Life on Mars hopes raised

Pathfinder's view of Mars: A lot more work needs to be done

By Dr David Whitehouse BBC News Online science editor

Scientists have found "intriguing" new evidence that may indicate there is life on Mars.

An analysis of data obtained by the Pathfinder mission to the Red Planet in 1997 suggests there could be chlorophyll - the molecule used by plants and other organisms on Earth to extract energy from sunlight - in the soil close to the landing site.

Researchers stress their work is in a very preliminary state and they are far from making definite claims.

Even so, the work is attracting much attention in the scientific community and will come under intense scrutiny when it is presented to an astrobiology conference in the US next week.

Chlorophyll on Earth

A pigment found in plants, some algae, and bacteria that allows these organisms to catch sunlight

This energy is used to drive photosynthesis, a process that converts carbon dioxide and water into the simple sugar glucose

Photosynthesis is the starting point for nearly all life on Earth

It is the great abundance of chlorophyll in leaves and other tissues that makes plants appear green

Dr Carol Stoker, from the American space agency's (Nasa) Ames Research Center, confirmed the findings to BBC News Online but cautioned that they were "not ready for the big time".

Early data

Mars Pathfinder mission touched down in the Ares Vallis region of Mars in July 1997. It took many images of the surrounding area and released a small rover to sample rocks.

A detailed analysis of the images of the landing site now reveals two areas close to Pathfinder that have the spectral signature of chlorophyll.

According to experts it might be highly significant - or could be just a patch of coloured soil.

Dr Stoker's team scrutinised the so-called Superpan, which is a high-resolution, highly processed series of superimposed images produced by Pathfinder's camera.

It is a multispectral panorama of the landing site recorded in 15 regions of the spectrum, and contains a wealth of information about rock types, colours and textures.

Sojourner: A rover was used on the mission to take a closer look at the surroundings

Knowing the spectral signature of chlorophyll, the researchers wrote a computer program that systematically scanned the Superpan for any pixels of interest.

Specifically, the program looked for the spectral signature associated with red light absorption by chlorophyll.

Previous searches for evidence of chlorophyll in Pathfinder's pictures were carried out shortly after it landed.

Some tentative indications were seen but they were later dismissed as "possible image misregistration".

Two patches

In Dr Stoker's study six regions of the Superpan matched positive for the chlorophyll signature.

For each of the regions, a full spectrum was plotted out and their exact position in the Superpan was then carefully examined.

All of the detections occurred close to the camera. This is to be expected say the researchers, as these are the areas where the camera has the highest sensitivity and resolution.

Close examination revealed that four of the cases occurred on the Pathfinder spacecraft itself. But two regions showed a chlorophyll signature in the soil around Pathfinder.

Given the controversial nature of their findings and the early stage of the research, the scientists want to hold back any claims about what they may have found until they have done more work and prepared a detailed paper for submission in a scientific journal.