Solar storms may affect weather on Mars when they strike at the same time as major Martian dust storms, a new study has suggested for the first time.
Researchers found evidence of rising temperatures in the Red Planet's lower atmosphere when the two events coincided with each other – hinting that Mars may have a more complex atmospheric environment and weather system than previously thought.
The findings are being presented this week at the Royal Astronomical Society's National Astronomy Meeting in Birmingham .
A team of astronomers from Lancaster University, the University of Leicester and the Instituto de Astrofisica de Andalucia-CSIC in Granada, Spain, examined five solar energetic particle (SEP) events at Mars to find out whether long-lasting SEP events could warm Mars' lower atmosphere, where its weather happens.
Four of the SEP events showed no clear effect, but the fifth – which occurred in June 2018 – unexpectedly coincided with an expanding global dust storm that also wiped out NASA's Opportunity rover . It was during this event that signs of lower atmospheric heating were detected.
Lana Williams, a PhD researcher at Lancaster University who led the study, said: "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.
"The one exception occurred while a global dust storm was expanding across the planet."
The study used data from NASA's Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft and the European Space Agency's Trace Gas Orbiter. MAVEN studies the interaction between the Sun and Mars' upper atmosphere, while the Trace Gas Orbiter measures the composition and structure of the Martian atmosphere.
Observations were compared with expected temperature profiles from the Mars Climate Database. They examined temperatures before, during and after the five long-lasting SEP events.
The team cautions that a single observation is not enough to prove cause and effect. However, the finding raises the possibility that space weather and Martian dust storms might combine to affect the Red Planet's lower atmosphere in ways that have not previously been studied.
Solar energetic particle events occur when solar flares and coronal mass ejections (CMEs) release high-energy charged particles into space. Mars is particularly exposed to these particles because it has a thin atmosphere and no strong global magnetic field to shield the planet, as Earth does.
Previous research has shown that SEPs can affect Mars' upper atmosphere, causing ionisation, diffuse aurorae and disruption to radio signals. But their possible effects on the lower atmosphere, where weather processes take place, are not well understood.
Dust storms naturally heat parts of the Martian atmosphere by absorbing sunlight. However, the researchers found that the pattern of heating observed during the combined event was unusual for a dust storm and could not be explained by the storm alone.
The team had not initially set out to study dust storms. They identified the global storm only after noticing that heating appeared during only one of the observed SEP events, but not the others, and set out to investigate why.
Williams said: "Dust storms were not originally part of our investigation, so finding one happening at the same time as the heating was unexpected. It suggests that Mars' atmosphere and weather may respond to several events acting together, rather than each source of heating operating independently."
The astronomers stress that the result remains tentative. Further observations of SEP events occurring during Martian dust storms will be needed to determine whether the combination consistently produces unusual heating or whether another unobserved factor was involved.
As far as the team is aware, the possible interaction between SEPs, dust storms and lower-atmospheric heating has not previously been investigated.
The findings suggest that Mars has a more complex atmospheric environment and weather system than studies of solar activity or dust storms in isolation may reveal.
Understanding these combined effects could improve models of the Martian atmosphere and help researchers interpret future temperature observations during periods of intense solar and dust-storm activity.
