Ancient Mars’ weather report: Continued cold and dry

Landscape features rule out warm or wet scenarios

HOT AND COLD Mars had a chilly youth, new research suggests, with much of the planet’s water locked away in high-altitude glaciers, as pictured in this artist’s illustration (right), though the ice was less extensive than shown here. Geologic evidence on the planet doesn’t match up with previous proposals of a warm, wet world (left).

R. Wordsworth

By Thomas Sumner

December 15, 2015 at 6:13 pm

SAN FRANCISCO — Visions of the ancient Red Planet as a warm, wet paradise are misplaced, new research suggests. Studying the Martian landscape, Harvard University planetary scientist Robin Wordsworth reasoned that the planet was generally a cold and dry place 3.8 billion to 3.5 billion years ago.

Clues about Mars’s past climate scar the landscape. Water, whether frozen or liquid, carves telltale features. If the planet had a cold and wet past, extensive glaciers would have whittled away the surface in the Martian highlands, but there’s no evidence for such colossal ice, Wordsworth found. Warm and wet doesn’t fit either — if now-cold Mars had once been wet enough to host oceans of water, that water should have built up titanic glaciers and left their mark as the planet chilled.

And a warm and dry past doesn’t explain signs of once-heavy snowfall in the Martian valley that engraved drainage channels in the ground. So by process of elimination, only a relatively dry and relatively cold Mars fits the bill, Wordsworth proposed December 14 at the American Geophysical Union’s fall meeting.

Those conditions weren’t extreme enough to preclude life, however. Microbes could have flourished during occasional warm periods, Wordsworth said.