for National Geographic News
Temperatures on Mars have increased slightly over a 20-year period due to the action of Martian winds, scientists have found.
New research has shown that dusty tornadoes called dust devils and gusty winds have helped the surface of Mars become darker, allowing it to absorb more of the sun's rays.
Lori Fenton at the NASA Ames Research Center in Moffett Field, California, and colleagues used a computer model to study the effect that winds have had on Mars's climate.
During the 1970s Mars experienced several large wind storms that stirred up bright, shiny dust particles and redistributed them around the planet, the team explained.
In the 1980s and 1990s smaller-scale processes like dust devils tidied up the planet, the researchers said, pushing the bright dust aside to expose the darker rocks below.
(See pictures of Mars.)
This process has decreased the planet's albedo, its ability to reflect solar radiation.
The team's results, published in this week's issue of the journal Nature, show that the decrease in Mars's reflectivity has caused a warming of 1.17 degree Fahrenheit (0.65 degree Celsius) between 1975 and 1995.
(Read related story: "Mars Melt Hints at Solar, Not Human, Cause for Warming, Scientist Says" [February 28, 2007].)
The study also predicted that Mars will continue to warm, due in part to a cycle caused by the planet's darkening surface.
"The darkened surfaces warm up, heating up the air just above the surface. This encourages formation of dust devils, which sweep up dust and [further] darken the surface," Fenton explained.
In addition, she said, the temperature difference between Mars's light and dark areas may cause an increase in gusty winds, which further perpetuates the cycle.
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