We’ve all heard of the majestic North Lights which sometimes sweep Earth’s atmosphere in a dazzling light show. But did you know Mars has auroras, too? Scientists first learned about them in 2016. Now, a new study suggests that Martian auroras are not at all rare as previously thought. In fact, they sometimes occur nearly on a daily basis. Unlike their Earthen counterparts, however, you’d need some ultraviolet goggles to see the Martian aurora.
Auroras are nature’s own dynamic light show. These are created by charged particles from the Sun traveling along Earth’s magnetic field lines and exciting our atmosphere. The interaction causes electrons and protons to ionize different compounds in the atmosphere, causing the sky to light up in red and green tints. In the North, these displays are called aurora borealis (or the northern lights), named after the Roman goddess of dawn, Aurora, and the Greek name for the north wind, Boreas.
The physical interaction that produces the lights was first demonstrated by Norwegian physicist Kristian Birkeland almost a century ago when he produced his own auroras in the lab. In his world-famous experiment, he demonstrated how the lights form around magnetic spheres inside a small vacuum chamber. A modern-day version of this experiment is called the Planeterrella, whose inner workings are explained in this great video produced by the University of Leicester, embedded below.
In 2016, NASA’s MAVEN spacecraft observed auroras on Mars for the first time. Unlike Earthen auroras, the Martian variety is triggered exclusively by protons and occurs during the day. What’s more, the lights are emitted only in the ultraviolet spectrum, meaning you can’t see them with the naked eye — but MAVEN’s instruments sure can.
“At first, we believed that these events were rather rare because we weren’t looking at the right times and places,” said Mike Chaffin, who is a planetary scientist at the University of Colorado Boulder. “But after a closer look, we found that proton aurora are occurring far more often in dayside southern summer observations than we initially expected.”
Martian auroras are formed when the solar wind strikes Mars’ thin atmosphere, stripping away electrons from hydrogen atoms, which are now basically just protons. These protons collide with the planet’s hydrogen corona — an envelope of hydrogen gas surrounding the red planet, which is linked to water loss on Martian surface — stealing electrons, becoming a whole atom again. In the process, the hydrogen atom slams into the Martian atmosphere, colliding with other gas molecules and emitting ultraviolet light.
“Perhaps one day, when interplanetary travel becomes commonplace, travelers arriving at Mars during southern summer will have front-row seats to observe Martian proton aurora majestically dancing across the dayside of the planet (while wearing ultraviolet-sensitive goggles, of course). These travelers will witness firsthand the final stages of Mars losing the remainder of its water to space,” said Andréa Hughes of Embry-Riddle Aeronautical University in Daytona Beach.
In their new study, Chaffin and colleagues found proton aurora on Mars occur far more often in the dayside southern summer than initially expected. Measurements suggest that proton aurora occurs in about 14% of dayside observations, increasing to nearly 80% of observations when considering only dayside southern summer observations.
Because auroras and water loss on Mars are linked due to the hydrogen cycle, scientists are very interested in studying this phenomenon. Mars is closest to the Sun during its southern summer, and this sudden influx of solar wind could explain the new observations.
“All the conditions necessary to create Martian proton aurora (e.g., solar wind protons, an extended hydrogen atmosphere, and the absence of a global dipole magnetic field) are more commonly available at Mars than those needed to create other types of aurora,” said Hughes. “Also, the connection between MAVEN’s observations of increased atmospheric escape and increases in proton aurora frequency and intensity means that proton aurora can actually be used as a proxy for what’s happening in the hydrogen corona surrounding Mars, and therefore, a proxy for times of increased atmospheric escape and water loss.”