Readable look at chance of life on other worlds

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Artist's concept of Kepler-16b, the first planet known to definitively orbit two stars. (MCT)

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On a clear night, you can see about 5,000 stars with your naked eye. Many of them are thought to have planets orbiting them, much as Earth orbits our own star, the sun.

Using a variety of techniques, astronomers have detected and catalogued more than 700 of these "exoplanets," planets outside our solar system But the question is, does life as we know it inhabit any of them?

In The Life of Super-Earths, Dimitar Sasselov, a professor of astronomy at Harvard and founder of the Harvard Origins of Life Initiative guides readers through a very readable progression of steps that explore the origin of life on Earth and what conditions life might require on worlds beyond our own.

Sasselov begins by recounting how in 1995, the first extrasolar planet, about the size of Jupiter, was discovered orbiting a star called 51 Pegasi. This spawned a new "space race" to discover Earth's twin as part of a search for "the Other" -- our quest for meaning in the vastness of the universe.

The Life of Super-Earths then proceeds through detailed but simple explanations of how observational astronomy contributes to our understanding of stellar evolution. Sasselov writes passionately about a "transit of Venus" (an actual one, not just the play of the same name) in 2004, and how it showed that detecting a transit of a distant planet in front of its parent star is one way that progress is being made in discovering new worlds.

Even though the light of a distant star is dimmed only by a minuscule amount when a planet passes in front, this dimming can be detected with state-of-the-art scientific instruments.

In fact, because computing power and detection instruments are becoming so common, Sasselov half-jokingly notes that any "would-be astronomer of today can set herself up to find a new planet simply by maxing out a credit card."

However, the most significant scientific advancements are being done by international teams of researchers, often on several different continents, co-operating on the observation and analysis of data obtained from satellites like the Kepler mission that has been finding more and more new exoplanets every month.

Yet, it's super-Earths that Sasselov is most interested in finding. He notes the "Goldilocks Hypothesis," that: "the Earth is just the right size (not too big, not too small) and just the right temperature (not too hot, not too cold) for life to emerge here. Life is a rare thing."

Sasselov says that there must exist in our galaxy, the Milky Way, many planets that are more massive and larger than the Earth, super-Earths with rocks, continents and oceans, and even more stable geologically. The first one of these is known as Gliese 876, found in 2005. It's seven times as massive as the Earth but orbits its star too close to be inhabitable.

Astronomers are currently trying to find a super-Earth so much like our own home that it surely must harbour life. Sasselov notes that our knowledge of galactic evolution has allowed some predictions about how many stars have planets like Earth. The number is astounding: there could be "100 million planets with habitable potential today."

Sasselov is optimistic about the future of life on Earth. Even if a man-made nuclear cataclysm destroys life on the surface, or a large asteroid wipes out human civilization, he says, life on Earth will survive because it is "indestructible."

Not humans, of course, but microbes and other forms of highly adaptive organisms living deep within the planet or the bottom of the ocean will carry on. They are the cousins of those that likely inhabit the millions of super-Earths, somewhere in the cosmos.

That may be comforting, to some of us.

Chris Rutkowski is a Winnipeg cynic and science writer who sees little evidence of intelligent life on Earth.

Republished from the Winnipeg Free Press print edition February 4, 2012 J9