A global-scale dust storm could envelop the Red Planet within the next few months, according to planetary researchers at NASA’s Jet Propulsion Laboratory (JPL).
Two 2001 images from NASA’s Mars Global Surveyor orbiter show a dramatic change in the Red Planet’s appearance when haze raised by dust-storm activity in the south became globally distributed. At left, an image from late June 2001 shows clear conditions over much of Mars, with regional dust-storm activity occurring in the Hellas basin (bright oval feature) near the edge of the south polar cap. At right, a July 2001 image from the same perspective shows the planet almost completely enveloped. Dust extends to altitudes of more than 37 miles (60 km) during global-scale dust storms. Image credit: NASA / JPL / MSSS.
Local dust storms occur frequently on Mars. These localized storms occasionally grow or coalesce to form regional systems, particularly during the southern spring and summer, when Mars is closest to the Sun.
On rare occasions, regional storms produce a dust haze that encircles the planet and obscures surface features beneath.
“Global-scale dust storms on Mars represent the most spectacular form of atmospheric interannual variability observed on any of the terrestrial planets,” JPL scientists Dr. James Shirley and Dr. Michael Mischna explained in a paper posted online May 4, 2016 at the preprint site arXiv.org.
“During these events, atmospheric temperatures may locally exceed their seasonal norms by more than 40 degrees Kelvin (although at the surface, a moderation of diurnal temperature extremes is typically observed, due to the interception of incoming solar radiation and outgoing thermal radiation by atmospheric dust).”
“The atmosphere, thus warmed, expands significantly. Dust may extend to altitudes of more than 37 miles (60 km) above the surface, and the large-scale circulation is profoundly impacted.”
Mars has been observed shrouded by planet-encircling dust nine times since 1924, with the five most recent planetary storms detected in 1977, 1982, 1994, 2001 and 2007.
The actual number of such events is no doubt higher. In some of the years when no orbiter was observing Mars up close, the planet was poorly positioned for Earth-based telescopic detection of dust storms during the Martian season when global storms are most likely.
Dr. Shirley’s 2015 paper in the journal Icarus reported finding a pattern in the occurrence of global-scale dust storms when he factored in a variable linked to the orbital motion of Mars.
Other planets have an effect on the momentum of Mars as it orbits the Solar System’s center of gravity.
This effect on momentum varies with a cycle time of about 2.2 years, which is longer than the time it takes the Red Planet to complete each orbit: about 1.9 years. The relationship between these two cycles changes constantly.
Dr. Shirley found that global-scale dust storms tend to occur when the momentum is increasing during the first part of the dust storm season.
None of the global dust storms in the historic record occurred in years when the momentum was decreasing during the first part of the dust storm season.
The scientist noted that conditions in the current Mars dust-storm season are very similar to those for a number of years when global storms occurred in the past.
Observations of the Martian atmosphere over the next few months will test whether the forecast is correct.
“Mars will reach the midpoint of its current dust storm season on October 29th of this year,” Dr. Shirley said.
“Based on the historical pattern we found, we believe it is very likely that a global dust storm will begin within a few weeks or months of this date.”
Researchers at Malin Space Science Systems post Martian weather reports each week based on observations using the Mars Color Imager camera on NASA’s Mars Reconnaissance Orbiter. A series of local southern-hemisphere storms in late August grew into a major regional dust storm in early September, but subsided by mid-month without becoming global.
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James H. Shirley & Michael A. Mischna. 2016. Orbit-spin coupling and the interannual variability of global-scale dust storm occurrence on Mars. arXiv: 1605.01452
James H. Shirley. 2015. Solar System dynamics and global-scale dust storms on Mars. Icarus 251: 128-144; doi: 10.1016/j.icarus.2014.09.038
This article is based on a press-release issued by NASA.
