In a new paper published in the journal Life, Prof Dirk Schulze-Makuch of Washington State University and his colleagues from Germany draw upon what is known about Earth’s most extreme lifeforms and the environments of Mars and Saturn’s largest moon, Titan, to paint a picture of what alien life could be like.
The young Mars would have had enough water to cover its entire surface in a liquid layer about 140 m deep, but it is more likely that the liquid would have pooled to form an ocean occupying almost half of Mars’s northern hemisphere, and in some regions reaching depths greater than 1.6 km. Image credit: M. Kornmesser / ESO / N. Risinger, skysurvey.org.
Earth life, with its unique biochemical toolset, could feasibly survive on a terrestrial, Mars-type planet with a few novel adaptations.
“First, organisms would need a way to get water in an environment that is akin to a drier and much colder version of Chile’s Atacama Desert. A possible adaptation would be to use a water-hydrogen peroxide mixture rather than water as an intracellular liquid,” Prof Schulze-Makuch said.
“For example, on our planet, a species of beetle called bombardier excretes an explosive mix of hydrogen peroxide and other chemicals to ward off predators. On other planets, under gravity conditions similar to those present on Mars, a bombardier beetle-like alien could excrete a similar reaction to propel itself as much as 300 meters into the air.”
Hydrogen peroxide is a natural antifreeze that would help microorganisms survive frigid Martian winters. It is also hygroscopic, meaning it naturally attracts water molecules from the atmosphere.
During the daytime, plant-like microorganisms on a Martian-like surface could photosynthesize hydrogen peroxide.
At night, when the atmosphere is relatively humid, they could use their stored hydrogen peroxide to scavenge water from the atmosphere, similar to how microbial communities in the Atacama use the moisture that salt brine extracts from the air to stay alive.
“A larger, more complex alien creature, maybe resembling Earth’s bombardier beetle, could use these microorganisms as a source of food and water. To move from one isolated patch of life-sustaining microorganisms to another, it could use rocket propulsion,” Prof Schulze-Makuch said.
If life does exist on Titan or a Titan-like planet elsewhere in the Universe, it uses something other than water as an intracellular liquid.
This image is a composite of several images taken during two separate Titan flybys in 2006. The large circular feature near the center of Titan’s disk may be the remnant of a very old impact basin. The mountain ranges to the southeast of the circular feature, and the long dark, linear feature to the northwest of the old impact scar may have resulted from tectonic activity on Titan caused by the energy released when the impact occurred. Image credit: NASA/JPL/University of Arizona.
“One possibility is a liquid hydrocarbon like methane or ethane. Non-water based lifeforms could feasibly live in the liquid methane and ethane lakes and seas that make up a large portion of Titan’s surface, just as organisms on Earth live in water,” Prof Schulze-Makuch said.
Such aliens would take in hydrogen in place of oxygen and react it with high energy acetylene in the atmosphere to produce methane instead of carbon dioxide.
Due to their frigid environment, these organisms would have huge and very slowly metabolizing cells.
The slow rate of metabolism would mean evolution and aging would occur much slower than on Earth, possibly raising the life span of individual organisms significantly.
“On Earth, we have only scratched the surface of the physiological options various organisms have. But what we do know is astounding. The possibilities of life elsewhere in the Universe are even more staggering,” Prof Schulze-Makuch said.
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Dirk Schulze-Makuch et al. 2015. The Physical, Chemical and Physiological Limits of Life. Life 5 (3), pp. 1472-1486; doi: 10.3390/life5031472
