Saturday, October 8, 2016

Martian Dust Storms May Follow Predictable Patterns

Two 2001 images from the Mars Orbiter Camera on NASA's Mars Global Surveyor orbiter show a dramatic change in the planet's appearance when haze raised by dust-storm activity in the south became globally distributed. The images were taken about a month apart. Credits: NASA/JPL-Caltech/MSSS

Global dust storms on Mars may follow a predictable pattern, with an active period likely to begin at the end of this month, according to NASA Jet Propulsion Laboratory (JPL) planetary scientist James Shirley. Last year, Shirley published a study in the journal Icarus in which he reported a predictable pattern to the occurrence of dust storms powerful enough to affect the entire planet.

Localized dust storms frequently occur on the Martian surface. Some of those grow into regional storms, especially during the southern hemisphere’s springs and summers, when Mars is closest to the Sun in its elliptical orbit.

Although the phenomenon is rare, regional dust storms can generate dust hazes that cover the whole planet, making surface features hard or impossible to be seen. These can escalate into global dust storms that can last for many Earth days and even weeks. The threat posed by global dust storms is a concern for both robotic missions to the Red Planet as well as for future astronauts living there.

In the book and movie The Martian, the winds of a dust storm were strong enough to threaten the lives of a group of astronauts and force them to abandon their habitat on the planet.

No dust storm on Mars is that strong, but the swirling dust they produce is capable of harming electronic devices, preventing solar-powered machines from receiving sunlight, and having detrimental effects on astronauts’ health.

Since 1924, scientists have observed nine global dust storms in which the entire planet was surrounded by dust, most recently in 1977, 1982, 1994, 2001, and 2007.

Additional global dust storms probably had occurred but were not observed due to an orbiter not being present to see them while Mars was in a difficult position to observe from Earth.

In 1971, the first spacecraft to orbit Mars, Mariner 9, arrived during a planet-wide dust storm.

More recently, in 2007, a global dust storm threatened to shut down the twin Mars Exploration Rovers Spirit and Opportunity, positioned on opposite sides of the planet, by blocking the sunlight needed to power them.

John Callas of JPL, project manager for Spirit and Opportunity, describes that storm as the “first major threat” to the rovers since their landing on the Red Planet in 2004.

“We had to take special measures to enable their survival for several weeks with little sunlight to keep them powered. Each rover powered up only a few minutes each day, enough to warm them up, then shut down to the next day without even communicating with Earth. For many days during the worst of the storm, the rovers were completely on their own,” Callas said.

In his paper, Shirley stated he found a pattern in the timing of global dust storms when he added Mars’ orbital motion to his calculations.

Mars orbits the Sun every 1.9 Earth years. However, as Mars orbits the Solar System’s center of gravity, its momentum is influenced by other planets in the Solar System, resulting in a varying momentum cycle lasting 2.2 Earth years. The relationship between Mars’ orbital period and this momentum cycle continually changes.

Global dust storms occur mainly when the planet’s momentum is increasing, during the dust storm season’s first half, Shirley found. Of the known global dust storms that have occurred on the Red Planet, all have happened during this time of increasing planetary momentum and none during periods of decreasing momentum.

Mars is currently in this first part of the dust storm season and is experiencing conditions very much like those that preceded previous global dust storms, Shirley warns.

“Mars will reach the midpoint of its current dust storm season on October 29th of this year. 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,” he said.

The San Diego-based Malin Space Science Systems website posts weekly Martian weather reports compiled from data collected by the Mars Reconnaissance Orbiter’s Mars Color Imager Camera.

Regular monitoring of Mars’ atmosphere over the next few months will indicate whether Shirley’s prediction is correct. While a group of local dust storms on Mars’ southern hemisphere in late August expanded into a regional storm the following month, the phenomenon has since subsided without becoming global.

Written by: Laurel Kornfeld
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