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Moon and Mars

March 21, 2015

Modern-day Mars is cold and hostile. Dried-up riverbeds meander across the ancient Martian terrain, though, so rivers must have flowed across the planet billions of years ago. But that poses a bit of a puzzle, because Mars is half-again as far from the Sun’s light as Earth is. And when Mars was young, the Sun was much fainter than it is today. So how did Mars get warm enough for rivers to flow?

A new idea may answer the question: punctuated volcanism.

Artist's concept of Olympus Mons, largest volcano on MarsArtist's concept of Olympus Mons, the largest volcano on present-day Mars [NASA/MOLA team]Mars has plenty of volcanoes. In fact, its largest volcanoes dwarf any on Earth. And volcanic plains cover much of the Martian surface, indicating that Mars was volcanically active for much of its history.

According to the new idea, giant eruptions took place about 3.7 billion years ago, releasing huge amounts of sulfur dioxide gas into the atmosphere.

Like carbon dioxide, sulfur dioxide is a greenhouse gas, so it traps heat from the Sun. The new calculations indicate that after a major volcanic eruption, regions along the equator saw daily high temperatures above the freezing mark for a good part of the year — conditions that persisted for decades or even centuries. As a result, ice melted and rivers began to flow. After a while, the planet froze again — at least until the next big eruption.

Look for Mars close to the right of the crescent Moon shortly after sunset this evening. The little planet is a bit tough to see through the twilight, but binoculars can help you pick it out.


Script by Ken Croswell, Copyright 2015

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