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Dry Ice Storms May Pelt Martian Poles, Experts Say

Erica Lloyd
for National Geographic News
December 19, 2005
 
Bombarded by violent storms of dry ice, the red planet's ice caps may have fewer silent nights than generally thought, according to new weather models.

Climate experts have long agreed that all is calm during the polar nights—the sunless winter months on Mars's north and south poles.

The poles are too cold, and the carbon dioxide rich atmosphere too thin and clear, to result in exciting weather, or so the thinking goes.

But now there's mounting evidence that temperature differences in the polar night stir up the atmosphere, creating storms.

"There's a lot of energy being released," said Timothy Titus, space scientist with the U.S. Geological Survey (USGS) in Flagstaff, Arizona.

At a meeting of the American Geophysical Union in San Francisco earlier this month, scientists even proposed that "thunderheads" form over Mars's southern polar cap.

Although it's not clear that a resulting storm would be electrical, some scientists believe it would release drafts akin to what Oklahomans might witness during a prairie thunderclap.

It would "tear apart" an airplane trying to fly through the system, said Anthony Colaprete, a space scientist at NASA's Ames Research Center in Moffett Field, California.

Alien Weather

Colaprete calls these proposed tempests thunderstorms, for lack of a better term. But he notes that, unlike Earth thunderstorms, these Martian polar storms in his models don't harbor water. Clouds instead are filled with carbon dioxide crystals, commonly known as dry ice.

Working with colleagues from NASA, Oregon State University, and the Southwest Research Institute in Boulder, Colorado, Colaprete developed 3-D models suggesting that such storms exist.

He believes the typical Martian polar storm cloud develops and disperses quickly, in perhaps an hour and a half.

Other scientists say they've observed what they believe may be similar storms lasting up to five hours.

Few experts, however, would recommend hanging around inside a Martian storm to find out how long it lasts.

If a temperature of -198°F (-128°C)—or colder—isn't bad enough, try keeping your balance in 30-mile-an-hour (48-kilometer-an-hour) downdrafts and spiraling winds while being pelted by buckets of salt-grain-size granules of dry ice.

"This weather is alien not only to Earth but to the entire solar system," Colaprete said.

Rumbling "Thunder"

Researchers suggest that a strange "thunder" rumbles in the Martian polar sky, resulting from carbon dioxide freezing and crackling.

On Mars "the higher-frequency sound waves don't travel very well, so you wouldn't really hear the high-pitched crackling," Colaprete said. "It would be more of a muffled crackle."

The space scientist has observed sound waves forming in his 3-D models. He can't confirm the thunder exists, though, until spacecraft measure such sounds on or above the Martian poles. No such mission is planned as of yet—Colaprete's findings are still very new.

As for lightning, scientists don't normally associate it with dry ice clouds. The carbon dioxide that makes up dry ice is simply not as prone to transmitting an electric charge as water.

But Colaprete isn't ruling out the possibility of dry ice-induced lightning yet. He notes that it's not clear that observers could even see the potential lightning flashes. That's because a thick haze known as the polar hood hovers over the Martian ice caps.

"The polar caps on Mars drive the climate on Mars much in the same way the oceans drive the climate on Earth, " the USGS's Titus said. So it's no surprise that researchers have been monitoring the caps in earnest.

In 1998 the Mars Global Surveyor orbiter began sending back unexpected data from the red planet's south pole.

Global Surveyor's laser altimeter, which mapped surface and atmospheric features, was firing pulses at the southern cap in winter and intercepting unexpectedly dense bodies in the atmosphere.

The peculiar masses hovered between 0.6 mile (1 kilometer) and 3.7 miles (6 kilometers) above ground.

Colaprete's modeling and other measurements convinced other scientists that these bodies were quickly forming "thunderheads."

Some experts, though, remain skeptical.

Greg Neumann is a geophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "I think [the bodies] are snowflakes or even hailstones," he said.

Violent "thunderheads" may or may not shake the polar night, Neumann added.

The red planet's weather is more complex than previously believed, though, Neumann said, citing data from the Global Surveyor project and other missions.

"The atmosphere of Mars is as diverse—or more so—as the Earth's."

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