Something Really Weird Is Happening On Mars At Night - no bs

A satellite in orbit around Mars goes blind. Its star camera sees nothing for almost an hour. On the ground, a rover's photographs come back speckled with white, like snow on an old television. Its detector counts the equivalent of 30 chest X-rays taken in one go. And for a week, the whole night side of Mars glows green. But Mars doesn't have a magnetic field at all, does it? Three weeks before any of that happened, on the 29th of April 2024, the woman in charge of NASA's MAVEN orbiter said something out loud that most scientists keep to themselves. Shannon Curry said, in a NASA release, that she would love to see the big one hit Mars that year. A large solar event they could study before astronauts ever go. The Sun was near the top of its 11-year cycle. Mars was at its closest point to the Sun, in its dustiest season. Every instrument at the planet had been warned to watch. On the 20th of May, she got what she asked for. A flare erupted on the Sun that was later graded X-12, the strongest class there is based on data from the Solar Orbiter spacecraft. The X-rays and gamma rays hit Mars at the speed of light. The charged particles, the heavy stuff, arrived within tens of minutes. In Gale Crater, the Curiosity rover was in the middle of recording a wind gust with its navigation cameras. That is why the frames came back full of white streaks and specks. Those are not dust. They are particles from the sun striking the camera's detector. One flash per hit. The detector was not damaged. But right next to those cameras sits an instrument called RAD, a radiation counter that has been running since the rover landed in 2012. On an ordinary day it reads about 700 micrograys. On the 20th of May, 2024, it read 8,100, 8,130 chest X-rays delivered in one dose to anyone standing beside the rover. In orbit, the 2001 Mars Odyssey spacecraft, the oldest working machine at Mars, lost its star camera, the camera it uses to work out which way it is pointing. It came back within an hour. Odyssey had been here before. In 2003, a flare later rated X-45 destroyed its radiation detector outright. Two European orbiters, Mars Express and the Trace Gas Orbiter, both threw computer errors from the particles and recovered. The Trace Gas Orbiter's own dose counter recorded the equivalent of 200 normal days of radiation in 64 hours. And by pure luck, the two European craft were running a joint radio experiment that week, One beaming a signal through Mars' upper air to the other. They only do it twice a week. This time it ran 10 minutes after a flare struck. The number of electrons in one layer of the upper atmosphere jumped by 45%. In the layer above it, by 278%. Jacob Parrott, who led that study, called it the biggest response to a solar storm ever seen at Mars. And above it all, from the 14th to the 20th of May, MAVEN's ultraviolet camera watched aurora spread across the entire night side of the planet. Christina Lee, the mission's space weather lead, called it the largest solar particle event MAVEN had ever seen. So why did the whole night side light up, when on Earth a storm like this only lights up the poles? Because of what Mars doesn't have. On Earth, the aurora is a funnel. The planet's magnetic field catches particles from the Sun and pours them down over the poles, which is why you see the lights in Norway and not in Nairobi. Mars had a field like that once. The molten core that generated it shut down somewhere around 4 billion years ago, and the funnel went with it. So when a burst of solar particles arrives at Mars, nothing steers it. It rains straight into the upper atmosphere everywhere at once, and the whole night side glows. call that a diffuse aurora, and MAVEN had seen it before. In September 2017, during a storm, its camera measured aurora more than 25 times brighter than anything it had recorded up to then, and it covered every part of the nightside the camera could see. The same missing field is why the air is thin. MAVEN's job since 2014 has been to measure how fast the solar wind strips gas off the top of the atmosphere. On a quiet day, the answer is about 100 grams every second when a storm hit on the 8th of March 2015 the loss rate jumped to 10 to 20 times normal run that back over billions of years of a younger angrier sun and you get the desert we see now there is a version of that story with water in it too one reason NASA wanted the storm during the dusty season is a theory that a global dust storm and a solar storm together can lift water vapor high enough for the sun to strip it which would be how a wet planet became this one that is why the two machines matter together. Maven's instruments are tuned to the lower energy particles up top. Rad, on the ground, is the only instrument at Mars that sees the high energy ones that punch all the way through the atmosphere to where a person would stand. Don Hassler, who runs Rad, puts the difference simply. You can have a million particles with low energy or ten with extremely high energy it is the 10 that matter to a body and it is why he gave the advice he gave after May 2024 cliff sides or lava tubes would provide shielding for an astronaut from such an event in Mars orbit or deep space he said the dose would be significantly more that is the version everyone repeats no field so no shield so no air so sleep in a cave it is the version i would have given you before the storm's data came back, it is also only half true. And the half that is wrong is the half that makes the nights on Mars strange. The first crack in the story came from the surface and it was green. Elise Knudsen is a researcher at the University of Oslo and in 2023 she set out to do something nobody had done, photograph an aurora from the ground on another planet. Every Mars aurora up to then had been seen from orbit in ultraviolet a color no eye can register she wanted the color a person would see the problem is a rover cannot wait around at night with its cameras open every observation has to be planned three days ahead so her team watched the sun instead when a coronal mass ejection launched they judged its speed and the strength of the disturbance it would push ahead of it because in her words the faster the ejection the more likely it is to accelerate particles towards Mars and the stronger the disturbance around Mars the more likely those particles make it into the night side air between 2023 and 2024 they tried eight times the first three attempts found nothing then on the 15th of March 2024 a flare and a big ejection left the sun Christina Lee's team at Berkeley put out a Mars space weather alert NASA's modeling office ran the cloud forward and gave a time of arrival. Perseverance, in Jezero Crater, pointed its SuperCam spectrometer and its Mastcam-Z camera low over the horizon to look through the thickest slice of atmosphere it could. On the night of the 18th of March, the spectrometer picked out one exact line of light, 557.7 nanometers. That is the green of Earth's northern lights made by the same oxygen atoms. The sky over Jezero was faintly, measurably, green. Two months later, on the 18th of May, in the middle of the big storm, they caught it again, at about half the brightness, through a dustier sky. The last three attempts, with ejections that looked just as promising, found nothing. Roger Wiens, who runs SuperCam, was plain about what a person would have seen, the dull or dim green glow. The rover's instruments, he said, are not tremendously more sensitive than human eyes. So that is what the night side of Mars looks like in a storm to a human, a faint green haze over the whole sky. But when the maps of where the aurora appears came down from orbit, they did not show an even wash. They showed hotspots. And the hotspots were in the same place every time. In December 2014 and May 2020, MAVEN's ultraviolet camera swept the night side of Mars 33,319 times. In 278 of those sweeps, it found a small, sharp patch of aurora, the kind that does not come from a storm at all. Nearly all of them sat inside one rectangle in the southern highlands, 30 to 60 degrees south, 150 to 210 degrees east. Inside that box, the camera found an aurora on about 4% of its passes. Everywhere else, less than 1%. That rectangle is not random. It is the most magnetic ground on the planet. When Mars still had its core dynamo 4 billion years ago, lava was pouring out and cooling in the southern highlands. And as it hardened, the iron in it locked in the direction of the field it cooled in. The dynamo died. The rock kept the field. Today those fossil magnets read hundreds of nanotesla at the surface, and their field lines reach thousands of kilometers up into space. Each one is a small, private magnetosphere, a bubble of magnetism sitting on a planet that officially has none. And where the solar wind's own magnetic field meets the top of one of those bubbles pointing the opposite way, the two snap and reconnect, and electrons are fired down the field line into the air that is the same process that drives the aurora at Earth here it happens over a patch of old lava the size of a country and it does not need a storm it runs on an ordinary solar wind on an ordinary night and it is picky. A study published in 2025 matching the Hope orbiter's aurora images against MAVEN's readings of the solar wind found that the chance of an aurora over a given patch changes by up to a factor of seven depending on which way the sun's magnetic field happens to be pointing when it arrives, even the direction a patch faces matters some fossil magnets connect to the sky after dusk, others only in the hours before dawn, each one has its own schedule, so a planet with no magnetic field has hundreds of small ones. The question nobody could answer was what those small fields were actually doing up there, and whether they were a bare echo of Earth's system or a working copy of it. In July of this year, the answer landed, and it came from a spacecraft that was already dead. On the 6th of December 2025, MAVEN passed behind Mars on a normal orbit, the way it had thousands of times. When it came out the other side, nothing When engineers finally got a look at it, the spacecraft was spinning far faster than it should have been, and the spin had drained its batteries. Every attempt to reach it failed. On the 3rd of June 2026, NASA declared the mission over, after more than 11 years at Mars for a craft built to last one. But its data was still on the ground, and on the 23rd of July 2026, Shao Sui Shu at Berkeley and her colleagues published what one old pass had been hiding. On the 25th of February 2017, between 22:17 and 22:22 Universal Time, MAVEN had flown across the dusk line of Mars, straight over the strongest crustal fields in the South. In those five minutes, its three instruments, the magnetometer, the electron analyzer and the ion detector, had recorded every stage of the machine at once. field lines reconnecting, electric currents running along them, electrons being accelerated down toward the atmosphere, the upper air flowing in response, and the glow that follows. On Earth, physicists call that sequence the Dungey Cycle. It is the engine behind the Northern Lights, and it has been the standard picture of how a magnetic planet works with the Sun since the 1960s. Mars was running the same cycle, just smaller at Earth, the loop takes about an hour to go round. At Mars it takes about a minute, at Earth the voltage driving it is tens of thousands of volts at Mars roughly 50. Earth's version is about 20 times bigger in space but the parts are the same parts in the same order Shu's own words were that the team knew reconnection was happening at Mars but did not expect it to be like the Dungey cycle I think that sentence is the whole story it means the line in every textbook that Mars has no magnetic field is the wrong sentence Mars has no global field what it has instead is a scatter of fossil ones each running its own miniature aurora each rebuilding itself once a minute a magnetically haunted planet and the crust is not the only thing making the nightside glow some of the green has nothing to do with the sun's storms at all in 2020 the Trace Gas Orbiter had spotted Mars glowing green in daylight in 2023 its NOMAD instrument caught the same thing at night this is not aurora, no particle from the sun is hitting anything on the day side, sunlight breaks carbon dioxide apart and leaves loose oxygen atoms, winds carry those atoms high over the pole and into the dark, and there between 40 and 60 kilometers up they find each other, pair off into oxygen molecules and give back the energy as light, green light. Florian Soret, one of the authors describes it as the recombination of oxygen atoms created in the summer atmosphere and transported by winds made in summer on the day side delivered to winter in the dark, Mars Express had sniffed the same reaction in infrared a decade earlier but this was the first time anyone had caught it in color a person could see, Jean-Claude Gérard at Liège who led the study called the observations unexpected and interesting for future trips to the red planet, that is scientist for something bigger because this glow is bright, the team's estimate is that on a clear polar winter night it would look as bright as moonlit clouds on Earth enough for a person to see by enough for a rover to drive by and the sun does not have to do anything for it to be there so there are at least two greens over Mars the storm aurora faint and everywhere that Perseverance photographed and the night glow steady and polar that no storm made and then there is a third thing nobody has explained the United Arab Emirates Hope Orbiter has been photographing the whole night side of Mars in ultraviolet since 2021 nearly a thousand full images so far in about one image in 20 it sees something else long worm-like streaks of aurora stretching thousands of kilometers from the day side deep into the night far from any crustal field Rob Lillis at Berkeley who works on that camera called it a shocking discovery his team's position is that they have ideas but no solid explanation for an aurora of that shape at planetary scale now think about the person standing next to Curiosity on the 20th of May put a human in Gale Crater that day and this is what the record says happens 30 chest x-rays in one go at ground level under the thickest air Mars has in orbit worse the Trace Gas Orbiter took 200 days of radiation in 64 hours that is with a planet's worth of rock under you and a thin atmosphere above. It is why Hessler's answer was a cliff or a lava tube. But the same week gave that person something the textbooks did not, because the storm also showed that Mars is not a passive target. Its upper air answered the flare within 10 minutes, with electrons nearly quadrupling in one layer. Its fossil fields kept running their one-minute cycle underneath the wash of the storm, and the alert that told Perseverance where to point came from a person at Berkeley reading the sun three days out, the same way a coastal town reads a hurricane. That warning system is the thing that actually protects the first crew. For 11 years, part of it was MAVEN itself. When its instruments saw radiation climbing, the team sent word to the other spacecraft at Mars so they could protect their electronics before the worst of it arrived. In April 2024, before the storm, Shannon Curry admitted that for humans on the Martian surface, nobody had a solid handle on what radiation during solar activity actually does. By June 2026, the spacecraft that had been answering that question was gone, and the answer was still incomplete. But the system is about to get better. On the 13th of November 2025, two small spacecraft called Blue and Gold, the Escapade mission, from Florida. They arrive at Mars in September 2027 and start work in the spring of 2028. Two craft instead of one so that for the first time the solar wind can be measured coming in and the planet's answer measured at the same moment from two sides. Maven did that alone for 11 years and then fell silent. So here is where the question in the title actually lands. Something really is happening on Mars at night. And it is not one thing. It is a faint green aurora over the whole sky when the sun throws a storm. It is a brighter, steady green over the winter pole that the sun has nothing to do with. It is worm-shaped streaks that nobody can explain. And under all of it? A few hundred patches of 4 billion year old rock, running the same engine that lights up the poles of Earth, once a minute, on a planet that supposedly has no magnetic field at all. It has hundreds. The next one lands here. Subscribe.