The Microbes of Mars

Scientists are working to determine if microbes can survive on Mars — and if so, what the best habitats on the Red Planet may be.
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Space agencies have long prioritized preventing contamination over our hunt for life on Mars. Now is the time to reassess and update this strategy — before human beings get there and inevitably introduce Earth organisms despite our best efforts. The worry is that, otherwise, terrestrial invaders could jeopardize potential Mars life. They carried out specific biological experiments looking for evidence of microbial life.

Life on Mars is possible after scientists find bacteria flourishing in driest place on Earth

Even worse, if a dedicated life-seeking spacecraft ever does get to Mars, planetary protection policies will allow it to search for life everywhere on the Martian surface, except in the very places we suspect life may exist: The concern is that exploration could contaminate them with terrestrial microorganisms. Consider again the Europeans who first journeyed to the New World and back. Yes, smallpox and syphilis traveled with them, between human populations, living inside warm bodies in temperate latitudes. But that situation is irrelevant to Mars exploration. A more accurate analogy would be bringing 12 Asian tropical parrots to the Venezuelan rainforest.

In 10 years we may very likely have an invasion of Asian parrots in South America.

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Microorganisms on Earth have evolved to thrive in challenging environments like salt crusts in the Atacama desert or hydrothermal vents on the deep ocean floor. So if Earth life cannot survive and, most importantly, reproduce on Mars, concerns going forward about our spacecraft contaminating Mars with terrestrial organisms are unwarranted.

This would be the parrots-in-Antarctica scenario. On the other hand, perhaps Earth microorganisms can, in fact, survive and create active microbial ecosystems on present-day Mars — the parrots-in-South America scenario. We can then presume that terrestrial microorganisms are already there, carried by any one of the dozens of spacecraft sent from Earth in the last decades, or by the natural exchange of rocks pulled out from one planet by a meteoritic impact and transported to the other. The cleaning procedures we use on our robots rely on pretty much the same stresses prevailing on the Martian surface: They end up killing only those microorganisms with no chance of surviving on Mars anyway.

So current cleaning protocols are essentially conducting an artificial selection experiment, with the result that we carry to Mars only the most hardy microorganisms. This should put into question the whole cleaning procedure. Further, technology has advanced enough that distinguishing between Earthlings and Martians is no longer a problem. If Martian life is biochemically similar to Earth life, we could sequence genomes of any organisms located. And if it is different, we would be able to identify such differences based on its building blocks. On Earth, perchlorates also act as an energy source for some microorganisms.

As it turned out, when bathed in UV light, these salts can actually be lethal. When Wadsworth and her advisor exposed the soil bacterium Bacillus subtilis to perchlorates while irradiating the cells with UV levels typical for the Martian surface, the microbes died within minutes.

Deep below the surface, UV and ionizing radiation are significantly reduced, while pressure and temperature begin to increase. Analysis of the sediments also points to once-habitable conditions, with evidence of simple organic molecules that may have originated from biological sources. Data gathered from the crater by rovers and orbiters have revealed evidence both of past and possibly present water and of simple organic molecules—two essential ingredients for life.

Recently, while examining data collected by the rover Curiosity , a group of researchers discovered boron, a chemical element that can stabilize the sugars used to make RNA Geophys Res Lett , Some scientists believe that this element may have even contributed to the origin of life on Earth.

Scientists currently only have speculative estimates about when the Red Planet was last amenable to life.

Life on Mars - Wikipedia

For example, NASA researcher Alfonso Davila and his colleagues have proposed that parts of Mars may have been habitable as recently as 5 million to 10 million Earth years ago Astrobiology , They estimate that during that period, the planet was tilted at an angle that may have provided polar regions with enough solar energy to melt the subsurface ice. After completing additional analyses, the researchers also posited that the water composition in the atmosphere during these periods was similar to that seen in the driest parts of the Atacama Desert in Chile, where microbes have been found living in extremely arid soil Astrobiology , Of course, the most definitive way to confirm life on Mars would be to collect live or previously living specimens.

ExoMars , a rover that the European Space Agency plans to send to Mars in , will be equipped with a drill that can extract soil samples from depths down to two meters, the deepest of any Mars sampling to date. Without knowing exactly what life-forms, if any, exist on our red, dusty neighbor, it is difficult to predict what people might encounter when they eventually get there.

Water marks

Directly probing for life on the Red Planet takes some finesse, as scientists must ensure that they do not accidently misidentify organisms that hitched a ride from Earth as Martian. Although it is not possible to reduce the risk of contamination to zero, researchers can take measures to lower the chances that they will introduce Earthly organisms into their experiments. Curiosity , for example, is barred from exploring the RSLs, due to concerns that the rover, which was not completely sterilized prior to launch, might contaminate the suspected water in those regions.


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The evidence is piling up that if we want to find these signs of life on Mars, we really need to get down below the surface to get away from nasty oxidants and environmental influences. Future rovers will be subjected to various sterilization strategies before launch, including wiping down surfaces with sterilizing solutions, baking heat-resistant components at high temperatures, and using highly sensitive biosensors to identify the presence of microbes.

Researchers are also trying to ensure that the human explorers NASA plans to send to Mars by the s do not contaminate the planet—a much more difficult task, as most of the methods used to clean spacecraft cannot be applied to people. Monitoring microbial migrants within astronaut communities is also important for managing human health. Keeping any potential life-forms native to Mars from hitching a ride back to Earth is another concern.

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Scientists and policy makers want to ensure that samples brought back by rovers or human explorers—or living organisms that accidently hitch a ride—will not endanger species on Earth. But big questions remain about the plausibility and safety of such missions. People who land on the Red Planet will face harsh conditions, such as frigid temperatures, low pressure, and an atmosphere with precious little oxygen. Micron-size dust particles may also be a major factor, as they could cause respiratory problems and contain toxic materials.

In addition, Martian soil contains abundant amounts of perchlorates, a type of salt that can impair the functioning of the human thyroid, which could be hazardous to scientists digging in the dirt. On the other hand, perchlorates might actually be extremely useful during a mission to the Red Planet. Not only are they a component of rocket fuel, the compounds could also be a source of oxygen for human consumption: A much more serious concern about living on Mars is radiation. Without a protective magnetic field like that surrounding the Earth, the surface of the Red Planet is constantly bombarded with galactic cosmic rays—high-energy particles from space that can lead to a variety of health problems.

At the doses of cosmic radiation that humans would receive on a trip to the Red Planet, one of the primary problems they will face is cancer. The cancer risk is slightly higher in women because they have the added concerns of breast and ovarian cancer plus a greater risk of developing lung cancer, although the latter association is not well understood, Cucinotta says. Radiation exposure can also alter the tumor microenvironment in ways that promote cancer.

Using mouse models of breast cancer, Mary Helen Barcellos-Hoff , a radiation oncologist at the University of California, San Francisco, and her colleagues discovered that when healthy epithelial cells were transplanted into an animal that had been exposed to Mars-like radiation, tumors developed from those unirradiated cells Cancer Cell , More recently, scientists have amassed evidence suggesting that cosmic radiation may have worrisome effects on the brain.

Specifically, Charles Limoli of the University of California, Irvine, and colleagues have shown in animal experiments, mostly with rodents, that these galactic particles can cause deficits in learning and memory, reduce the complexity and density of dendritic spines, and lead to persistent neuroinflammation Sci Adv , 1: