Martian feature only a pit, not a bottomless cavern, reveals HiRISE image

An extremely dark feature on Mars is probably just a pit - not the entrance to a deep cavern that future astronauts could call home, a new image by NASAs Mars Reconnaissance Orbiter has revealed.

London, Aug 31 : An extremely dark feature on Mars is probably just a pit - not the entrance to a deep cavern that future astronauts could call home, a new image by NASA's Mars Reconnaissance Orbiter has revealed.

Viewed from directly overhead, the dark spot showed no evidence of walls or a floor, leading astronomers operating the High Resolution Imaging Science Experiment (HiRISE) camera to suspect that the pit was the opening to a cavern.

The 150 - by 157-metre feature had astronomers excited since it was first noticed in an image taken by the HiRISE camera on May 5, 2007.

Caves are a good place to search for life as they offer protection from intense ultraviolet radiation from the Sun. They could also provide shelter for any future human visitors to Mars.

The new image, taken on August 8, from a different angle, however suggests that the feature is just a vertical shaft cutting into the surface.

The image reveals a wall on the feature's eastern side.

Although it is not clear how deep the pit is, because its floor has still not been seen, but the HiRISE team says it must be at least 78 metres deep.

They say similar "pit craters" form on the flanks of volcanoes in Hawaii when lava deep underground drains away, causing the overlying rock to collapse downward, forming a well.

They said although this particular feature did not turn out to be a cave entrance, Mars may have caves in the form of intact "lava tubes"- long tube-shaped cavities sometimes left behind when underground lava drains away.

According to New Scientist, some collapsed lava tubes are known on Mars and intact ones may well be present too.

ANI