The northern lights are fleeting and fantastical. But Elise Wright Knutsen, an atmospheric physicist at the University of Oslo, has gotten used to them.
“I’m Norwegian, so the aurora is a big thing here,” she said. “You kind of grow up with it happening over your head.”
But catching her first glimpse of the aurora on another planet hit differently.
“I cried a little bit,” she said.
Mars is known to have auroras — a glow normally produced when energetic particles from the sun strike a planet’s atmosphere. But they had been observed only by orbiting spacecraft, and only in ultraviolet — a light wavelength invisible to the naked eye. But with the help of precise space weather forecasting, NASA’s Perseverance rover and some persistence by a team led by Dr. Knutsen, a visible green aurora was spotted on the Red Planet for the very first time, dancing last March above ocher mountains.
As reported in a study published Wednesday in the journal Science Advances, a violent outburst from the sun on March 15, 2024, was forecast to crash into Mars just three days later. By commanding Perseverance to look up at just the right time, an explosion of green speckles was recorded on the rover’s cameras.
Scientists expected such an aurora, which was long thought to exist, to be spotted by spacecraft studying the Martian atmosphere. “I didn’t really expect it to be seen by one of the rovers,” said James O’Donoghue, a planetary astronomer at the University of Reading in England who was not involved with the new study.
As auroras are the expression of a planet’s atmosphere reacting to space weather, this discovery unlocks a new way to study the physics and chemistry of the Martian skies. It also showcases the ability of scientists to track the evolution of solar storms, which can be dangerous (and even lethal) to spacecraft and astronauts.
But for now, the team is mostly thrilled with having finally found Mars’s elusive, visible aurora. “It was so satisfying,” Dr. Knutsen said.
Auroras can be spied on worlds and moons throughout the solar system. Although some appear as visible light, most glimmer in either ultraviolet or infrared. The same can be said of Mars’s own ultraviolet aurora.
Dr. Knutsen suspected that a visible green aurora, not unlike Earth’s own, could also be seen on Mars. After all, the requisite atomic oxygen in the atmosphere was present — and when energetic particles from the sun slammed into that oxygen, a green glow should be expected to appear.
Luckily, Dr. Knutsen is also part of the Perseverance team. That rover’s primary mission is to look down at, and sample, rocks that may have signs of ancient microbial life. But she wondered if the robot’s cameras could also glance skyward and see an aurora.
One camera, Mastcam-Z, could spot any suspiciously green lights. But with the Martian atmosphere being materially different from Earth’s, several sky-high phenomena can create a jade-like glow. That’s where another of Perseverance’s eyes, SuperCam, would come into play: The instrument can identify the chemistry of whatever it is viewing, including that of any auroral luminescence.
Dr. Knutsen’s plan was to wait for a solar eruption, use forecasting models to see if, and when, it was going to hit Mars, and command Perseverance to gaze up. Her team began their quest in May 2023 and, after several failed attempts, finally struck green gold in 2024, a year in which the sun was particularly hyperactive.
On March 15, the sun unleashed a potent coronal mass ejection, a buckshot of charged particles that was forecast to hit Mars on March 18. Sure enough, the rover’s cameras recorded a shower of green particles made from energized atomic oxygen.
Dr. Knutsen, upon looking at the data files downloaded from Perseverance, quickly realized she was one of the first people to see a visible aurora on Mars: “a black horizon and a softly glowing green sky,” she said, describing the painterly view.
“It was on my birthday of all things,” Dr. Knutsen added. “It was a great day.”
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