The sun fired off a volley of radiation-riddled outbursts in May. When they slammed into 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 screamed out of the sun. This time, on May 20, Mars was blitzed 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, the principal investigator of NASA’s Mars Atmosphere and Volatile Evolution orbiter, or MAVEN, at the University of California, Berkeley.

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, “astronauts could see these auroras,” 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.

But it’s very fortunate that no astronauts were there. Mars’s thin atmosphere and the absence of a global magnetic shield meant that its surface, as registered by NASA’s Curiosity rover, was showered by a radiation dose equivalent to 30 chest X-rays — not a lethal dose, but certainly not pleasant to the human constitution.