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The sun fired off a volley of radiation-riddled outbursts in May. When they slammed into Earth\u2019s magnetic bubble, the world was treated to iridescent displays of the northern and southern lights. But our planet wasn\u2019t the only one in the solar firing line.<\/p>\n
A few days after Earth\u2019s light show, another series of eruptions screamed out of the sun. This time, on May 20, Mars was blitzed by a beast of a storm.<\/p>\n
Observed from Mars, \u201cthis was the strongest solar energetic particle event we\u2019ve seen to date,\u201d said Shannon Curry, the principal investigator of NASA\u2019s Mars Atmosphere and Volatile Evolution orbiter, or MAVEN, at the University of California, Berkeley.<\/p>\n<\/div>\n<\/div>\n
When the barrage arrived, it set off an aurora that enveloped Mars from pole to pole in a shimmering glow. If they were standing on the Martian surface, \u201castronauts could see these auroras,\u201d Dr. Curry said. Based on scientific knowledge of atmospheric chemistry, she and other scientists say, observers on Mars would have seen a jade-green light show, although no color cameras picked it up on the surface.<\/p>\n<\/div>\n<\/div>\n
But it\u2019s very fortunate that no astronauts were there. Mars\u2019s thin atmosphere and the absence of a global magnetic shield meant that its surface, as registered by NASA\u2019s Curiosity rover, was showered by a radiation dose equivalent to 30 chest X-rays \u2014 not a lethal dose, but certainly not pleasant to the human constitution.<\/p>\n
While last month\u2019s auroras were bewitching, they served as a reminder that Mars can be a dangerous, radiation-smothered place and that future astronaut visitors will have to beware. \u201cThese solar storms pack a punch,\u201d Dr. Curry said.<\/p>\n
Lava tubes \u2014 lengthy caves forged by volcanic activity \u2014 can provide Martian voyagers with hardy refuge from solar storms. But with the sun\u2019s deleterious particles sometimes reaching Mars in minutes, earthlings will have to be light on their feet.<\/p>\n
In other words, if you\u2019re a Martian astronaut, \u201cyou\u2019d better keep up to date on your space weather forecasts,\u201d said James O\u2019Donoghue, a planetary astronomer at the University of Reading in England.<\/p>\n<\/div>\n<\/div>\n
When the May 20 mega-eruption emerged, it was immediately obvious that it was formidable. A powerful solar flare reached Mars first, bathing it In X-rays and gamma rays. Hot on its heels was a potent coronal mass ejection \u2014 a buckshot of charged particles from the sun. \u201cThey looked pretty fast to me,\u201d said Mathew Owens, a space physicist at the University of Reading.<\/p>\n
When particles from a solar salvo reach humanity\u2019s home, they are caught in Earth\u2019s magnetic field and spiral down into the north and south magnetic poles. There, they bounce off different gas molecules in the atmosphere, temporarily energizing them and unleashing bursts of myriad, visible colors.<\/p>\n
Mars lost its magnetic field eons ago when its iron-rich innards stopped churning, so May\u2019s solar bombardment was not intercepted. \u201cThere\u2019s nothing to stop these particles plowing right into the atmosphere,\u201d said Nick Schneider, the lead scientist working on the Imaging Ultraviolet Spectrograph on MAVEN at the University of Colorado, Boulder.<\/p>\n
Subjected to a global pummeling, auroras ignited across the entire planet. The MAVEN orbiter documented a thunderous ultraviolet glow, while a light green hue would have been visible on the surface as it emanated from the atmosphere\u2019s agitated oxygen atoms.<\/p>\n<\/div>\n<\/div>\n
Some of Mars\u2019s robotic residents encountered the more unpleasant effects of the storm. Charged particles hit Curiosity\u2019s navigation cameras and the star tracker cameras for the Mars Odyssey and Mars Reconnaissance Orbiter satellites, inundating them all with static like \u201csnow.\u201d<\/p>\n
Solar storms can also degrade a spacecraft\u2019s solar panels. May\u2019s maelstrom was no exception. \u201cEverybody\u2019s solar panels took a hit,\u201d Dr. Curry said. She added that one solar storm like that of May 20 \u201ccauses about the same amount of degradation that we typically see over a year.\u201d<\/p>\n
None of the spacecraft were deeply damaged \u2014 and the scientific data they recorded has been warmly received. But these orbiters may not always emerge unscathed in the face of the sun\u2019s fury. \u201cThe science team is thrilled every time we see these events,\u201d Dr. Curry said. \u201cThe spacecraft ops team, less so.\u201d<\/p>\n<\/div>\n<\/div>\n