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 discovery of flowing water on Mars: 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 on Mars?
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
After running Viking’s LR data through a mathematical test designed to separate biological signals from non-biological signals, Miller’s team believes that the LR experiments did indeed find signs of microbial life in Martian soil.
[…They] used a technique called cluster analysis, which groups together similar-looking data sets. “We just plugged all the [Viking experimental and control] data in and said, Let the cluster analysis sort it,” Miller said. “What happened was, we found two clusters: One cluster constituted the two active experiments on Viking and the other cluster was the five control experiments.”…
The team concedes, however, that this finding by itself isn’t enough to prove that there’s life on Mars. “It just says there’s a big difference between the active experiments and the controls, and that Viking’s active experiments sorted with terrestrial biology and the controls sorted with non-biological phenomena,” Miller said.
Still, the new findings are consistent with a previous study published by Miller, in which his team found signs of a Martian circadian rhythm in the Viking LR experiment results. Circadian rhythms are internal clocks found in every known life-form—including microbes—that help control biological processes… On Earth this clock is set to a 24-hour cycle, but on Mars it would be about 24.7 hours—the length of a Martian day.
In his previous work, Miller noticed that the LR experiment’s radiation measurements varied with the time of day on Mars. “If you look closely, you could see that the [radioactive-gas measurement] was going up during the day and coming down at night. … The oscillations had a period of 24.66 hours just about on the nose,” Miller said. “That is basically a circadian rhythm, and we think circadian rhythms are a good signal for life.
Gilbert V. Levin, 10/10/2019, Scientific American
… I was fortunate to have participated in that historic adventure as experimenter of the Labeled Release (LR) life detection experiment on NASA’s spectacular Viking mission to Mars in 1976.
On July 30, 1976, the LR returned its initial results from Mars. Amazingly, they were positive. As the experiment progressed, a total of four positive results, supported by five varied controls, streamed down from the twin Viking spacecraft landed some 4,000 miles apart.
The data curves signaled the detection of microbial respiration on the Red Planet. The curves from Mars were similar to those produced by LR tests of soils on Earth. It seemed we had answered that ultimate question.
When the Viking Molecular Analysis Experiment failed to detect organic matter, the essence of life, however, NASA concluded that the LR had found a substance mimicking life, but not life.
Inexplicably, over the 43 years since Viking, none of NASA’s subsequent Mars landers has carried a life detection instrument to follow up on these exciting results. Instead the agency launched a series of missions to Mars to determine whether there was ever a habitat suitable for life and, if so, eventually to bring samples to Earth for biological examination.
… Life on Mars seemed a long shot. On the other hand, it would take a near miracle for Mars to be sterile. NASA scientist Chris McKay once said that Mars and Earth have been “swapping spit” for billions of years, meaning that, when either planet is hit by comets or large meteorites, some ejecta shoot into space. A tiny fraction of this material eventually lands on the other planet, perhaps infecting it with microbiological hitch-hikers.
That some Earth microbial species could survive the Martian environment has been demonstrated in many laboratories. There are even reports of the survival of microorganisms exposed to naked space outside the International Space Station (ISS)….
… The Viking LR sought to detect and monitor ongoing metabolism, a very simple and fail-proof indicator of living microorganisms. Several thousand runs were made, both before and after Viking, with terrestrial soils and microbial cultures, both in the laboratory and in extreme natural environments. No false positive or false negative result was ever obtained. This strongly supports the reliability of the LR Mars data, even though their interpretation is debated….
In her recent book To Mars with Love, my LR co-experimenter Patricia Ann Straat provides much of the scientific detail of the Viking LR at lay level. Scientific papers published about the LR are available on my Web site.
In addition to the direct evidence for life on Mars obtained by the Viking LR, evidence supportive of, or consistent with, extant microbial life on Mars has been obtained by Viking, subsequent missions to Mars, and discoveries on Earth:
- Surface water sufficient to sustain microorganisms was found on Mars by Viking, Pathfinder, Phoenix and Curiosity;
- Ultraviolet (UV) activation of the Martian surface material did not, as initially proposed, cause the LR reaction: a sample taken from under a UV-shielding rock was as LR-active as surface samples;
- Complex organics, have been reported on Mars by Curiosity’s scientists, possibly including kerogen, which could be of biological origin;
- Phoenix and Curiosity found evidence that the ancient Martian environment may have been habitable.
- The excess of carbon-13 over carbon-12 in the Martian atmosphere is indicative of biological activity, which prefers ingesting the latter;
- The Martian atmosphere is in disequilibrium: its CO2 should long ago have been converted to CO by the sun’s UV light; thus the CO2 is being regenerated, possibly by microorganisms as on Earth;
- Terrestrial microorganisms have survived in outer space outside the ISS;
- Ejecta containing viable microbes have likely been arriving on Mars from Earth;
- Methane has been measured in the Martian atmosphere; microbial methanogens could be the source;
- The rapid disappearance of methane from the Martian atmosphere requires a sink, possibly supplied by methanotrophs that could co-exist with methanogens on the Martian surface;
- Ghost-like moving lights, resembling will-O’-the-wisps on Earth that are formed by spontaneous ignition of methane, have been video-recorded on the Martian surface;
- Formaldehyde and ammonia, each possibly indicative of biology, are claimed to be in the Martian atmosphere;
- An independent complexity analysis of the positive LR signal identified it as biological;
- Six-channel spectral analyses by Viking’s imaging system found terrestrial lichen and green patches on Mars rocks to have the identical color, saturation, hue and intensity;
- A wormlike feature was in an image taken by Curiosity;
- Large structures resembling terrestrial stromatolites (formed by microorganisms) were found by Curiosity; a statistical analysis of their complex features showed less than a 0.04 percent probability that the similarity was caused by chance alone;
- No factor inimical to life has been found on Mars.
In summary, we have: positive results from a widely-used microbiological test; supportive responses from strong and varied controls; duplication of the LR results at each of the two Viking sites; replication of the experiment at the two sites; and the failure over 43 years of any experiment or theory to provide a definitive nonbiological explanation of the Viking LR results.
What is the evidence against the possibility of life on Mars? The astonishing fact is that there is none. Furthermore, laboratory studies have shown that some terrestrial microorganisms could survive and grow on Mars.
NASA has already announced that its 2020 Mars lander will not contain a life-detection test. In keeping with well-established scientific protocol, I believe an effort should be made to put life detection experiments on the next Mars mission possible. I and my co-experimenter have formally and informally proposed that the LR experiment, amended with an ability to detect chiral metabolism, be sent to Mars to confirm the existence of life: non-biological chemical reactions do not distinguish between “left-handed” and “right-handed” organic molecules, but all living things do.
… Moreover, the Chiral LR (CLR) could confirm and extend the Viking LR findings. It could determine whether any life detected were similar to ours, or whether there was a separate genesis. This would be a fundamental scientific discovery in its own right. A small, lightweight CLR has already been designed and its principle verified by tests. It could readily be turned into a flight instrument.