Martian clues to life from space

Martian meteorite ALH84001 fell into Antarctic ice

Scientists have found evidence that a well-known meteorite would have stayed cool enough to allow lifeforms, if present, to survive the journey from Mars to Earth.

The Martian meteorite caused a sensation in 1996 when the American space agency Nasa said it appeared to contain signs of life.

But other scientists later disputed the claim, presenting evidence that the meteorite was contaminated by the ice into which it fell.

The new finding is likely to fuel debate over whether the first simple forms of life on Earth could have originated in space.

Low temperature

A team of scientists in the United States and Canada studied have been studying the meteorite known as ALH84001.

The rock was originally blasted off the face of Mars in a huge impact. After millions of years drifting in space, it finally fell to Earth in Antarctica.

An analysis carried out by the researchers suggests that the interior of the meteorite would never have reached a temperature of more than 40C (104F) during its turbulent journey from the Red Planet.

In theory, this temperature is cool enough to allow any microorganisms within the meteorite to survive.

'Seeds' of life

The study does not present any new evidence about whether lifeforms could have been present.

But it will add to the debate about whether life on Earth could have been "seeded" by organisms from space, as some researchers have proposed.

Scientists have speculated that meteorites could be a way of passing lifeforms from one planet to another, including Earth.

But critics of the theory argue that any meteorite would reach such a high temperature either before or during its entry into our planet's atmosphere that any microscopic life would be killed off.

Writing in the journal Science, Benjamin Weiss, who led the research, said: "These data support the hypothesis that meteorites could transfer life between planets in the Solar System."