Just before mid-September, 2017, an event on the sun caused a coronal mass ejection, sending charged solar particles hurtling into space, toward Mars. When the charged particles arrived at Mars on September 12 and 13, they sparked a global aurora more than 25 times brighter than any previously seen by the MAVEN orbiter, which has been studying the martian atmosphere’s interaction with the solar wind since 2014. Sonal Jain at CU Boulder (@jain_sonal on Twitter) is a member of MAVEN’s Imaging Ultraviolet Spectrograph instrument team. He commented in a statement:
When a solar storm hits the martian atmosphere, it can trigger auroras that light up the whole planet in ultraviolet light. The recent one lit up Mars like a light bulb.
An aurora on Mars can envelope the entire planet because Mars has no strong magnetic field like Earth’s to concentrate the aurora near polar regions.
Other Mars missions also observed the event, including the Curiosity rover on Mars’ surface. Its Radiation Assessment Detector, or RAD, measured radiation levels at the surface more than double any it had measured since landing in 2012. The high readings lasted more than two days. RAD Principal Investigator Don Hassler said:
This is exactly the type of event both missions were designed to study, and it’s the biggest we’ve seen on the surface so far.
NASA said observations like these aid both the planning for safety of future astronauts on Mars as well as in understanding of drastic environmental change that likely occurred on Mars, early in its history.
As long as we’re on Earth, events such as these don’t affect our human bodies (although they do have the potential to affect human technologies, such as electric grids and satellites in orbit). That’s because our thick atmosphere protects us.
But Mars’ atmosphere is much thinner than Earth’s, and so, on Mars, things are different. There, increased radiation from the sun can interact with the atmosphere to produce additional, secondary particles with the potential to harm unshielded human explorers. Hassler said:
If you were outdoors on a Mars walk and learned that an event like this was imminent, you would definitely want to take shelter, just as you would if you were on a space walk outside the International Space Station. To protect our astronauts on Mars in the future, we need to continue to provide this type of space weather monitoring there.
Besides the observations by instruments on MAVEN and Curiosity, effects of the September solar event were also detected by instruments on NASA’s Mars Odyssey orbiter and Mars Reconnaissance Orbiter and by the European Space Agency’s Mars Express orbiter.
The September, 2017 solar event that affected Mars took place as part of a spate of solar activity, seen from both Earth and Mars on opposite sides of the sun, last month. The activity was unexpected because we’re now heading toward solar minimum, a time of least activity in the sun’s 11-year sunspot and storm-activity cycle. Jain commented:
The current solar cycle has been an odd one, with less activity than usual during the peak, and now we have this large event as we’re approaching solar minimum.
During the specific event that caused global auroras on Mars, Earth – now on the opposite side of the sun from Mars – was not affected. However, we on Earth had our own unique brand of effects from solar activity in the form of auroras, like the one in the image above, in early September, 2017.
Bottom line: A September 2017 event on the sun sparked a global aurora on Mars, stronger than any seen before.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.