EMBARGOED Mars has a long history of being misinterpreted, from conjurings of apparent
canals that signaled an alien civilization to the infamous NASA photo of a supposed giant face. Now a close-up picture of tiny spheres embedded in a Martian rock has some people seeing fossilized life. This alternate, perhaps hopeful view of a picture taken by NASA's Opportunity Rover and released Monday has been expressed in e-mail messages to reporters and geologists. Mission scientists anticipated it and were ready yesterday with a response.
While the spherules, as the small structures are called, are incredibly interesting, they are not that incredible, according to Steven Squyres, principal investigator for the Mars Exploration Rover (MER) project from Cornell University.
"There simply is no reason to promote a biological origin for these [spherules] when there are so many other, far more probable ways of making them," Squyres told SPACE.com.
Squyres quoted his former teacher and friend, the late Carl Sagan, who popularized the phrase, "Extraordinary claims require extraordinary evidence."
"To claim a finding of fossils on Mars would certainly be extraordinary," Squyres said, "yet there are many different and very ordinary ways in which Nature makes spherical objects of this size by non-biological processes."
Water, maybe
The rover mission is designed to learn whether Mars was once warmer and wetter --
as most scientists believe -- a place that might have supported some form of very simple, microbial life. The spherules, after further investigation, may point in that direction. But water does not equal life, it only sets the stage. Asked if, prior to getting these first close-up images of a Mars rock, he had harbored any hope of finding fossilized life on Mars, Squyres replied: "Never."
"Even on Earth, which has been a warm and life-friendly planet for nearly all of its history, macroscopic fossils [the sort that would show up in a rover image] don't turn up in any real abundance in the geologic record until about 600 million years ago -- less than 15 percent of the planet's history," Squyres explained. "To expect that life could have evolved to that level of complexity in what might have to be less time, on what has surely been a more hostile planet, would be asking far too much."
The spherules are a few millimeters in diameter -- much bigger than a typical bacterium, which would be the sort of thing scientists would expect to find on the red planet if there is any life there.
The spheres are almost surely of a different composition than the rock in which they are embedded, a preliminary analysis showed. Scientists hope to determine what they are made of in coming days with tests by multiple rover instruments. The tiny beads are thought to have formed in one of three ways:
- Ash from a volcanic eruption was suspended in the air, stuck together, and fell from the sky.
- Molten rock from a volcano or a meteor impact froze in mid-air into glass beads.
- Fluid, possibly water, carried dissolved minerals through a rock and "precipitated" grains that grew into spheres, through a process called "concretion."
The last possibility most excites geologists, but more study is needed to determine which of the hypotheses is correct.
Strange colors
In one
strangely colored image of Stone Mountain, the smallish rock with the outsized name in which the spherules are embedded, other spherules are seen scattered about in the surrounding soil. The radical color enhancement -- done purposely to bring out differences in composition between the rock's primary makeup and that of the spheres -- gives the spheres an eerie, perhaps even lifelike appearance. But the colors are not real. In a
true-color image of the same scene, the spheres are unremarkable.Stone Mountain is part of a modest outcropping roughly the height of a single stair step. There is a depressed region at its base -- a shallow crater -- and a higher plateau above. It is not known where the scattered spherules came from.
"It's impossible to know the pedigree of the ones that we see in the soil," Squyres said. "Some of them certainly must have weathered out of the outcrop, but many of them may be from elsewhere, including materials above the outcrop and outside the crater that we haven't been to yet."
Squyres had expected to be asked about whether the spherules were fossils. So he had asked a colleague, Andrew Knoll of Harvard University, to draft a more lengthy explanation for their non-biological origin.
Not biology
"Some small organisms [on Earth] are spheroidal, but not all small spheroidal structures are organisms," Knoll writes. Extraterrestrial structures or chemical signatures can be accepted as biological "only if we can rule out formation by physical processes -- the idea being that while life might vary from planet to planet, physics and chemistry should not."
Knoll continues: "We know that physical processes make structures like those seen in the images," adding that "we do not know of any cells on Earth" that would form fossils that look, in detail, like the structures seen in the Opportunity photograph.
Spherical fossils this big -- a few millimeters in diameter instead of microscopic -- are relatively rare," Knoll explains. And cells do not fossilize as whole, solid structures.
Responding to a specific suggestion that the rover had found small creatures called diatoms, Knoll said: "This is impossible," citing several observed characteristics of the spherules that don't match up.
The spherules are solid or mostly solid, Knoll writes, with holes interpreted to be small cavities known to geologists as vesicles. "This is not a likely consequence of biology."
The Face on Mars
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