The sun fired off a salvo of radiation-strewn explosions in May. When they hit Earth’s magnetic bubble, the world was treated to iridescent displays of the northern and southern lights. But our planet wasn’t the only one in the solar firing line.
A few days after Earth’s light show, another series of eruptions erupted from the sun. This time, on May 20, Mars was hit by a storm.
Observed from Mars, “this was the most powerful solar energetic particle event we’ve seen to date,” said Shannon Curry, principal investigator for NASA’s Mars Atmosphere and Volatile Evolution orbiter, or MAVEN, at the University of Colorado, Boulder.
When the fire arrived, it launched an aurora that enveloped Mars from pole to pole in a glittering glow. If they were standing on the surface of Mars, “astronauts could see these auroras,” said Dr. Curry. Based on scientific knowledge of the chemistry of the atmosphere, she and other scientists say that observers on Mars would see a jade-green light show, even if no color cameras on the surface picked it up.
But it is very lucky that there were no astronauts. Mars’ thin atmosphere and absence of a global magnetic shield meant that its surface, as registered by NASA’s Curiosity rover, was showered with a dose of radiation equivalent to 30 chest X-rays – not a lethal dose, but certainly not pleasant to the human constitution. .
While last month’s auroras were mesmerizing, they served as a reminder that Mars can be a dangerous place shrouded in radiation, and that future astronaut visitors will need to be careful. “These solar storms are great,” said Dr. Curry.
Lava tubes—long caverns formed by volcanic activity—may provide Martian travelers with durable shelter from solar storms. But since harmful particles from the Sun sometimes reach Mars within minutes, Earthlings will have to be light on their feet.
In other words, if you’re a Martian astronaut, “you’d better have up-to-the-minute space weather forecasts,” said James O’Donoghue, a planetary astronomer at the University of Reading in England.
When the May 20 megaeruption appeared, it was immediately apparent that it was threatening. A powerful solar flare was the first to reach Mars, flooding it with X-rays and gamma rays. Hot on its heels was a massive coronal mass ejection—a shot of charged particles from the sun. “They looked pretty fast to me,” said Mathew Owens, a space physicist at the University of Reading.
When particles from a solar flare reach humanity’s home, they are caught in the Earth’s magnetic field and spiral down to the north and south magnetic poles. There, they bounce off various gas molecules in the atmosphere, temporarily energizing them and releasing flashes of myriad visible colors.
Mars lost its magnetic field eons ago when its iron-rich interior stopped swirling, leaving Mayo’s solar bombardment undetected. “There’s nothing stopping these particles from hurtling straight into the atmosphere,” said Nick Schneider, principal scientist working on MAVEN’s Imaging Ultraviolet Spectrograph at the University of Colorado, Boulder.
Auroras exposed to a global strike flared up across the planet. The MAVEN orbiter documented a burst of ultraviolet radiation, while a pale green hue was visible on the surface as it emanated from disturbed oxygen atoms in the atmosphere.
Some of the robotic inhabitants of Mars encountered more unpleasant consequences 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 static electricity like “snow”.
Solar storms can also degrade the spacecraft’s solar panels. Mayo’s vortex was no exception. “All the solar panels were hit,” said Dr. Curry. She added that a single 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 science data they recorded was warmly received. But these orbiters may not always emerge unscathed in the face of solar fury. “The scientific team is excited every time we see these events,” said Dr. Curry. “The spaceship operations team less so.