Is there life on Mars?: Study of decades-old meteorite casts doubt on presence of life on the planet

A meteorite from Mars that caused a splash here on Earth decades ago contains no sign of ancient, primitive life on Mars, after all, say scientists.

NASA announced in 1996 that organic compounds in rocks may have been deposited by living organisms. Many scientists were sceptical, and researchers have been chipping away at it over the past few decades, most recently by a team led by Andrew Steele of the Carnegie Institution for Science.

According to Steele, tiny samples from the meteorite show the carbon-rich compounds were actually produced by water flowing over the rock for a prolonged period. The research was published in Science.

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In 1984, a 4lb (2kg) rock was discovered in Antarctica. During Mars' early, wet past, at least two impacts near the rock heated the surrounding surface, before a third impact bounced the rock away from the planet millions of years ago. 

The meteorite drifted through space for millions of years before landing on an ice field in Antarctica thousands of years ago. This small grey-green fragment was named Allan Hills 84001 after the hill where it was found.

^{This high-resolution scanning electron microscope image released by NASA 19 March 1999, shows an unusual tube-like structural form that is less than 1/100th the width of a human hair in size found in meteorite ALH84001.}

Researchers believe tiny globs of carbon are the result of groundwater moving through cracks in the rock, while it was still on Mars. They said that the same thing can happen on Earth and could explain the presence of methane on Mars.

However, two scientists who were involved in the original study disagree with the current findings, calling them "disappointing". According to an email exchange, they are sticking with their 1996 findings.

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In spite of the fact that the data presented incrementally add to our knowledge about (the meteorite), the interpretation presented is neither new nor supported by the research, wrote astromaterial researchers at Nasa's Johnson Space Center in Houston, Kathie Thomas-Keprta and Simon Clemett.

They said unsupported speculation does little to clarify the origin of organic matter in the meteorite.

Steele says his team's research findings are possible as a result of advances in technology. In his view, the measurements by the original researchers were commendable and their life-claiming hypothesis was a reasonable interpretation at the time. 

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The team, which includes NASA, German, and British scientists, took care to present the findings as an exciting discovery about Mars rather than a study to disprove the original premise, he added.

Bringing samples back to Earth for analysis is the only way to prove if Mars had microbial life in the past or if it does now, according to Steele. 

(With inputs from agencies)