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Planetary scientists believe they can now predict the green glow of an aurora in the night sky above Mars, and they have the images to prove it.

The first observations of a visible-light aurora from the surface of the Red Planet were made by NASA's Perseverance Mars rover in 2024.

Presenting at the Europlanet Science Congress–Division of Planetary Science () joint meeting in Helsinki, Dr. Elise Wright Knutsen of the University of Oslo revealed a second snapshot of the aurora by Perseverance and, more importantly, the tools to predict when an aurora will occur on Mars.

"The fact that we captured the aurora again demonstrates that our method for predicting aurorae on Mars and capturing them works," said Knutsen, who was also the science lead for the first image of a Martian aurora seen from the ground.

Aurorae are produced when a burst of energetic particles in the solar wind, belched out by a coronal mass ejection (CME) from the sun, collide with molecules in the atmosphere, causing them to glow.

Mars's aurorae glow green as a result of the charged particles colliding with oxygen atoms high above the Red Planet, and could be bright enough that astronauts on Mars would be able to see them with the naked eye.

Furthermore, because Mars does not have a magnetic field to direct the charged particles to the magnetic poles, which is where we generally see aurorae on Earth, the Martian aurorae are seen all across the night-side of the planet at the same time as a glow in the sky. This is called "diffuse" aurora.

The same radiation that causes the aurora could also potentially be dangerous to astronauts without warning that they must take shelter, so having some idea of when a powerful solar storm will hit Mars is crucial if humans are going to one day survive on the surface.

Nonetheless, predicting aurorae on Mars is a complex business. Observations have to be planned and uploaded to the rover three days ahead once a CME bursts out in the direction of Mars. This means a lot of guesswork as to which solar storms will produce an aurora.

Knutsen's team made eight attempts to view the aurora with Perseverance's SuperCam and MastCam cameras between 2023 and 2024, and they found it to be a process of trial and error.

The first three attempts saw nothing, but by retrospectively analyzing conditions as measured by NASA's MAVEN and the ESA's Mars Express orbiters, Knutsen and her colleagues realized that the velocities of those CMEs had likely not been fast enough to create a solar wind disturbance at Mars.

"The faster the CME, the more likely it is to accelerate particles towards Mars that create aurorae, and the stronger the solar wind disturbance around Mars, the more likely it is that those particles make it into Mars's nightside atmosphere," said Knutsen. "Later, we progressively targeted faster, more intense CMEs, and that's when we found our first two detections."

The final three CMEs also didn't produce aurorae, even though they met the criteria that Knutsen was looking for.

"The last three non-detections are more curious," she said. "Statistically, there is also a degree of randomness to these things, so sometimes we're just unlucky. This perhaps isn't that surprising, since predicting the aurora on Earth down to minute precision isn't an exact science either."

Aurorae on Mars have previously been observed from orbit in ultraviolet light by ESA's Mars Express and NASA's MAVEN missions. Now, with the addition of visible-light detections, there is a growing dataset of observations for improving the accuracy of the aurora predictions. With further observations to come, they will hopefully help solve some ongoing mysteries about how the auroral lights are triggered on Mars.

"There is still much we don't understand about how aurora occur on Mars as, unlike Earth, there is no global magnetic field to guide energetic solar particles onto the nightside where the aurora can be seen," said Knutsen.

"Comparing the timing of solar wind disturbances, the arrival of solar energetic particles and the intensity and timing of aurora will advance our knowledge in this area."