exoplanet, courtesy NASA
By James Dacey
One of the many questionable aspects of reported encounters with extraterrestrial beings is that – despite their big deformed heads and stretchy green skin – the aliens always seem to resemble the human form.
Well according to a group of US scientists, the search for habitable planets is also suffering from “little green man” syndrome and we need to re-evaluate the necessities for life in the universe.
Ask any scientist with a passing interest in SETI (the search for extraterrestrial intelligence) and they’ll tell you, scouring the universe for Hollywood’s aliens is a ridiculously blinkered approach. After all, the number of environmental factors that influence which genes combine, and which combinations prosper, is simply unimaginable. That is assuming the aliens would even possess genes as we understand them.
Up until now over 330 planets observed orbiting stars other than our Sun and, after next month, this total may start to increase rapidly as NASA launches its Kepler telescope to search for more “exoplanets”. So far, most exoplanets have been gas giants like Jupiter, but one of Kepler’s goals is to find Earth-sized planets at a “habitable” distance from their parent stars.
The question is, once astrophysicists start to see these Earth-like planets, how will we know if they are harbouring life?
According to Caleb Scharf at Columbia University and his colleagues, our best bet is to look for the signatures of key molecules like H2O and O2. Importantly, they say, this should be done in the context of the overall environmental condition of a planet.
Appreciating the sensitivity, and huge number of parameters, involved in climate systems, Scharf and Co say we need a fundamental modelling hierarchy to help understand terrestrial planet climates, and observables, as needed by astronomers.
They have produced a “White Paper” to act as a central reference point for any scientist interested in interpreting astrophysical data. The proposed “strategy” is built around five central questions:
1. What are the surface and atmospheric conditions?
2. Does the planet represent a plausible environment for life now, in the past, or in the future?
3. What is the overall compositional nature of the planet?
4. Is there evidence for the presence of an active geosphere?
5. Is there evidence for the presence of an active biosphere?
So if you’re an amateur astronomer with an ambition to find the next Earth then download yourself a copy of this White Paper.