New evidence to rewrite Martian climate history

Geologists from Brown University have found new evidence that glacier-like ice deposits advanced and retreated multiple times in some regions of Mars in the recent past.

For the study, the researchers looked at hundreds of gully-like features found on the walls of impact craters throughout the Martian mid-latitudes.

They concluded that many of those gullies were formed by meltwater from icy deposits, which are known to have covered the Martian mid-latitudes within the last two million years.

The study also turned up evidence of multiple gully-forming events, suggesting that these ice deposits waxed and waned several times over the last several million years - relatively recently in Mars' 4.5-billion year history.

"These recent climate cycles have been predicted by computer models, but have not been documented with widespread geological evidence until now," said Jay Dickson, researcher at Brown university.

New research shows that gullies have been episodic across the entire southern hemisphere, a distribution that is required for this to be a signal of global climate change.

The researchers found that this recent Martian ice age was likely linked to the planet's wobbly rotation around its axis.

Currently, the angle of Mars' axis -- its obliquity -- is about 25 degrees, fairly close to that of Earth.

But because Mars lacks a large moon to stabilise its rotation, its recent obliquity oscillates between around 15 degrees and as much as 35 degrees.

Earth's obliquity, in contrast, varies only 2.4 degrees.

Computer models predict that when the obliquity of Mars exceeds 30 degrees, increased sunlight at the poles causes water in the ice caps to be freed into the atmosphere.

That water is transported and deposited closer to the equator in the form of glacial snow and ice.

Mars is known to have crossed the 30-degree threshold in obliquity several times during the last 20 million years.

"So if obliquity drives ice ages, there should be evidence for multiple glacial periods in the Martian midlatitudes," the team noted.

The work also bolsters the idea the many of gullies were carved by flows of liquid water, suggesting the mid-latitudes of Mars could be a place to look for signs of past life, they concluded.

The study appeared in the journal Icarus.