August 21, 2006—Spring on Mars comes in like a lion, according to a new theory.

Geysers formed by warming temperatures spew dust and ice hundreds of feet into Mars's air, scientists write in the latest edition of the journal Nature.

An artist's conception shows the violent thawing, which takes place near the planet's south pole (satellite map of Mars).

Mars's polar ice caps expand each winter as carbon dioxide in the planet's atmosphere freezes, the researchers say. But during spring, warmer weather slowly melts the expanded ice.

Some of this ice becomes translucent, allowing sunlight to heat carbon dioxide below the surface, changing it from a solid directly into a gas in a process called sublimation.

Eventually, the pressure from the gas becomes great enough that it penetrates the surface layer of ice in a violent eruption.

"These processes are unlike any observed on Earth," the researchers write.

The scientists say the theory may explain a long-standing mystery: strange dark spots, fanlike structures, and spidery patterns that appear near Mars's southern pole every year.

The dark spots and fans are dust thrown up by the geysers, while the spiders are the actual eruption sites, the scientists write.

The team proposed the theory after studying data from the Thermal Emission Imaging System on the Mars Odyssey orbiter.

—Aalok Mehta

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