At a Washington, D.C., news conference, scientists showed magnified pictures of a four-pound Martian meteorite riddled with wormy blobs that looked like bacterial colonies. The researchers explained how they had pried numerous clues from the rock, all strongly supporting their contention that microscopic creatures once occupied its nooks and crannies.
It was arguably the space agency's most imagination-gripping moment since Apollo. Space buffs and NASA officials said that it just might be the scientific discovery of the century.
"If the results are verified," the late Carl Sagan pronounced, "it is a turning point in human history."
Ten years later, the results have not been verified. Skeptics have found non-biological explanations for every piece of evidence that was presented on Aug. 6, 1996. And though they still vigorously defend their claim, the NASA scientists who advanced it now stand alone in their belief.
"We certainly have not convinced the community, and that's been a little bit disappointing," said David McKay, a NASA biochemist and leader of the team that started the scientific episode.
But even though the majority of his colleagues don't buy his "life on Mars" theory — McKay's own brother, also a NASA scientist, is one of his most prominent critics — many say they respect him and greatly appreciate his efforts.
The announcement and the technical paper that followed it practically created exobiology, the scientific field that investigates the potential for life on other planets.
"Without that paper I wouldn't be working in this field," said Martin Fisk, a marine geologist who studies how bacteria survive under the sea floor, partly because their harsh environment may resemble that of extraterrestrial life.
Debating the claim has helped researchers develop standards that will eventually prove useful for evaluating the presence of life in other Martian meteorites or a sample from the red planet. It has given the scientific community ideas about exactly where on the planet they would most like to scoop up a sample, should they ever get to retrieve one.
And it is undeniable that McKay and his colleagues have drawn attention to what is, whether it contains evidence of life or not, a very interesting rock.
The rock in question was discovered in Antarctica, where rocks that fall from the heavens are easy to spot on the icy glacial plains. Its name, ALH84001, indicates that it was the first meteorite found during the 1984 research season in the Allan Hills, an especially meteorite-rich area in the Trans-Antarctic Mountains.
At first ALH84001 was misclassified, so it wasn't until 1993 that researchers even realized the rock came from Mars. That was interesting enough, because at the time fewer than a dozen Martian meteorites were known to science.
But ALH84001 also turned out to be much more ancient than the other known Martian meteorites. At 4.5 billion years old, it dates from a period of Martian history when liquid water, a requirement for the presence of life, probably existed at the now barren planet's surface.