for National Geographic News
Mars has gone through 40 ice ages during the past five million years that regularly send the planet's permanent ice sheets cascading toward the equator, then melting backward, a new theory suggests.
The climate changes are likely driven by cyclical fluctuations in the planet's orbit that alter the amount of sunlight that falls on the planet's surface, says astronomer Norbert Schörghofer of the University of Hawaii at Manoa.
Understanding the sun's exact role in the Martian ice ages could help solve longstanding puzzles about the red planet.
It could also help scientists better understand Earth's complex climatic systems, which are also affected by orbital variations.
The new theory appears in this week's issue of the journal Nature.
Mystery of the Ice
In recent years extensive amounts of ice have been discovered below the surface of Mars. Much of the ice mysteriously survives far from the planet's poles. (Related photo: "'Frozen Sea' Seen on Mars [February 23, 2005].)
Schörghofer suggests that this ice is newer than previously believed.
"Earlier theories have tried to explain this ice with snowfall that would have happened some five million years ago [but struggle] to explain how that ice could have stayed there," Schörghofer said.
"I'm saying it didn't stay. It went away and then came back many, many times."
According to Schörghofer, much of Mars's ice is formed by vapor diffusion—the seeping of gas directly into underground pockets during cold periods.
"The water cycle on Mars is very different than what we see on Earth," said Joshua Bandfield, a research specialist at Arizona State University's School of Earth and Space Exploration who was not involved in the study.
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