Have trace fossils been found on Mars? In browsing the first new batch of 2018 Curiosity Mars Hand Lens Imager (MAHLI) photos snagged from Sols 1922 and 1923, researcher Barry DiGregorio speculates whether or not the Red Planet prowler has found trace fossils on Mars. DiGregorio is a research fellow for the Buckingham Centre for Astrobiology in the United Kingdom and author of the nonfiction books “Mars: The Living Planet” and “The Microbes of Mars.”
“They look remarkably similar to Ordovician trace fossils I have studied and photographed here on Earth,” DiGregorio told Inside Outer Space. “If not trace fossils, what other geological explanations will NASA come up with?”
So I posed that question to Ashwin Vasavada of NASA’s Jet Propulsion Laboratory in Pasadena, California. He’s project scientist for the Curiosity Mars rover.
Vasavada reports that the eye-catching features are very small, probably on the order of a millimeter or two in width, with the longest of the features stretching to roughly 5 millimeters. “So they are tiny,” he advised Inside Outer Space.
Serendipitously, they were first spotted in black and white imagery. The features were compelling enough for the science team to roll back Curiosity to further examine them, Vasavada says, making use of the robot’s MAHLI – a focusable color camera mounted on the rover’s arm.
“These were unique enough, given the fact that we didn’t know they were there…we thought we should go back,” Vasavada explains.
Christopher Edwards, a planetary geologist at Northern Arizona University in Flagstaff, Arizona, and Curiosity mission team member also made note of the plan to wheel Curiosity back to study the dark toned “stick-like” features.
“This site was so interesting that we backtracked to get to where the rover was parked for this plan,” Edwards explains in a January 3 mission update. “In the workspace in front of the rover, we have some very peculiar targets that warranted some additional interrogation.”
Geological or biological processes?
As to the origin of these odd features – geological or biological processes – it’s in TBD limbo.
Regarding trace fossils on Mars, “we don’t rule it out,” Vasavada responds, “but we certainly won’t jump to that as our first interpretation.”
Rather, close-up looks at these features show them to be angular in multiple dimensions. That could mean that they are related to crystals in the rock, perhaps “crystal molds” that are also found here on Earth, Vasavada adds. Crystals in rock that are dissolved away leave crystal molds, he said.
Still, that’s just one of a few possibilities, Vasavada explains. “If we see more of them…then we begin to say that this is an important process that’s going on at Vera Rubin Ridge.”
Curiosity scientists have been discussing the newly found and novel features, Vasavada says, attempting to discern just what they signify.
In the end, however, can the Mars robot discern a crystallization process versus a biological process?
“That’s pretty challenging on Earth to distinguish those two things without being able to put these things into a lab to look for the presence of organics,” Vasavada points out. “We have a very limited capability overall to understand whether something is biological or not.”
Meanwhile, along with new MAHLI imagery, Curiosity’s Chemistry and Camera (ChemCam) and its Alpha Particle X-Ray Spectrometer (APXS) are also inspecting the features for clues as to their nature.
“The Curiosity images really pique our curiosity,” explains Pascal Lee, a planetary scientist at the Mars Institute and SETI Institute in Mountain View, California. Still, given the imagery, “it’s hard to tell what the wiggly sticks are,” he said, “and a strictly mineral origin is, of course, the most plausible.”
But as a field geologist, Lee said that on first view of the feature “the immediate thought that came to my mind is bioturbation.”
Bioturbation is the process through which organisms living in sediments can disturb the very structure of these sediments.
“A common example of bioturbation is the formation of worm burrows. The burrows, once refilled with sediments, fossilized, and then exposed by erosion, can end up looking like wiggly sticks,” Lee tells Inside Outer Space.
Is any of this relevant to Mars?
“Well, bioturbation at the scale of the features seen in the Curiosity imagery would imply macroscopic multicellular organisms at work, so something that would have evolved far beyond unicellular life,” Lee responds. “To claim that we’re seeing bioturbation on Mars – which I did not say – would be an extraordinary claim.”
Lee adds that he’s reminded of what noted astronomer, Carl Sagan, would say: “Extraordinary claims require extraordinary evidence.”
The upshot of the Curiosity observations is need for a lot more evidence to make any such claim, Lee said, including evidence that allows ruling out less extraordinary claims.
“But I have to say, the imagery is really intriguing, and I hope Curiosity spends more time in the area to get to the bottom of this,” Lee concludes. “This is exciting!”
Also finding the Mars rover images interesting is astrobiologist, Dirk Schulze-Makuch, a professor at the Technical University Berlin, Germany, and an adjunct professor at Arizona State University and Washington State University. His latest book, co-authored with MIT researcher, William Bains, is The Cosmic Zoo: Complex Life on Many Worlds.
“Cool, looks like bioturbation and would likely be as such identified if the image would be from Earth,” Schulze-Makuch says. “But concretions can look quite similar and in case of Mars, it´s being more likely concretions.”
via Leonard David