Some recent research suggests that early Mars was cold most of the time and warmed up only when objects impacted the planet. The impacts would warm the atmosphere and melt water trapped in underground and surface ice, causing rivers to flow and cutting the valleys that rival Arizona's Grand Canyon.
"I do not think this is right," said Dr. James F. Kasting, distinguished professor of geosciences and meteorology. "I do not think there was enough time involved to form the types of features that we see on the Martian landscape."
Kasting believes that a greenhouse effect warmed the planet. However, he has calculated that a carbon dioxide and water greenhouse would not have warmed the planet above the freezing point of water. On Mars, before enough carbon dioxide accumulated in the atmosphere to warm things up, the carbon dioxide would condense into dry ice clouds and eventually there would be ice caps.
"It does not seem possible to get above freezing with gaseous carbon dioxide and water," he told attendees at the annual meeting of the American Association for the Advancement of Science today (Feb. 14) in Denver.
Which is why some researchers think the planet was never warm. But, according to Kasting, features like Nanedi Vallis, which is a half-mile to over a mile wide in places and over a half mile deep, could not be made during the short time rivers would run after an impact.
"The channel at the bottom of Nanedi Vallis is only about 100 feet across," says Kasting. "It took millions of years of constant running water to carve the Grand Canyon. It would take a similar time on Mars."