Ewao Content Uploads 2016 Mars Presence Life
(Phys.org)—In 1976, two Viking landers became the beginning The states spacecraft from Earth to touch downwards on Mars. They took the first high-resolution images of the planet, surveyed the planet's geographical features, and analyzed the geological composition of the temper and surface. Perhaps nearly intriguingly, they also performed experiments that searched for signs of microbial life in Martian soil.
Overall, these life-detection experiments produced surprising and contradictory results. I experiment, the Labeled Release (LR) experiment, showed that the Martian soil tested positive for metabolism—a sign that, on Earth, would almost certainly suggest the presence of life. However, a related experiment institute no trace of organic fabric, suggesting the absence of life. With no organic substances, what could be, or seem to be, metabolizing?
In the forty years since these experiments, scientists have been unable to reconcile the alien results, and the general consensus is that the Viking landers found no conclusive evidence of life on Mars. Nonetheless, a minor minority of scientists argues that the Viking results were positive for life on Mars.
One prominent proponent of this view is Gilbert Levin, Experimenter of the Viking LR experiment. At kickoff, Levin idea that the LR results were unclear, and stated merely that the results were consistent with biology. However, in 1997, later many years of farther experiments on Earth, along with new discoveries on Mars (which NASA has at present alleged "habitable"), and the discovery of microorganisms living under conditions on Earth as astringent as those on Mars, he and his Viking Co-Experimenter, Dr. Patricia A. Straat, have argued that the Mars results are best explained past living organisms.
Recently, Levin and Straat published a perspective piece in the journal Astrobiology in which they reconsider the results of the Viking LR experiment in low-cal of recent findings on Mars and contempo proposals for inorganic substances that may mimic the observed metabolism-like processes. They contend that none of the proposed abiotic substances sufficiently explains the Viking results, and that Martian microbes should all the same be considered every bit the best explanation of the results.
How the Labeled Release experiment worked
In the LR experiment, both the Viking 1 and Viking 2 landers collected samples of Martian soil, injected them with a drop of dilute food solution, and then monitored the air above the soil for signs of metabolic byproducts. Since the nutrients were tagged with radioactive carbon-14, if microorganisms in the soil metabolized the nutrients, they would be expected to produce radioactive byproducts, such every bit radioactive carbon dioxide or methyl hydride.
Before launching the Viking spacecraft, the researchers tested the experimental protocol on a wide variety of terrestrial soils from harsh environments, from Death Valley to Antarctica. In each case, the experiments tested positive for life. And so as a control, the researchers heated the samples to 160 °C to kill all lifeforms, and then retested. In each example, the experiments now tested negative. To further confirm that the experimental procedure would non produce false positives, the researchers tested it on soils known to be sterile, such as those from the Moon and the Surtsey volcanic island nigh Iceland, which produced negative results as expected.
Once on Mars, the LR experiment was performed after the experiment searching for organic molecules came up empty-handed. And then it came as a surprise when both Viking landers, located 4,000 miles apart, collected soil that tested positive for metabolism. To dominion out the possibility that the strong ultraviolet radiation on Mars might be causing the positive results, the landers collected soil buried underneath a rock, which again tested positive. The command tests also worked, with the 160 °C sterilization control yielding negative results.
In addition, information technology seemed that whatsoever was doing the metabolizing was relatively fragile, since metabolic activity was significantly reduced when heating the sample to l °C, and completely absent when storing the soil in the night for two months at ten °C. Levin and Straat believe that these results provide some of the strongest evidence that the soil contained Martian life.
Nonbiological candidates
Always since the LR experiments, researchers have been searching for other kinds of nonbiological chemicals that might produce identical results.
In their new paper, Levin and Straat review some of these proposals. I possible candidate is formate, which is a component of formic acrid found naturally on Earth. A 2003 LR-type experiment establish that formate in a soil sample from the Atacama Desert in Due south America produced a positive result, even though the soil contained about no microorganisms. However, the study did not include a sterilization control, and it'due south probable that the formate concentration in the Atacama Desert is much higher than that on Mars.
Another potential candidate is perchlorate or 1 of its breakup products. In 2009, the Phoenix mission to Mars detected perchlorates in the Martian soil. Although perchlorates could yield a positive result because they produce gas when interacting with some amino acids, they practice not pause down at 160 °C, and so would continue to requite positive results later on the sterilization control.
A 2013 study proposed that cosmic rays and solar radiation can cause perchlorate to pause downward into hypochlorite, which would produce positive results and, different perchlorate, is destroyed by heating at 160 °C. For these reasons, hypochlorite is arguably the best candidate nonetheless to explain the LR results.
Nevertheless, Levin and Straat note that hypochlorite has not yet been tested at 50 °C (the temperature at which the activity of the Martian soil was significantly reduced) or after long-term storage in the dark (which produced a negative issue for the Martian samples). And so at this point, no nonbiological agent has satisfied all of the LR results.
Biological candidates
Today researchers know much more about Mars than they did twoscore years ago. 1 of the biggest discoveries came in 2014, when the Mars Science Laboratory Curiosity rover detected the presence of organic molecules on Mars for the offset time.
Over the by 2 years, Marvel'due south onboard Sample Analysis at Mars (SAM) laboratory has detected methane, chlorinated hydrocarbons, and other organic molecules. Researchers suspect that these organic substances may have formed on Mars or been carried there by meteorites.
The discovery of organic matter on Mars raises the question of why the Viking experiment did not detect organic matter dorsum in 1976. As Levin explains, at that place are multiple reasons that might explain why the Viking results were negative.
"We long ago pointed out the problems with the Viking GCMS (gas chromatograph—mass spectrometer)," Levin said. "Even its experimenter, Dr. Klaus Biemann, oftentimes stressed that the GCMS was not a life-detection experiment. It required at least one meg microbial cells to detect any organic thing. In add-on, the instrument had frequently failed when tested on Globe. Later, information technology was claimed that perchlorate in the soil destroyed the organic matter. All the same, I view this cautiously as at that place is no bear witness for perchlorate at the Viking sites."
In light of the recent findings, Levin and Straat believe that it'due south important to reconsider the LR results every bit having a biological origin. Other researchers who support this view have proposed that Martian life could take the form of methanogens (microorganisms that produce methane as a byproduct), halophiles (which tin can tolerate high salt concentrations also as severe radiation and low oxygen concentrations), or some type of "cryptobiotic" microorganism that lies dormant until reactivated, such every bit by a nutrient solution like the 1 in the LR experiment.
Publishing challenges
Publishing a newspaper about life on Mars was very different than publishing more typical studies (over the years, Levin'southward research has included depression-calorie sweeteners, pharmaceutical drugs, safer pesticides, and wastewater treatment processes, amongst others). Information technology took nigh 20 years for Levin and Straat to publish a peer-reviewed newspaper on their interpretation of the Viking LR results.
"Since I first ended that the LR had detected life (in 1997), major juried journals had refused our publications," Levin told Phys.org. "I and my co-Experimenter, Dr. Patricia Ann Straat, then published mainly in the astrobiology section of the SPIE Proceedings, afterwards presenting the papers at the annual SPIE conventions. Though these were invited papers, they were largely ignored past the bulk of astrobiologists in their publications." These papers are available at gillevin.com.
"At a meeting of the Canadian Infinite Bureau, I met Dr. Sherry Cady, the editor of Astrobiology. She invited me to submit a paper for peer review. I did and information technology was promptly bounced, not even sent out for review because of its life claim.
"Pat and I decided nosotros would produce a paper that would withstand the utmost scientific scrutiny. It took years of countless renditions and compliance with or explanation away of a myriad of reviewers' comments, but we persisted until we disposed of every adverse annotate. Thus, we call back this publication is quite significant in that information technology was scrubbed so thoroughly that the points remaining are firmly established.
"You may not agree with the conclusion, but you cannot disparage the steps leading at that place. Yous tin say only that the steps are insufficient. But, to us, that seems a tenuous defense, since no 1 would abnegate these results had they been obtained on Earth."
Futurity outlook
For Levin and Straat, i of the most important reasons for considering the beingness of life on Mars is a practical 1 that may touch on hereafter enquiry.
"It seems prudent that the scientific community maintain biology equally a viable explanation of the LR experimental results," they write in their paper. "It seems inevitable that astronauts will eventually explore Mars. In the interest of their health and safety, biology should be held in the forefront of possible explanations for the LR results."
Going forward, Levin and Straat propose that carefully designed experiments tin can help to answer the question of the beingness of life on Mars. In particular, LR-type experiments that test for chiral preference could tell whether the metabolizing substance is biological or chemical, since only biological agents can distinguish between left and right isomers. The scientists also emphasize the importance of the continued search for organic molecules, peculiarly those with biological significance such every bit amino acids, unproblematic carbohydrates, lipids, proteins, and DNA. Futurity experiments may also provide the possibility of examining Martian soil under a microscope.
Despite the positive outlook, Levin and Straat note that all hereafter experiments volition have an unavoidable drawback: the potential for contamination by previous landers. In this regard, the Viking landers were unique in that they were the merely pristine Martian life-detection experiment that we will ever have.
More than information: Gilbert V. Levin and Patricia Ann Straat. "The Case for Extant Life on Mars and Its Possible Detection by the Viking Labeled Release Experiment." Astrobiology. October 2016, xvi(10): 798-810. DOI: 10.1089/ast.2015.1464
© 2016 Phys.org
Citation: Did forty-yr-former Viking experiment find life on Mars? (2016, October 21) retrieved 13 April 2022 from https://phys.org/news/2016-x-year-old-viking-life-mars.html
This document is subject to copyright. Autonomously from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for data purposes but.
Source: https://phys.org/news/2016-10-year-old-viking-life-mars.html
0 Response to "Ewao Content Uploads 2016 Mars Presence Life"
Enviar um comentário