Washington, Dec 5 : Researchers at the California Institute of Technology (Caltech) and their colleagues have found evidence of ancient climate change on Mars in rocks on the planet.

Using stereo topographic maps obtained by processing data from the high-resolution camera onboard NASA's Mars Reconnaissance Orbiter, the Caltech scientists, led by Kevin Lewis and Oded Aharonson, along with John Grotzinger, identified and measured layered rock outcrops within four craters in the Red Planet's Arabia Terra region.

The layering in different outcrops occurs at scales ranging from a few meters to tens of meters, but at each location the layers all have similar thicknesses and exhibit similar features.

Based on a pattern of layers within layers measured at one location, known as Becquerel crater, the scientists propose that each layer was formed over a period of about 100,000 years and that these layers were produced by the same cyclical climate changes.

In addition, every 10 layers were bundled together into larger units, which were laid down over an approximately one-million-year period.

In the Becquerel crater, the 10-layer pattern is repeated at least 10 times.

This one-million-year cycle corresponds to a known pattern of change in the obliquity of Mars caused by the dynamics of the solar system.

"Due to the scale of the layers, small variations in Mars's orbit are the best candidate for the implied climate changes. These are the very same changes that have been shown to set the pacing of ice ages on the Earth and can also lead to cyclic layering of sediments," said Lewis.

During phases of lower obliquity on Earth, polar regions are less subject to seasonal variations, leading to periods of glaciation.

The Martian tilt varies by tens of degrees over a 100,000-year cycle, producing even more dramatic variation.

When the obliquity is low, the poles are the coldest places on the planet, while the sun is located near the equator all the time.

This could cause volatiles in the atmosphere, like water and carbon dioxide, to migrate poleward, where they'd be locked up as ice.

When the obliquity is higher, the poles get relatively more sunlight, and those materials would migrate away.

Another effect of the changing tilt would be a change in the stability of surface water, which alters the ability of sand grains to stick together and cement in order to form the rock layers.

"This study gives us a hint of how the ancient climate of Mars operated, and shows a much more predictable and regular environment than you would guess from other geologic features that indicate catastrophic floods, volcanic eruptions, and impact events," said Lewis.

ANI