NASA’s Mars orbiters have unveiled a pattern of large regional dust storms occurring at about the same times each year, an advance that may help predict these hazardous events during future robotic and human missions to the red planet.
After decades of research to discern seasonal patterns in Martian dust storms from images showing the dust, but the clearest pattern appears to be captured by measuring the temperature of the red planet’s atmosphere.
For six recent Martian years, temperature records from NASA Mars orbiters reveal a pattern of three types of large regional dust storms occurring in sequence at about the same times each year during the southern hemisphere spring and summer. Each Martian year lasts about two Earth years.
“When we look at the temperature structure instead of the visible dust, we finally see some regularity in the large dust storms,” said David Kass of NASA’s Jet Propulsion Laboratory in the US.
“Recognising a pattern in the occurrence of regional dust storms is a step toward understanding the fundamental atmospheric properties controlling them,” he said.
Dust lofted by Martian winds links directly to atmospheric temperature: The dust absorbs sunlight, so the Sun heats dusty air more than clear air.
In some cases, this can be dramatic, with a difference of more than 35 Celsius degrees between dusty air and clear air.
This heating also affects the global wind distribution, which can produce downward motion that warms the air outside the dust-heated regions.
Thus, temperature observations capture both direct and indirect effects of the dust storms on the atmosphere.
Improving the ability to predict large-scale, potentially hazardous dust storms on Mars would have safety benefits for planning robotic and human missions to the planet’s surface.
Also, by recognising patterns and categories of dust storms, researchers make progress toward understanding how seasonal local events affect global weather in a typical Mars year.
Researchers analysed temperature data representative of a broad layer centred about 25 kilometres above the Martian surface. That is high enough to be more affected by regional storms than by local storms.
Most Martian dust storms are localised, smaller than about 2,000 kilometres across and dissipating within a few days. Some become regional, affecting up to a third of the planet and persisting up to three weeks.
Three large regional storms, dubbed types A, B and C, all appeared in each of the six Martian years studied.
Multiple small storms form sequentially near Mars’ north pole in the northern autumn, similar to Earth’s cold-season Arctic storms across North America, researchers said.
The study was published in the journal Geophysical Research Letters.