where MAVEN comes into the picture. NASA’s orbiter carries a full suite of plasma instruments to study the solar wind, magnetic environment and thermal ions in space around Mars.
He simultaneously took measurements while Hope imaged the strange glows, and the combined data allowed scientists to reconstruct the cause.
“By examining multiple Emirates Mars Mission observations of patchy auroras that have different shapes and locations, and combining these images with plasma measurements made by NASA’s Mars Atmosphere and Volatile Evolution mission, we conclude that a number of processes can produce irregular auroras,” the researchers wrote in their paper.
“This patchy glow is mostly the result of plasma turbulence, which under certain circumstances leads to direct deposition of the solar wind throughout the Martian day.”
In other words, a rare chaotic interaction between Mars and the solar wind is responsible for the patchy glow; although it is not entirely clear what the impact is on the Martian surface.
However, there may be implications for long-term atmospheric and water loss; without a global magnetic field, Mars continues to lose both.
Interestingly, proton auroras—both smooth and patchy—can help us understand at least one of these, since the hydrogen involved is partially created by water in the Martian atmosphere escaping into space.
“Much future data and modeling studies will be needed,” the researchers wrote, “to understand the full implications of these conditions for the evolution of the Martian atmosphere.”
The study was published in Geophysical Research Letters.