Search for Alien Life Should Include Exotic Possibilities

“For most researchers’ money, an Earth-like planet is the best bet for finding alien life. But looking in such an exclusive range of possibilities might give them only half the story.

A team of scientists is now proposing an index that ranks a planet’s habitability using a much wider set of criteria.

“We are trying not to be geocentric, calculating planetary habitability independent of liquid water,” said physicist Abel Mendez of the University of Puerto Rico in Arecibo and one of the co-authors of the new index, published in Astrobiology on Nov. 21.

Astronomers have discovered more than 700 extrasolar planets, many of them gas giants that orbit too near or far from their parent star to be comparable to Earth. But Mendez and his group want to expand the narrow possibilities generally considered necessary for a planet to host life.

The team proposes to rank planets on both an Earth Similarity Index (ESI) and also a broader Planetary Habitability Index (PHI). The first index looks at how close a planet is to Earth in mass, temperature, and composition while the second is based on the whether or not it possesses more exotic chemistries, liquids, and energy sources than found on our planet. Alien life could be based on elements other than carbon, require liquids other than water, and gain energy through means other than sunlight.” (via Wired.com).