Newfound Martian Aurora Sheds Light on Mars’ Changing Climate

Martian proton aurora.

A type of Martian aurora first identified by NASA’s MAVEN spacecraft in 2016 is actually the most common form of aurora occurring on the Red Planet. (Image: Hans via Pixabay)

A type of Martian aurora first identified by NASA’s MAVEN spacecraft in 2016 is actually the most common form of aurora occurring on the Red Planet, according to new results from the mission. The Martian aurora is known as a proton aurora and can help scientists track water loss from Mars’ atmosphere.

On Earth, auroras are commonly seen as colorful displays of light in the night sky near the polar regions, where they are also known as the northern and southern lights. However, the proton aurora happens during the day and gives off ultraviolet light, so it is invisible to the human eye but detectable to the Imaging UltraViolet Spectrograph (IUVS) instrument on the MAVEN (Mars Atmosphere and Volatile EvolutioN) spacecraft.

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Conceptual image depicting the early Martian environment (right) – believed to contain liquid water and a thicker atmosphere – versus the cold, dry environment seen at Mars today (left).
Conceptual image depicting the early Martian environment (right) — believed to contain liquid water and a thicker atmosphere — versus the cold, dry environment seen on Mars today (left).
(Image: via NASA’s Goddard Space Flight Center)

MAVEN’s mission is to investigate how the Red Planet lost much of its atmosphere and water, transforming its climate from one that might have supported life to one that is cold, dry, and inhospitable.

Since the proton aurora is generated indirectly by hydrogen derived from Martian water that’s in the process of being lost to space, this aurora could be used to help track ongoing Martian water loss. Andréa Hughes of Embry-Riddle Aeronautical University in Daytona Beach, Florida, and lead author of the paper published in the Journal of Geophysical Research, Space Physics, said:

Different phenomena produce different kinds of auroras. However, all auroras on Earth and Mars are powered by solar activity, whether it be explosions of high-speed particles known as solar storms, eruptions of gas and magnetic fields known as coronal mass ejections, or gusts in the solar wind, a stream of electrically conducting gas that blows continuously into space at around a million miles per hour.

For example, the northern and southern lights on Earth happen when violent solar activity disturbs Earth’s magnetosphere, causing high-velocity electrons to slam into gas particles in Earth’s nightside upper atmosphere and make them glow. Similar processes generate Mars’ discrete and diffuse auroras — two types of auroras that were previously observed on the Martian nightside.

Proton auroras form when solar wind protons (which are hydrogen atoms stripped of their lone electrons by intense heat) interact with the upper atmosphere on the dayside of Mars.

As they approach Mars, the protons coming in with the solar wind transform into neutral atoms by stealing electrons from hydrogen atoms on the outer edge of the Martian hydrogen corona, a huge cloud of hydrogen surrounding the planet. When those high-speed incoming atoms hit the atmosphere, some of their energy is emitted as ultraviolet light.

This animation shows a proton aurora at Mars.
This animation shows a proton aurora. First, a solar wind proton approaches Mars at high speed and encounters a cloud of hydrogen surrounding the planet. The proton steals an electron from a Martian hydrogen atom, thereby becoming a neutral atom. The atom passes through the bowshock, a magnetic obstacle surrounding Mars, because neutral particles are not affected by magnetic fields. Finally, the hydrogen atom enters Mars’ atmosphere and collides with gas molecules, causing the atom to emit ultraviolet light. (Image: Dan Gallagher via NASA / MAVEN / Goddard Space Flight Center)

Martian auroras turn out to be common

When the MAVEN team first observed the proton aurora, they thought it was a relatively unusual occurrence. Mike Chaffin, a research scientist at the University of Colorado Boulder’s Laboratory for Atmospheric and Space Physics (LASP) and second author of the study, said:

The team has found proton auroras in about 14 percent of their dayside observations, which increases to more than 80 percent of the time when only dayside southern summer observations are considered. Nick Schneider, the co-author and lead of the IUVS team at LASP, said:

The correlation with the southern summer gave a clue as to why proton auroras are so common and how they could be used to track water loss. During the southern summer on Mars, the planet is also near its closest distance to the Sun in its orbit and huge dust storms can occur. Summer warming and dust activity appear to cause proton auroras by forcing water vapor high into the atmosphere.

Images of Mars proton aurora.
Images of Mars proton aurora. MAVEN’s Imaging Ultraviolet Spectrograph observes the atmosphere of Mars, making images of neutral hydrogen and proton aurora simultaneously (left). Observations under normal conditions show hydrogen on the disk and in the extended atmosphere of the planet from a vantage point on the nightside (middle). The proton aurora is visible as a significant brightening on the limb and disk (right); with the contribution of neutral hydrogen subtracted, the distribution of proton aurora is revealed, showing that it peaks in brightness just off the Martian disk as energetic neutrals slam into the atmosphere. (Image: Embry-Riddle Aeronautical University  /LASP, U. of Colorado)

Solar extreme ultraviolet light breaks the water into its components — hydrogen and oxygen. The light hydrogen is weakly bound by Mars’ gravity and enhances the hydrogen corona surrounding Mars, increasing hydrogen loss to space. More hydrogen in the corona makes interactions with solar-wind protons more common, making proton auroras more frequent and brighter. Hughes concluded:

Provided by: Bill Steigerwald / Nancy Jones,  [Note: Materials may be edited for content and length.]

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