Washington, Dec 17 : A new study has suggested that rock varnish could provide a niche habitat for microbial life on Mars and in other extraterrestrial environments devoid of liquid water.

The study was undertaken by a research team led by Kimberly R. Kuhlman, of the Tucson-based Planetary Science Institute.

The team found bacteria associated with rock varnish in an area where the surrounding soils were essentially devoid of life.

Rock varnish is an extremely slow-growing coating that forms on the surfaces of rocks in arid and semiarid climates.

In Southwestern deserts, it often appears as a tough, dark stain on light-colored canyon walls. Ancient petroglyphs are often found etched into rock varnishes.

Kuhlman's team analyzed samples of rock varnish collected from the Yungay region of Chile's Atacama Desert, which is the closest analog to Martian environments found on Earth.

The bacteria apparently get most, if not all of their moisture from fog, according to Kuhlman.

The bacteria also are aerobic. So if Martian forms exist, they would have adapted to survive their planet's low-oxygen atmosphere, she added.

Rock varnish, which consists of clay glued together with iron and manganese oxides, forms very slowly and is very thin.

It adds only 1 to 40 nanometers in thickness per year, and tends to be no more than 500 millimeters thick, regardless of age.

Similar rock coatings may exist on Mars because photos returned by every Martian lander show what looks like rock varnish coating the rocky surfaces.

If it is rock varnish, it could provide bacteria with the same benefit it does on Earth - protection form ultraviolet radiation.

Since many bacteria cannot be cultivated in the lab, Kuhlman's team used culture-independent methods to identify many of the species found in the Atacama varnish.

They looked for adenosine triphosphate, a molecule that provides energy for cells that is found in all living things on Earth, and they also identified DNA from 32 species.

In addition, they were able to produce live cultures of other bacteria.

Many species were related to bacteria found in the air or water, suggesting that their ancestors may have been carried into the area during wetter periods and then evolved in the varnish niche as conditions changed.

A similar scenario might have played out on Mars, with varnish bacteria surviving from the planet's wetter eras. (ANI)