Water has flowed on the surface of Mars within the past five years, according to evidence that suggests the Red Planet could be capable of harbouring life.

Images taken from an orbiting spacecraft have found two fresh features in the Martian landscape scientists think were formed by torrents of water flowing as recently as 2001.

The remarkable observations demonstrate for the first time that modern Mars may not be as dry and barren as is usually assumed. Wherever liquid water is found on Earth there is also life, and most scientists consider its presence a prerequisite for the existence of primitive extraterrestrial organisms. If it exists on Mars, it raises the very real prospect that life may not only have evolved there in the past, but could survive there today.

Ice has been detected at the Martian poles, and many of the planet’s features are known to have been formed by water in the distant past. But there have been few firm indications that it is present today, in liquid form. That has changed with the latest images from Nasa’s Mars Global Surveyor spacecraft. Between 1999 and last year, it took pictures of thousands of gullies, which have since been examined for significant change.

At two sites, the Terra Sirenum crater and an unnamed second crater in the Centauri Montes region, channels were seen in later images containing fresh, pale-coloured deposits that appear to have been left by flowing water.

At Terra Sirenum, the image changed dramatically between December 2001 and April 2005, and at Centauri Montes the changes happened between August 1999 and February 2004. The character of the deposits left by whatever cascaded briefly down these slopes, particularly the way it has flowed around solid obstacles, points firmly towards water rather than dust as the cause of the new features.

“The observations suggest that liquid water flowed on Mars during the past decade,” Mike Malin, chief scientist for the camera that took the pictures, said. In each case, the amount of water that formed the features would have been approximately equivalent to five to ten swimming pools full, Michael Meyer, Nasa’s lead scientist for Mars exploration, said. “On Mars, the atmospheric pressure is so low that it’s going to be boiling as it comes off. You’ve heard of a smoking gun. This is a squirting gun.” John Murray, of the Open University, one of the lead scientists on the European Mars Express spacecraft, agreed that the new channels appear to have been formed by water. He said: “It is a really interesting and tantalising find. There is so much evidence of past water flow, but if this is right then the same is happening at the present time.

“This is one more place in which we might possibly find life. If you have microorganisms frozen in water deposits just below the surface of Mars, then yes, these could be revived.

“It’s a small possibility but it is a possibility: on Earth, microbes can exist for tens of thousands of years like that and still be revived.”

The images represent a fitting swansong for the Mars Global Surveyor, which fell out of contact with mission control last month after ten years in orbit around the planet.

Philip Christensen, of Arizona State University, said: “Five years ago, we were talking about water on Mars five million years ago. Today we can honestly talk about water on Mars today. That . . . has really changed how we think about Mars and how we should think about exploring Mars.”

Details of the new discovery are published in the journal Science.

Liquid history

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