Possible evidence of life on Mars
Do Mars Rover Photos Show Potential Signs of Ancient Life?
Johnny Bontemps, Astrobiology Magazine | January 07, 2015
A careful study of images taken by the NASA rover Curiosity has revealed intriguing similarities between ancient sedimentary rocks on Mars and structures shaped by microbes on Earth. The findings suggest, but do not prove, that life may have existed earlier on the Red Planet.
The photos were taken as the Mars rover Curiosity drove through the Gillespie Lake outcrop in Yellowknife Bay, a dry lakebed that underwent seasonal flooding billions of years ago. Mars and Earth shared a similar early history. The Red Planet was a much warmer and wetter world back then.
On Earth, carpet-like colonies of microbes trap and rearrange sediments in shallow bodies of water such as lakes and coastal areas, forming distinctive features that fossilize over time. These structures, known as microbially-induced sedimentary structures (or MISS), are found in shallow water settings all over the world and in ancient rocks spanning Earth’s history.
Nora Noffke, a geobiologist at Old Dominion University in Virginia, has spent the past 20 years studying these microbial structures. Last year, she reported the discovery of MISS that are 3.48 billion years old in the Western Australia’s Dresser Formation, making them potentially the oldest signs of life on Earth.
In a paper published online last month in the journal Astrobiology (the print version comes out this week), Noffke details the striking morphological similarities between Martian sedimentary structures in the Gillespie Lake outcrop (which is at most 3.7 billion years old) and microbial structures on Earth.
Mistaken discover of water on Marx: Science in action
Part I: NASA satellite shows photographic evidence of what appears to be (very salty) liquid water flowing on the surface of Mars today.
Image from NASA’s Mars Reconnaissance Orbiter (MRO)
However, these RSL (recurring slope lineae) may be the result of granular flows like sand and dust. “The study is based on observations made with the High Resolution Imaging Science Experiment camera on the Mars Reconnaissance Orbiter. The RSL have been perplexing scientists since their discovery. Thousands recur during the warmest season on Mars each year, growing longer and darker until they fade in winter. They’re found on steep, rocky slopes on the darkest areas of Mars: the equator, the northern plains, the southern mid-latitudes. Researchers studied 151 RSL at 10 sites and found all ended at similar points, no matter the length of the slope. If liquid had been involved, there would be longer streaks of liquid on longer slopes. But a closer study of the streaks revealed that they behave just like dry grains of sand on active dunes, all settling at the same “angle of repose.” “We’ve shown that RSL are likely granular flows, which changes our assessment of what they mean for flowing liquid water on Mars and points to formation processes with little or no liquid,”
Flows of ‘water’ on Mars may actually be sand, new study reveals, Ashley Strickland, CNN, 11/21/17
An orbiter glitch may mean some signs of liquid water on Mars aren’t real
A new analysis of images once thought to show hints of saltwater suggests they actually don’t. By Lisa Grossman, Science News, 11/21/2018
… Leask and her colleagues found the problem while searching for hydrated salts called perchlorates in maps of Mars taken by the orbiter’s Compact Reconnaissance Imaging Spectrometer for Mars, or CRISM. Perchlorates can lower the freezing point of water by up to 80 degrees Celsius, which could be enough to melt ice in the frigid Martian climate.
Both the Phoenix Mars lander (SN: 4/11/09, p. 12) and the Curiosity rover have detected tiny amounts of perchlorates in Martian soil (SN Online: 9/26/13). “Finding perchlorate was a big deal, because it’s a way to really make liquid water on Mars,” says planetary scientist Bethany Ehlmann of Caltech.
To see if the salts showed up in other locations on Mars, scientists turned to CRISM’s chemical maps, which show how light reflects off of the Martian surface in hundreds of wavelengths. The resulting spectra allow scientists to identify specific minerals on the surface based on the ways those minerals absorb or alter the light.
In 2015, planetary scientist Lujendra Ojha, now of Johns Hopkins University, and colleagues made headlines when the team reported spotting perchlorates in ephemeral dark streaks on Martian slopes using CRISM data. The results were widely interpreted as a sign that salty liquid water flows on Mars today (SN: 10/31/15, p. 17).
CRISM’s camera doesn’t work perfectly, though. It can be thrown off by boundaries between light and dark, like a shadowed region at the edge of a cliff. Some pixels in the orbiter’s camera take a fraction of a millisecond to realize the surface color changed, so they record an extra spot of light or dark where it shouldn’t be. Planetary scientists have software to correct for these “spikes” in the spectra and make the data more reliable and easier to read.
But the correction sometimes introduces dips in the spectra at the same wavelengths as perchlorates, Leask and Ehlmann and their colleagues found. “We cleverly created a way to get rid of the spiky noise,” Ehlmann says. “But for 0.05 percent of the pixels, it smooths out in a way that looks like perchlorate.”
The researchers found the glitch while looking for small signs of the salts in CRISM images. Assuming that the orbiter would have already spotted large deposits of perchlorates if they existed, the team wrote an algorithm to find smaller traces that covered fewer than 10 pixels in a CRISM image. And the scientists started seeing perchlorates everywhere, including Jezero crater, which NASA announced was selected as the landing site for the Mars 2020 rover on November 19 (SN Online: 11/19/18).
“We were like, oh my gosh!” Ehlmann says. If Mars 2020 lands near a potentially habitable environment, the rover team would have to sterilize the spacecraft more stringently, to avoid accidentally poisoning the water with Earth microbes (SN: 1/20/18, p. 22). “You don’t want to send your dirty spacecraft and kill all the Mars life.”
But on closer inspection, Leask and her colleagues noticed that perchlorates seemed to be showing up in places where it made no geologic sense for the salts to form — and especially along the boundaries between light and dark surfaces. That made the team suspect that the spike-smoothing strategy might be introducing an error.
For months, Leask painstakingly examined every perchlorate pixel in the raw data, before the spike-removing correction had been applied. “We knew instantly that some of [the signs] were not real,” she says. It turned out that none of them were.
“I think [Leask] is definitely onto something here,” says planetary scientist Jennifer Hanley of the Lowell Observatory in Flagstaff, Ariz., who was a coauthor on the 2015 study but was not involved in the new work. Looking at the processed data and the raw data together, the perchlorate feature “does seem to kind of disappear, which is concerning.”
That doesn’t necessarily mean the perchlorates aren’t there, though, she says — they may just be harder to recognize. Hanley and her colleagues are working on a more reliable way to identify similar salts on Mars based on several lines of evidence, not just a single line in the spectrum.
“We definitely know that these salts are on the surface of Mars,” Hanley says. “They could still be important for habitability. But we have to be more cautious about detecting them.”
Also see: Geophysical Research Letters, Challenges in the Search for Perchlorate and Other Hydrated Minerals With 2.1‐μm Absorptions on Mars
E. K. Leask B. L. Ehlmann M. M. Dundar S. L. Murchie F. P. Seelos
09 November 2018
Did the Viking probes detect life?
The two Viking Mars landers each carried four types of biological experiments to the surface of Mars in the late 1970s. These were the first Mars landers to carry out experiments to look for biosignatures of microbial life on Mars. …The Labeled Release (LR) experiment is the one that gave the most promise for the exobiologists…. Initially, according to a 1976 paper by Levin and Patricia Ann Straat the results were inconclusive [no life discovered]
…In a 2002 paper published by Joseph Miller, he speculates that recorded delays in the system’s chemical reactions point to biological activity similar to the circadian rhythm previously observed in terrestrial cyanobacteria.
In April 2012, an international team including Levin and Straat published a peer reviewed paper suggesting the detection of “extant microbial life on Mars”, based on mathematical speculation through cluster analysis of the Labeled Release experiments of the 1976 Viking Mission.
Life on Mars Found by NASA’s Viking Mission? New analysis suggests robots discovered microbes in 1976. Ker Than, National Geographic News