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Space researchers have been virtually in orbit since mid-August, when possible evidence of primitive life on ancient Mars was published in Science. Almost everyone, including the US president, was caught up in the excitement over whether our long-held imaginings about life on Mars might be true.
But Professor of Chemistry Emeritus Klaus Biemann doesn't recommend booking a ticket for Mars in our lifetime. And Richard Binzel, associate professor of planetary sciences, says that the cited evidence for ancient microscopic life, while fascinating, is by no means conclusive.
"It's one of the more astonishing results in plantary science in the past 19 years," Professor Binzel said at a Family Weekend open house on October 4.
"This paper has had an enormous impact on the space program," Professor Biemann, former team leader of NASA's 1976 Viking search for organic compounds experiments, said at a seminar entitled "Past Life on Mars? Fact vs. Hype" on September 25. "But should we send people to Mars? My personal feeling is it's ridiculous in the next 100 years."
Professor Biemann cautioned against being overly optimistic about life on Mars, because the conclusion reached in the Science paper can't be proven or disproven any time soon. The 1976 Viking mission, which sent landers to the surface of Mars for three Martian years, did not find any trace of organic materials, he noted. A US mission may bring back the first sample of Martian soil in the year 2005.
Though the ALH84001 meteorite was discovered in 1984, it was not considered Martian until 1993 because it is much older than Mars meteorites discovered earlier. The previous 11 meteorites that scientists believe to be from Mars were crystallized about 1.5 billion years ago, but ALH84001 was crystallized 4.5 billion years ago. It fell into the Antarctic about 13,000 years ago and was discovered after it was exposed by the movement of ice.
The meteorite almost certainly was blasted from a Martian surface impact some 16 million years ago into an orbit that eventually intersected with Earth's. It has a similar composition to 11 other SNC meteorites that have been found on Earth, which are igneous rocks made of shergottite, nakhlite and chassignite, Professors Biemann and Binzel explained. The ALH84001 meteorite was also found to have the same oxygen isotope ratio as the other SNC meteorites.
Upon further study, scientists discovered that the meteorite contained carbonate globules younger than the rock itself that formed along fractures where water once penetrated. On the surfaces of the globules are "microfossils" shaped like "little tiny Cheetos" that resemble the remains of terrestrial microorganisms although they are 100 times smaller, Professor Binzel said. The presence of polycyclic aromatic hydrocarbons associated with biological decay (substances that are ubiquitous on Earth but not found on other Mars meteorites), as well as magnetite and iron sulfate precipitates, are further indications of one-time primitive life.
The paper's authors wrote that while none of the pieces of evidence is conclusive by itself, that collectively they demonstrate the past existence of a microorganism, Professor Binzel said. The scientific community as a whole believes that the study was carefully done, but that it does not in fact offer definitive evidence, he added.
SCIENCE IS THE WINNER
"We're at a bit of a stalemate," he said. "What we're going to see over time is a bit of scientific debate as more and more researchers get hold of samples" of ALH84001. "As different groups come up with evidence one way or the other, it's not whether one side `wins.' The clear winner is the scientific process. This is a great case of science at work." Future work will include a search for the presence of amino acids as tracers for life, examination of the microfossils' wall structure, and an attempt to find microfossils "caught in the act" of reproducing, he said.
Professor Biemann said it will be nearly impossible to prove or disprove the claims by visiting Mars itself anytime soon. Even when a mission is sent to collect samples, it will be difficult to position the land rover in a spot where there may be organic compounds. Also, the surface of Mars is made of dust and is highly irradiated, so scientists will have to drill down at least one meter to get a sample.
A version of this article appeared in MIT Tech Talk on October 9, 1996.