Sunday, February 1, 2009

Life in Distant Places

Alien life is the science fiction writer’s stock in trade.

For whatever reason, humans appear to be very lonely upon this water-drenched, biologically rich, warm, and pleasantly hospitable planet. Much money, time and energy has been invested in SETI programs to discover distant alien civilizations. Unfortunately these technological analogs of ourselves either do not exist or are reluctant to talk (or indicate their existence) to us, their neighbors. Considering humanity’s blood drenched and competitive past, there may be some wisdom in this reluctance.

Lacking communion with the stars, we have turned our attention with some desperation to neighboring worlds. Enceladus, a moon of Saturn, exhibits warm water geysers jetting from fissures near its south poles, suggesting a possible favorable environment for microbial life. Water is a key requisite for life and apparently Europe, a moon of Jupiter, possesses a planet-wide ocean capped by a thick cap of ice. A hopeful theory is that life could have developed on the sea floor around black smoker geysers that spew out superheated water and minerals, similar to those found Earth’s deep sea. The sun plays no part in this existence, the organisms are nourished by sulphur and metallic compounds dissolved in the super-heated water spewing from the vents in the sea floor. This may be an environment in which primitive unicellular organisms, called extremophiles, might have developed. One is tempted to speculate that with enough time and resources this life could have developed a certain amount of complexity, including bioluminescence, as in my fanciful illustration below.

As for the hope of finding life beyond the Earth, Mars wears the crown. From Percival Lowell’s canals and Ray Bradbury’s dying civilizations, Mars has provided a fertile field for science fiction’s speculations. The discovery of water-modified sediments by the Mars rovers and ice by the recent Polar Lander keeps hope alive.

But the best evidence for possible life now springs from observations of methane emissions from specific areas of the Martian surface that vary by seasons.

Methane production can be a byproduct of endolithic life processes, or the result of mineral reactions.

An "endolith" is a microorganism that
colonizes the interior of any kind of rock. Endoliths exist by feeding on traces of iron, potassium, or sulfur and some live deep in the crust. The Ocean Drilling Program found microscopic trails in basalt from the Atlantic, Indian, and Pacific oceans that contain DNA. Photosynthetic endoliths have also been discovered.

Due to their harsh environment, endoliths exhibit a very slow reproduction cycle, sometimes undergoing cell division only once every hundred years. There is little energy is available for reproduction or growth so they don't. But this inactivity also lets the organisms weather very long ice ages in a dormant state, eventually wakening again to life when the rocks warms.

The majority of endoliths generate organic compounds essential for their every day lives from inorganic matter. Some though have specialized in feeding on their relatives (are we surprised?). Micro-biotopes where different endolithic species live together are called a SLiME (Subsurface Lithotrophic Microbial Ecosystem) – which is not exactly “take me to your leader” material. Curiously, perhaps inspired by watching too many remakes of The Blob, my Hunters of Tharsis series published by Analog in the 1970s also employed a giant unicellular creature lurking in the deep caves of Mars. Whatever, or whoever, it absorbed it opportunistically incorporated their traits and DNA into its own capabilities. And after it ingests a number of human colonists a new race of Martians is born.

Sadly, even if there is microbial life on Mars living deep within the crustal rocks nourished by subsurface melt water rich in sulphur compounds, such life forms will, no doubt, be totally unimpressive to a boots-on-the-ground astronaut explorer.

As for the geologic reasons for the methane on Mars, serpentinization is suggested as the alternate source. This is a low-temperature metamorphic process involving heat and water in which Periodotite rocks are oxidized and hydrolyzed with water into serpentinite. In the process large amounts of water are absorbed into the rock and in the chemical reactions hydrogen gas, sulfates and carbonates are reduced and form methane and hydrogen sulfide. Of course, here’s another glimmer of hope for life, since this hydrogen, methane, and hydrogen sulfide can provide energy sources for chemotroph microorganisms.

Is there any possibility at all for Martian surface life considering the nearly non-existant atmosphere, intense cold, and punishing rain of UV radiation? Perhaps. Dark spots on dunes have been seen in Mars Global Surveyor images taken during 1998 – 1999 of the southern polar region. The spots appear at the beginning of the Martian spring and disappear by the beginning of the winter. A Hungarian team proposes that the spots are colonies of photosynthetic Martian microorganisms, which are dormant (and not visible) beneath the ice cap until Sun returns in early spring and light penetrates the ice. When these microorganisms begin to photosynthesize they heat the surroundings and a tiny chamber of liquid water forms around them. As the surface ice layer thins and melts, the cells dry and turn dark, creating the observed features on the ice. Of course this ice is really, really cold. Dry ice cold! And NASA feels the dark patches are simply basaltic ash fragments that accumulate as a residue due to sublimation of the ice. Only better observations will determine which explanation is the correct one.

Apparently our only planetary neighbors will never be much more sophisticated than the mold we wipe off the grout in our showers. Gort and Klatuu have yet to check in. Still, considering how those movies turned out for us here on Earth, perhaps that’s a good thing.

And my Red-Planet cave-dwelling bug fantasy, tiny and adaptive though he is, will remain just that - fantasy.

1 comment:

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