Mars is coming out of an ice age, study shows

An analysis ofradar images that peered inside the polar ice caps of Mars showsthat Earth's neighbour is coming out of an ice age that is partof an ongoing cycle of climate change, scientists said onThursday.

The Martian ice began its retreat about 370,000 years ago,marking the end of the last ice age, according to theresearchpublished in the journal Science.

Scientists are keenly interested in piecing together theclimate history of Mars, which contains strong evidence thatoceans and lakes once pooled on its surface, bolstering theprospects for life.

Scientists can now use the new ice measurements in computersimulations to more accurately model the Martian climate, saidplanetary scientist Isaac Smith of the Southwest ResearchInstitute in Boulder, Colorado, who led the study.

"Previously those models were unconstrained by observationsso they started with guesses. Now they have more to run on,"Smith said.

The study also was the first to tie a specific layer ofMartian ice with a specific period of time. "Eventually we'dlike to be able to do this for every layer," Smith said.

Using images taken by satellites orbiting Mars, theresearchers determined that about 87,000cubic kilometres (20,872 cubic miles)of ice has accumulated at its poles since the end ofthe ice age, mostly in the northern polar cap.

Warm poles

Unlike Earth, ice ages on Mars occur when its poles arewarmer than average and frozen water is more stable at lowerlatitudes. Transitions between lengthy climate phases can leavetelltale features in the ice, the research showed.

For example, Smith and colleagues found dramatic slopes inlayers of ice within the Martian northern ice cap. Other layersreveal ice flowing in reverse direction. The climate cycles aretriggered by changes in Mars' orbit and tilt, which affect howmuch sunlight reaches the planet's surface.

The shifts are particularly dramatic on Mars because theplanet's tilt changes by as much as 60 degrees, compared to
variations in Earth's tilt of about 2 degrees.

From the perspective of an Earthling, every day on Mars mayfeel like an ice age. According to NASA, temperatures on Marsmay hit a high at noon at the equator in the summer of roughly20 degrees Celsius (70 degrees Fahrenheit), or a low of aboutminus-153 degrees Celsius (minus-225 degrees Fahrenheit) at thepoles.