The sun unleashed a flurry of radiation-filled explosions in May. When they crashed into Earth’s magnetic bubble, the world was treated to iridescent displays of the northern and southern lights. But our planet was not the only one in the line of solar fire.
A few days after Earth’s light appeared, another series of explosions screamed from the sun. This time, on May 20, Mars was hit by a beast of a storm.
Observed from Mars, “this was the strongest solar energetic particle event we’ve seen to date,” said Shannon Curry, principal investigator of NASA’s Mars Atmosphere and Volatile Evolution, or MAVEN, orbiter at the University of California, Berkeley.
When the burst arrived, it set off an aurora that enveloped Mars from pole to pole in a shimmering glow. If they stayed on the surface of Mars, “astronauts could see these auroras,” said Dr. Curry. Based on scientific knowledge of atmospheric chemistry, she and other scientists say, observers on Mars would have seen a green light show, even though no color cameras captured it on the surface.
But it is very lucky that there were no astronauts there. Mars’ thin atmosphere and lack of a global magnetic shield meant that its surface, as recorded by NASA’s Curiosity rover, was showered with a radiation dose equivalent to 30 chest X-rays – not a lethal dose, but certainly not pleasant to the human condition. .
While last month’s auroras were fascinating, they served as a reminder that Mars can be a dangerous, radiation-choked place, and that future astronaut visitors will need to be careful. “These solar storms pack a punch,” said Dr. Curry.
Lava tubes—long caverns created by volcanic activity—could offer Martian travelers strong shelter from solar storms. But with harmful solar particles sometimes reaching Mars within minutes, Earthlings will have to be light on their feet.
In other words, if you’re a Martian astronaut, “you better keep your space weather forecasts up to date,” said James O’Donoghue, a planetary astronomer at the University of Reading in England.
When the May 20 mega-explosion appeared, it was immediately seen to be terrifying. A powerful solar flare reached Mars first, showering it with X-rays and gamma rays. Hot on its heels was a powerful coronal mass ejection—a cluster of charged particles from the sun. “They seemed very fast to me,” said Mathew Owens, a space physicist at the University of Reading.
When particles from a solar salvo reach humanity’s home, they are caught in the Earth’s magnetic field and fall to the north and south magnetic poles. There, they bounce off various gas molecules in the atmosphere, temporarily energizing them and releasing countless bursts of visible color.
Mars lost its magnetic field centuries ago when its iron-rich core ceased to tempt, so May’s solar bombardment did not stop. “There’s nothing to stop these particles from going straight into the atmosphere,” said Nick Schneider, principal scientist working on the MAVEN Ultraviolet Imaging Spectrograph at the University of Colorado, Boulder.
Undergoing a global shock, auroras flared up across the planet. The MAVEN orbiter documented a thunderous ultraviolet glow, while a light green tint would be visible on the surface as it rose from the atmosphere’s turbulent oxygen atoms.
Some of the robotic inhabitants of Mars encountered the most unpleasant effects of the storm. The charged particles hit Curiosity’s navigation cameras and the star tracking cameras for the Mars Odyssey and Mars Reconnaissance Orbiter satellites, flooding them all with “snow”-like static.
Solar storms can also degrade a spacecraft’s solar panels. The May Whirlwind was no exception. “Everybody’s solar panels were hit,” said Dr. Curry. She added that a solar storm like the one on May 20 “causes about the same amount of degradation that we typically see in a year.”
None of the spacecraft were deeply damaged—and the scientific data they recorded has been warmly received. But these orbits may not always emerge unscathed from the sun’s fury. “The science team is excited every time we see these events,” said Dr. Curry. “Spacecraft operations team, less so.”
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