bruc%mit-ml@sri-unix.UUCP (07/26/83)
ngement of green colored patches on a Martian roc over the course of a year. The rock must be fairly distant from the lander because its image is only about 10 by 20 pixels. They look like lichens. All very interesting. It's clear we should go back for another look. One interesting speculation that I had about this -- if there is life on Mars, it's quite possible it came from Earth. Since material from Mars is believed to have traveled to the earth and landed in Antarctica (by being blasted from Mars by a meteor impact and eventually intersecting the earth's orbit), the reverse is also possible. I wonder if the spores of ancient microorganisms would be capable of surviving the voyage (suitably encased or shielded by rock)..
HPM@SU-AI@sri-unix.UUCP (08/02/83)
From: Hans Moravec <HPM@SU-AI> n533 0224 02 Aug 83 BC-MARS-3takes-08-02 By David L. Chandler (c) 1983 Boston Globe (Independent Press Service) Seven years ago in July, a remote-controlled machine about the size of a VW Rabbit separated itself from an orbiting spacecraft and descended to a red, rocky plain. It was the Viking 1 lander, first object from Earth ever to land on Mars. One of its primary goals was to search for signs of life, using a set of three biological experiments. Yet seven years after that first Viking landing, the debate rages on: Did the tests show signs of life, or just a puzzling set of chemical reactions? Some scientists say there's strong, convincing evidence for life, while others are positive that Mars is barren. The issue is not likely to be resolved until - and unless - there's another Mars mission. But those who think that life is likely got a significant boost recently when tests done on Antarctic soil were found to duplicate the most puzzling of the results from Mars. Both sets of tests showed evidence of microbial life, in the form of ''respiration'' of gases from the soil, and yet showed no sign of life's basic building blocks - organic compounds - within that soil. In short, there is now direct evidence that life forms can exist in soil without producing enough chemical debris - enough dead bodies - to be detected by the Viking equipment; that, as one scientist put it, there can be music even though there's no sign of any instruments. By resolving the biggest apparent conflict in the Mars data, this finding has moved some disbelievers into the ''maybe'' camp. But many still feel that life is unlikely on Mars. Klaus Biemann, the scientist at Massachusetts Institute of Technology who developed the Viking test for organic compounds in the soil, says ''the majority of scientists, both in and out of the Viking team, believe that the biology experiments were negative, and that they can all be explained by one non-biological chemical reaction or another.'' Norman Horowitz, a Cal-Tech biochemist who designed one of Viking's life-detection tests, has put it even more strongly. Writing about the results of the mission in Scientific American, he said: ''At least those areas on Mars examined by the two spacecraft are not habitats of life.'' On the other hand, biochemist Alexander Rich of MIT, who was also a member of the Viking biology team, said recently: ''It is not correct to say that Mars has been shown to be lifeless. We failed to demonstrate that life is there, but we didn't disprove it. It's a matter of judgment. It certainly warrants going back with a broader set of experiments to see what's there.'' Probably the strongest believer in the evidence for life on Mars is Gilbert Levin, president of Biospherics Inc. of Maryland. He was the chief scientist in charge of the Viking life-detection experiment that gave the clearest positive results, and he says that ''If you look objectively at the data, it's more likely than not that we discovered life. ''People think the Viking tests failed to return any evidence for life,'' says Levin. ''But in fact, there's a lot of evidence.'' Levin thinks that his experiment, the ''labeled release'' (LR) test, produced strong evidence for the existence of some kind of microbes - perhaps resembling Earth bacteria or algae - by measuring carbon-dioxide discharges from soil that had been moistened with a nutrient solution. Levin also has discovered that there are greenish patches visible on rock surfaces in the Viking photographs, which he thinks might turn out to be a form of life similar to lichens - one of the hardiest of living organisms. And other recent discoveries have also boosted the prospects for Martian life, prompting Rich, the MIT biochemist, to say, ''I think the conclusions are vastly different than they were before.'' The announcement this year of the discovery of microbes that survive at over 500 degrees F. near ocean-floor thermal vents shows that ''Life is really much more adaptive than we had anticipated,'' says Rich. ''That discovery showed that life can adapt to extremely high temperature and pressure, so we shouldn't write off Venus (as a possible habitat for life). I believe this shows that life can adapt to low temperature and pressure as well.'' On Mars, temperatures seldom rise above freezing, and the atmospheric pressure is less than one-hundredth of Earth's. As for interpreting the Viking results, Levin points out that despite intensive efforts over the last seven years, no one has yet come up with a specific set of chemical reactions that can explain the results of his LR experiment on Mars. If no chemical explanation can be found, scientists agree, a biological reaction - living microorganisms in the Martian soil - would be the only way to account for the data. The results of Levin's test did in fact meet all the criteria established before the mission to conclude that life had been discovered. First, a substantial positive response - consisting of a release of gas (probably carbon dioxide) from the soil, as would be expected from the metabolism of microorganisms such as bacteria or algae - was obtained from each ''active'' run of the experiment in two different regions of the Martian surface. And second, the biological nature of the response was apparently confirmed by the negative results - virtually no gases produced - from each ''control'' run, in which the soil was first sterilized by heat. The control runs were considered a crucial test for determining whether a response really came from living organisms, since microbes would be killed by the high temperature and so stop ''breathing,'' whereas most non-living chemical reactions would not be affected by the heat. As Viking chief biologist Harold Klein pointed out in his official summary of the biology test results, ''The LR .-.-. yielded data which met the criteria originally developed for a positive. On this basis alone, the conclusion would have to be drawn that metabolizing organisms were indeed present in all samples tested.'' Since the test met the requirements for a ''presumptive positive,'' why didn't the scientists announce that life had been discovered? And why do they still disagree on what the results mean? Levin claims with some annoyance that his fellow scientists ''changed the rules after the results were in. If we had followed the rules, we would have stood up and said: 'We discovered life.'-'' There were, however, three unexpected aspects of the data that caused most of the scientists to hold back from saying that the results indicated life in the Martian soil. One was the fact that the LR test result, although positive, was very different from the usual response seen in Earth soils: Instead of the rate of gas production increasing steadily because the microorganisms multiplied rapidly in the soil, as happens when Earth soil is tested, the Mars response gradually leveled off. Biochemist Cyril Ponnamperuma, editor of the respected scientific journal Origins of Life, says that because of this leveling off of the response, the positive result is ''not completely convincing, but it is tantalizing.'' Another problem was the strange response from another life-detection test, the Gas-Exchange experiment, which produced an intense, sudden burst of oxygen when the Martian soil was exposed to moisture. This result, which everyone agreed looked like a non-living chemical reaction rather than a lifelike response, suggested to most of the scientists that there was some kind of highly reactive chemical compound in the soil, and that perhaps the same compound was responsible for the LR response. But by far the greatest stumbling block for a biological interpretation of the Mars data was the resoundingly negative, and totally unexpected, result of a test called the GCMS (gas chromatograph-mass spectrometer). This experiment searched for the presence in Martian soil of organic (carbon-based) chemicals - the compounds from which life is made, though they also occur naturally even in the depths of space. Most people had expected the exact reverse of the results that were found: That there would be plenty of organics in the soil, but no reaction from the life tests. A positive life-test result with no organics seemed impossible, so there was considerable consternation when the data came in and showed just that. But this apparent conflict has now been resolved, claims Levin. Looking back through published reports on the development of the experiments used in the Viking mission, he found that a sample of soil preserved in NASA laboratories, which had been collected from a dry valley in Antarctica (the environment on Earth that comes closest to duplicating present Martian temperatures and lack of moisture), had been tested by both the GCMS and the much more sensitive LR test. The results of these two independent tests very closely duplicated the results from Mars. The tests showed that the soil, Antarctic soil number 726, which contained a small quantity of living cells, had no organic chemicals detectable by the GCMS, yet gave a clearly positive result on the LR test. The seeming discrepancy was apparently nothing more than a difference in the sensitivity levels of the two tests, says Levin. So the Martian results of those two experiments, which many biologists thought were seriously contradictory, have now been demonstrated to be perfectly compatible. Biochemist Ponnamperuma was one of those who thought the conflicting results of these two tests made it very unlikely that they indicated life on Mars. But when asked last week about Levin's report on the Antarctic soil, Ponnamperuma exclaimed, ''It's hard to fight that. To me, that says that it's an open question again.'' In addition to the positive LR test results, another bit of evidence for Martian life that Levin has discovered is that, contrary to the first reports from the Viking imaging team, the surface seen in the photographs of the Martian landscape is not uniformly red. In fact, there are small greenish patches on some of the rocks and on the soil. These patches have changed shape and position over the course of a Martian year (about two Earth years), and they appear to match quite closely the appearance, color, and thickness of terrestrial lichens, long thought to be the form of Earth life best adapted for survival in the cold, dry Martian climate. Levin points out that lichens are the pioneers of life on Earth, the first living things to appear on barren rocks. His analysis of the color and the changing shapes of the patches on Mars has since been confirmed by other NASA scientists. With so many signs pointing toward at least a possibility of current life on Mars, why do most scientists continue to speak so negatively about that possibility? Levin thinks his colleagues are afraid that ''If we're proven wrong by the next lander, we'll look foolish.'' But to Levin, the reverse seems at least as likely: ''It reminds me of the emperor's clothes. If it does turn out that there are organisms on Mars, people will say 'couldn't these people see?'-'' But there is at least one area of agreement among all those involved in the Viking mission. As Rich puts it, ''Scientists are not unanimous about the interpretation of the results - we disagree on details - but we are all in agreement that we have to go back and do a more comprehensive set of tests. ''If we proved that there was life there, it would be one of the great cultural events of this age. The scientific fallout, of course, would be considerable. If we found another biological system on another planetary body, my God, there are an infinite number of questions we could ask. But perhaps the most important thing is that whenever we address cosmic questions like this, all of a sudden we see much more clearly that we - Homo sapiens - really are all one.'' END nyt-08-02-83 0533edt ***************