New recipe in the search for alien life
Alien life A new model has been developed to help in the search for life beyond our solar system.
The new two-pronged approach designed by researchers from NASA, the SETI Institute and several universities, attempts to replace Earthling-biased preconceptions of what constitutes conditions for life.
The paper, to be published in the December issue of the journal Astrobiology, proposes a new system for classifying exoplanets (those outside our solar system) using two different indices.
An Earth Similarity Index would categorise a planet based on how similar it is to Earth including its mass, radius and temperature. Under this index, the distant 'Goldilocks' world of Gliese 581g comes close to Earth.
Meanwhile, the Planetary Habitability Index would look at issues such as the presence of a stable substrate, available energy, appropriate chemistry, and the potential for holding a liquid solvent.
The recipe is designed to minimise the biased search for 'life as we know it' and to take into account life that might exist under more exotic conditions, says study author astrobiologist Dr Dirk Schulze-Makuch from Washington State University.
Focusing on Earth-based assumptions about habitability may be too restrictive for capturing the potential variety of life forms that, at least in principle, may exist on other worlds according to the authors.
They say habitability isn't necessarily restricted to water as a solvent or to a planet circling a star.
For example, scientists speculate that hydrocarbon lakes on Saturn's moon Titan could host a different form of life, after studies of hydrocarbon environments on Earth found them habitable in principle.
Schulze-Makuch who has just returned from studying Pitch Lake, a poisonous, asphalt pond on the Caribbean island of Trinidad and Tobago says it demonstrates the wide variety of environments life can exist in.
"This may be Earth-based life but it shows there could be a pathway for a very different type of life using a different biochemistry on other planets," says Schulze-Makuch.
"Theoretically, on Titan for example, being so cold, any organism living there would have a very slow metabolism. Maybe it could live for a million years taking a breath just once a month. For us that would be hard to detect that as life."
Orphan planets wandering free of any host star could likewise conceivably feature conditions suitable for some form of life.
Thousands of new worlds
Astrobiologist Dr Charley Lineweaver from the Australian National University says scientists are being flooded with new detections of exoplanets.
Over 700 have been discovered orbiting stars other than the Sun.
Lineweaver suspects those numbers will swell to the tens of thousands over the next few years.
"How are we going to sort through them and classify them, particularly with respect to the thing we're most interested in ... life?"
But while the new models are useful, there's still a problem because we don't have a good definition of what life actually is, says Lineweaver.
"Living things pass on information about themselves through DNA, but so do viruses and we say it's not life because it can't do anything without a host," he says.
"So there's all kinds of ifs, ands, and buts, when it comes to defining what life actually is."
"It's hard to find something if you don't know what you're looking for."
"Because we don't really know much about the origins of life, we don't know which features are the most important for determining whether you will have life elsewhere," says Lineweaver.