Mars' Climate In Flux: Mid-latitude Glaciers

Conspicuous trains of debris in valleys, arcs of debris on steepslopes and other features far from the polar ice caps bear strikingsimilarities to glacial landscapes of Earth, says Brown University'sJames Head III. When combined with the latest climate models andorbital calculation for Mars, the geological features make a compellingcase for Mars having ongoing climate shifts that allow ice to leave thepoles and accumulate at lower latitudes.

"The exciting thing is a real convergence of these things,"said Head, who presented the latest Mars climate discoveries on Sunday,16 October, at the Annual Meeting of the Geological Society of Americain Salt Lake City.

"For decades people have been saying that deposits at mid andequatorial latitudes look like they are ice-created," said Head. Butwithout better images, elevation data and some way of explaining it,ice outside of Mars' polar regions was a hard sell.

Now high-resolution images from the Mars Odyssey spacecraft'sThermal Emission Imaging System combined with images from the MarsGlobal Surveyor spacecraft's Mars Orbiter Camera and Mars Orbiter LaserAltimeter can be compared directly with glacier features in mountainand polar regions of Earth. The likenesses are hard to ignore.

For instance, consider what Head calls "lineated valley fill."These are lines of debris on valley floors that run downhill andparallel to the valley walls, as if they mark some sort of past flow.The same sorts of lines of debris are seen in aerial images of Earthglaciers. The difference is that on Mars the water ice sublimes away(goes directly from solid ice to gas, without any liquid phase between)and leaves the debris lines intact. On Earth the lines of debris areusually washed away as a glacier melts.

The lines of debris on Mars continue down valleys and convergeswith other lines of debris - again, just like what's seen on Earthwhere glaciers converge.

"There's so much topography and the debris is so thick (onMars) that it's possible some of the ice might still be there," saidHead. The evidence for present day ice includes unusually degradedrecent impact craters in these areas - just what you'd expect to see ifa lot of the material ejected from the impact was ice that quicklysublimed away.

Another peculiarly glacier-like feature seen in Martianmid-latitudes are concentric arcs of debris breaking away from steepmountain alcoves - just as they do at the heads of glaciers on Earth.

As for how ice could reach Mars lower latitudes, orbitalcalculations indicate that Mars may slowly wobble on its spin axis farmore than Earth does (the Moon minimizes Earth's wobble). This meansthat as Mars' axis tilted to the extremes - up to 60 degrees from theplane of Mars' orbit - the Martian poles get a whole lot more sunshinein the summertime than they do now. That extra sun would likely sublimewater from the polar ice caps, explains Head.

"When you do that you are mobilizing a lot of ice andredistributing it to the equator," Head said. "The climate models aresaying it's possible."

It's pure chance that we happen to be exploring Mars when itsaxis is at a lesser, more Earth-like tilt. This has led to the falseimpression of Mars being a place that's geologically and climaticallydead. In fact, says Head, Mars is turning out to be a place that isconstantly changing.

Lineated Valley Fill at the Dichotomy Boundary on Mars: Evidence for Regional Mid-Latitude GlaciationView abstract:http://gsa.confex.com/gsa/2005AM/finalprogram/abstract_94125.htm