"Fossils are rare in rocks from the era before multicellular life," a NASA scientist explained to me privately, agreeing that microorganisms would be very difficult to ever find. "But larger fossils are fairly common in more recent strata. If Mars ever had macroscopic life, whether truly multicellular or in the form of large colonies like stromatolytes, fossils would be discoverable with a reasonable search."

Another NASA geologist, and an old friend, chortled as he recounted the official reaction to questions the week before about the millimeter-long "curly macaroni", which was seen in a cross section after Opportunity dug a hole into the rock. It not only had a spiral shape but appeared to be at the head of a burrow.

"This feature has the team in Pasadena squirming," my old friend told me. "They want it to be an artifact [that is, not "real"]."

More recent suggestions are that the curlicue wasn?t rock at all, but something created by the abrasion of the drill.