It took seven months to confirm that NASA’s Opportunity rover was dead. The U.S. space agency’s little robotic probe had stopped communicating with Earth back on June 10, 2018—after being engulfed by a severe Martian dust storm then blanketing the entire Red Planet. It’s taken years, but physicists now have some idea about why exactly that storm became so dangerous.
New research presented this month at the Royal Astronomical Society’s National Astronomy Meeting has uncovered compelling evidence that radiation from solar storms is capable of magnifying weather events on Mars after penetrating the planet’s weak magnetosphere. The new study scrutinized data from NASA’s orbital MAVEN spacecraft and the European Space Agency’s Trace Gas Orbiter to determine just how much solar energetic particle (SEP) events heat up Mars’ lower atmosphere. The researchers’ results surprised them: When compared to expected global temperatures estimated from the Mars Climate Database, it looks like intense solar flares and other stellar radiation can act on Martian dust storms synergistically, increasing their severity and roiling Mars’ lower atmosphere.
“Dust storms were not originally part of our investigation, so finding one happening at the same time as the heating was unexpected,” Lancaster University physicist Lana Williams, who studies Martian space and atmospheric plasma dynamics, said in a statement. “It suggests that Mars’ atmosphere and weather may respond to several events acting together, rather than each source of heating operating independently,” according to Williams, who led the new study.
Kicking up a storm
Williams and her colleagues had originally intended to examine five SEP events to ascertain whether or not radiation from solar storms had any effect closer to the Martian surface, where actual weather patterns emerge. Past research had already documented cases where solar eruptions, like solar flares or coronal mass ejections, generated measurable effects in Mars’ upper atmosphere—including aurorae like Earth’s own Northern Lights and additional leakage of Mars’ atmospheric gases into space.
“We expected that these highly energetic particles might have some effect on temperatures in Mars’ lower atmosphere, but in four of the five events we studied we found no clear evidence of heating,” Williams said. “The one exception occurred while a global dust storm was expanding across the planet.”
During this June 2018 SEP event, ESA’s Trace Gas Orbiter recorded an increase of about 90 degrees Fahrenheit (50 degrees Celsius) at roughly 47 and 78 miles (75 and 125 kilometers) of altitude, as Williams told IFLScience. For context, Mars’ exobase, the altitude at which its gases start to bleed into space, begins around 87 miles (140 km) up and its most turbulent atmosphere, or homopause altitude, rests around 56 and 84 miles (90 and 135 km) high.
Clouded by uncertainty
Williams and her collaborators—astronomers at the UK’s University of Leicester and Spain’s Instituto de Astrofisica de Andalucia-CSIC in Granada—also found a July 2021 SEP event that appeared to produce a similar, albeit smaller, increase in Martian temperatures. But the team noted that these two episodes are far from enough corroborating evidence to confirm that this phenomenon is real.
“[A] clear heating effect is observed, but further research is required to attribute atmospheric temperature variations as a result of the global dust storms and SEP events where the two occur simultaneously,” the researchers stated in their new study.
One aspect obscuring the picture is the weaker signal from the July 2021 event, which only increased temperatures somewhere between one tenth and one fifth of what the June 2018 SEP blast accomplished. Nevertheless, Williams hopes further analysis of data taken by ESA’s Trace Gas Orbiter from 2022 to present might settle the issue.
She said she was particularly curious about a May 2024 solar storm so strong that NASA’s Curiosity rover captured evidence of the storm’s charged particles sailing toward the Martian surface on video.
“It is a case of we just don’t have the data at the minute to look further into it,” as Williams told IFLScience, “but it would be interesting to look at the 2024 solar storm.”
