Looking for Life

We know life.  Just look around, it’s everywhere!

Living things tend to consume other living or once-living things to live. That stuff gets metabolized, broken down into life-force producing molecules.  It boils down to energy.  Energy is the life-force produced via metabolic processes.

If you’re searching for life, let’s say on a planet 5 light-years away it isn’t practical to look for life-force. On Earth most life provides us with hints, sometimes face-slaps of its presence, in the form of metabolic by-product gasses.  Bean burritos come to mind as a face-slap example.  The carbs, fat and protein in those beans are metabolized by your gut bacteria, spewing copious and varied gasses in the process.  You know what happens next.

If it were that simple, and who knows, it might sometimes be that simple.  But, even at a reasonably close 5 light-years, a planet teaming with life will be challenging to recognize.  Unless of course we pick up top 40 hit radio signals.  So, how do astronomers (astrobiologists) think they will find signs of life on extrasolar planets?

Most all life forms produce some metabolic products, and gas is not the only one.  Living things also might excrete solid products that can accumulate to form structures.  Living things, at least larger ones on Earth also build structures. These things are all called biosignatures.  Right now, our best bet for detecting life out there is via detecting their biosignature(s).  The kicker, we really do not know exactly what biosignatures extrasolar organisms produce.  Another kicker, many apparent biosignatures can be created through processes not associated with life (abiotic)!  Astrobiologists have a major challenge ahead.

At light-year distances spotting physical structures is out of the question with current technology, so the focus is on gasses.  How do you identify gasses in a planet’s atmosphere at light-year distances? Absorption spectroscopy.  This is done by “reading” a planet’s atmosphere with a spectroscopic telescope as it passes in front of its host star.  That spectrum is then compared with the host star’s spectrum.  Differences in their spectra can indicated specific elements/molecules in the planet’s atmosphere.  A big challenge is our lack of high temperature/pressure spectrographic experience, like that expected from many exoplanets.  Astrobiologists are developing databases of molecular spectrographic signatures from high temperature and pressure experiments.

Another challenge, under certain conditions a gas might appear to be a different gas.  Witness the gas phosphine, reportedly found at high altitude in Venus’s clouds.  On Earth it is produced by anaerobic microorganism metabolism and has no known abiotic way to form.  Could there be bacteria living high up in the Venusian atmosphere?  Maybe.  Or it could be simple sulfur dioxide whose spectrographic properties have been modified by local conditions (temperature and pressure).

After all this, finding and verifying biosignatures is just the starting point.  Then the real work begins.

What’s in the Sky?

May 15&16; dusk; west:  A waxing crescent Moon and Mars are close.