Findings hint at life on Mars

A "worm" structure was found on ALH84001 in 1996

By BBC News Online science editor Dr David Whitehouse

Tiny magnetic grains found in a meteorite from Mars are identical to grains produced by some strains of bacteria on Earth, claim researchers.

If you did not know that this rock was from Mars, and if you studied it, you would conclude that it contains evidence for past life

Dr Kathie Thomas-Keprta, Lockheed Martin Corporation

The new findings will reopen the debate about whether the rock contains fossil evidence of ancient life on the Red Planet.

The study, published in the journal Geochimica Cosmochimica Acta, took four years to complete. Those behind it include some of the original scientists that first put forward the controversial idea that odd structures on the meteorite called ALH84001 represented the remains of Martian microbes.

Lead author Dr Kathie Thomas-Keprta, of the Lockheed Martin Corporation, told BBC News Online that the new analysis should be looked at objectively by critics of their 1996 announcement.

Careful study

The original claims about ALH84001 rested on four lines of evidence.

These were the life-like shapes of some features found in the rock, two aspects of its chemical composition and the existence of tiny magnetic crystals similar to crystals produced by some bacteria found on Earth.

An electron microscope picks out magnetite crystals from the Mars rock

In a watershed paper, the first detailed analysis to emerge after the original announcement, Dr Kathie Thomas-Keprta and colleagues extracted nearly 600 crystals of magnetite from ALH84001 by dissolving tiny sections of the rock in acetic acid.

The tiny crystals were then examined with an electron microscope. "They are so small you could fit a billion of them on the head of a pin," Dr Thomas-Keprta said.

The objective was to analyse in detail the shapes of the crystals. Of 594 crystals studied, 164 shaped like elongated prisms were chosen for further investigation.

'Indistinguishable' crystals

For a year, Dr Thomas-Keprta looked at them and categorised their structure. The result was a statistical analysis of the grains based on six measured parameters.

She then looked at grains of magnetite produced naturally by a strain of terrestrial bacteria called MV-1.

Magnetite crystals produced by terrestrial bacteria look very similar

By all available criteria, the magnetite grains from the Mars rock and MV-1 bacteria were identical.

"If you take an individual magnetite crystal from the Mars rock and one produced by terrestrial bacteria you would see that they are indistinguishable," Dr Thomas-Keprta said.

She added that she had to take great care in the laboratory because if the two sets of grains were mixed up it would be impossible to separate them again.

Sample return

Although the research team say they would never claim to have absolute proof that there was life in the Mars rock, they are stating that this evidence is strong.

Dr Thomas-Keprta summarises the groups findings in a way that some of the critics of the original 1996 claims will find challenging.

Just over a dozen Martian meteorites like ALH84001 have been found on Earth

"If you did not know that this rock was from Mars, and if you studied it, you would conclude that it contains evidence for past life. But some people just cannot make the leap to believe that it may contain evidence of past life on Mars."

On Earth, bacteria that produce tiny grains of magnetite are commonplace. Some scientists are excited at the prospect of looking for them on Mars, especially in those newly identified regions of sedimentary rocks that caused a sensation when details of their existence were revealed last week.

Unfortunately, looking for them would not be possible on the Red Planet given today's technology. The rocks would have to be returned to the Earth for analysis.

Dr Thomas-Keprta said: "I think our critics should look at this paper very seriously. I think that when people study it, support could be gathered from other scientists."

Dissenting voices

But the first signs are that critics will be hard to impress. Professor John Bradley, of Georgia Technical School of Materials and Technology, said the latest paper would be viewed by some as "Custer's last stand" in the great ALH84001 Martian meteorite debate.

The paper falls far short of definitively ruling out a non-biogenic origin for the elongated prismatic magnetite crystals in ALH84001

Prof John Bradley, Georgia Technical School of Materials and Technology

He told BBC News Online: "This latest paper presents a very impressive comparative study of the properties of terrestrial biogenic magnetites and a selected subset of the magnetite crystals in ALH84001.

"However, the conclusion remains essentially the same as that of the 1996 paper, i.e. some of the magnetite nanocrystals in ALH84001 are consistent with biogenic magnetites. To my knowledge there has never been any disagreement on this issue.

"But what the new paper fails to establish is that the properties of the magnetite nanocrystals are unique to biogenic magnetites. The paper falls far short of definitively ruling out a non-biogenic origin for the elongated prismatic magnetite crystals in ALH84001."

Dr Kathie Thomas-Keprta and colleagues do not feel threatened by such comments. They believe that future lab experiments will support them and have promised new results in the near future.