PARIS -- Three-quarters of the 250 Mars science experts meeting to analyze the results from U.S. and European Mars probes believe life could have existed on Mars in the past, and 25 percent think life could be there even now, according to a poll released Feb. 25.

The poll was announced during a press briefing following the First Mars Express Conference, held Feb. 21-25 at the European Space Agency's Estec technology center in Noordwijk, Netherlands.

The results perhaps reflect the sober caution of scientists who refuse to jump to conclusions before conclusive evidence is in about the No. 1 issue on the minds of everyone attending the conference, held to review a year's operations of Europe's Mars Express orbiter.

Everett K. Gibson of NASA's Johnson Space Center in Houston, who attended the meeting as a Mars interdisciplinary scientist reviewing the results of all the Mars experiments, said the available data lends credence -- but as yet offers no proof -- to the idea that the methane and formaldehyde present in Mars' atmosphere is evidence of underground life.

Gibson said definitive proof likely will require a future Mars mission carrying sophisticated drills to penetrate beneath the Mars surface to take samples directly or -- a preferred option -- to return them to Earth for laboratory evaluation. "Mars is revealing her secrets, but slowly," Gibson said. "We need those samples or in-situ measurements."

In a series of presentations on each of Mars Express' seven experiments, several scientists stopped just short of saying that the evidence so far points to life buried under the surface of Mars away from the ravages of the solar wind.

One possible explanation for the absence of liquid water on the surface of the planet is that Mars, which unlike Earth does not have a protective magnetic field, is being shorn of its surface by the solar wind. An estimated 100,000 kilograms per day of Mars surface material is blown off the planet, according to Stas Barabash, lead scientists for the Mars Express ASPERA-3 experiment, which measures the phenomenon.

Vittorio Formisano, lead scientist for the Mars Express Planetary Fourier Spectrometer, which is investigating Mars' atmosphere, said the differing levels of concentration of methane and formaldehyde are cause for optimism that life exists under the surface.

"We need more work for a final conclusion," Formisano said, adding: "Life is probably the only source that could produce so much methane. The question is not any more, Was there life on Mars? The question is: Is there life on Mars today?"