Dark Times Ahead for the Red Planet?
(From the September/October 2001 issue of StarDate magazine)
Dark months may lie ahead for Mars. A dust storm that whirled to life in mid-June and covered most of the planet a month later may pre-sage even bigger storms in the coming months, according to scientists who study the Martian climate. The storms may require engineers to modify plans for Mars Odyssey, a spacecraft scheduled to enter orbit around Mars on October 24, although the changes should not affect its mission.
Scientists first saw the dust storm on June 15 in the Hellas Basin, an impact crater in the southern hemisphere. On June 26 it started to grow rapidly. By early July the storm encircled almost the entire southern hemisphere, and days later it covered much of the northern hemisphere, too. It was still in full force later in the month.
Like the other large dust storms observed on Mars in the last three decades, this one began when the planet was near perihelion, its closest approach to the Sun. When a big storm appears near perihelion, similar storms often arise later on. This storm popped up even earlier in the season than those seen in the past, so scientists speculate that Mars may experience an unusually busy storm season over the next few months.
The storms lift so much dust into the air that they block much of the sunlight, turning the planet’s surface dark and gloomy. Winds may race at 60 to 100 miles per hour (95-160 kph).
Scientists hope the storms will help them understand how such maelstroms stir to life, why they last for many weeks or months, and how and why the dust eventually settles back to the surface. Current theories suggest the storms begin when some areas on the surface heat more quickly than others, warming the atmosphere above them. Warm air rushes toward colder air, creating strong winds that pick up the powdery soil.
Dust particles warm the atmosphere even more, helping the storm grow. An instrument aboard Mars Global Surveyor, which has orbited Mars since 1997, measured an overall temperature increase of about 54 degrees Fahrenheit (30 C) from June 15 to July 15.
The extra heat causes the atmosphere to expand, which may impact plans for Mars Odyssey. For 11 weeks after entering orbit, the craft occasionally will dip into the outer atmosphere to shape its final orbit. Changes in the atmosphere reported by Global Surveyor will help ground controllers refine these “aerobraking” maneuvers.
Once it reaches its final orbit next year, Odyssey will use three scientific instruments to help scientists understand the planet’s climate and geologic history. It also will provide information on Martian water and search for evidence of past life.
Odyssey is NASA’s first mission to Mars since the loss of Climate Orbiter and Polar Lander in 1999. The agency instituted several changes to improve Odyssey’s chances of survival, including a tracking technique that compares the spacecraft’s position to that of a quasar (a bright, remote object). The technique was devised to prevent a repeat of Climate Orbiter’s demise; the craft was destroyed when it dipped too low into the Martian atmosphere as it attempted to enter orbit. Engineers had not properly converted English to metric measurements, so the craft was slightly off course, and tracking systems did not discover the error until it was too late to correct.
Odyssey’s mission is scheduled to last until 2003, when it will serve as a communications relay station for American and European landers. — Damond Benningfield
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