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Scientists Give Even Odds Concerning 'Life on Mars'


University of Arizona News Services

From: Kevin Guerrero, Arizona Space Grant Intern for News Services

Contact(s): Timothy D. Swindle, 520-621-4128,

October 29, 1997
Scientists give about even odds concerning 'life on Mars' question; Less sure of Allan Hills meteorite evidence, preliminary survey says

EDITORS: Swindle leaves Tucson for India, then Antarctica, on Nov. 3.

Did life exist on Mars or not? According to Timothy D. Swindle, it's not an either/or question.

Swindle, an associate professor in the Lunar and Planetary Laboratory at The University of Arizona in Tucson, conducted a survey of his colleagues at the 28th annual Lunar and Planetary Science Conference in Houston in March. He asked respondents to assess two things: the possibility that life existed on Mars and the likelihood that Mars meteorite ALH84001 contains evidential features of martian life.

A group of NASA scientists announced on Aug. 7, 1996, that the meteorite ALH84001 contains what might be evidence for past life on Mars. Found in the Allan Hills ice fields of Antarctica in 1984, this meteorite has stirred up a lot of controversy.

As part of a neutral team, Swindle took part in the initial presentation of ALH84001 at the Division of Planetary Science Meeting last year in Tucson.

It was at this meeting that Swindle first started thinking about the question of life on Mars in the context of the controversy. He realized that the answer, for the present anyway, would not be so neatly black-and-white. The controversy over the meteorite and the lack of conclusive evidence for life on Mars made the question difficult to answer.

"I conducted the survey because the yes or no question was too restrictive," Swindle said.

Of all the 125 respondents to the survey, the median response was a 56 percent chance that life has existed at some point on Mars. In response to the second question, of whether the features of ALH84001 provide evidence of martian life, the likelihood was much lower: the median response was a mere 20 percent chance.

Swindle is quick to point out, however, that the survey has a few limitations. Only one-tenth of the scientists at the Houston Conference responded, which is not a scientific majority. And of the 125 respondents, only 19 had published something regarding the origin or early evolution of life.

According to Swindle, it is also important to realize that science is not a democracy.

"The process of acceptance or rejection of an idea is driven by experiments, models, and theories, and is seldom instantaneous," Swindle said.

Despite these limitations, the survey reveals that the current scientific attitude toward life on Mars is more complicated than most people believe. The issue has not been conclusively settled: it may take ten to twenty years to know conclusively whether life existed on Mars. While those surveyed may believe there is more than a 50 percent chance that life existed at some point on Mars, they don't believe that ALH84001 provides convincing evidence for that claim. The survey also reveals that, in general, those who studied Mars gave higher estimates than those who studied meteorites.

Swindle hopes to conduct the survey again in a few years because he wants to know how scientific attitudes change. The big change in attitude, he predicts, will come when we actually bring rocks back from Mars.

Until a space expedition actually returns with this evidence, Swindle will examine meteorites on Earth. On November 3, he leaves for a six week expedition among the mountains of Antarctica to search for meteorites -- some of which may from Mars and be more decisive evidence than ALH84001.

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