Earth-like planets as common as fleas?

by Molly Bentley on November 8, 2010

by Seth Shostak

It’s been 15 years since Swiss astronomers announced the first discovery of a world around another normal star – the celebrated planet known (to astronomers, at least) as 51 Peg b.

This planet was like a puppy on your doorstep: thoroughly appealing, but totally unexpected. It spun around its home star in only 4 days, and weighed in at half the mass of Jupiter (or more). In their wildest imaginings, astronomers had never anticipated that a planet would hug its sun as tightly as would an Italian mother.

Today, the tally of confirmed extrasolar planets is a hair shy of 500. Of these, about two-thirds are heavy-duty worlds, as massive as 51 Peg b or more. The general assumption is that these big guys are mostly so-called “gas giants,” planets similar to Jupiter and Saturn, wrapped in thick, smelly atmospheres. This preponderance of giants [find synonym] has caused some people to worry that our own solar system, with its retinue of small, rocky worlds, is unusual. In that case – if Earth-like worlds are really rare – then complex life might be rare too.

Well, strike that concern from your worry list. Two weeks ago, a group of astronomers led by Andrew Howard at the University of California at Berkeley have done a careful study of nearby stars using the Keck telescope on Hawaii’s Big Island. Their conclusion is that about one-fourth of all stars like the Sun (or somewhat dimmer) have close-in planets that are approximately the same size as Earth. One-fourth!

By extrapolating their results, they estimate that NASA’s Kepler mission will find between 120 and 260 Earth-size worlds when data acquisition is complete in another two years. That’s roughly ten times as many as the Kepler team itself is expecting.

Bottom line? Earth-size worlds may be as common as fleas at a pound. And for those looking for life elsewhere, that’s good news.

{ 4 comments… read them below or add one }

avatar Steve Bergman November 9, 2010 at 7:40 pm

That’s nice to hear. Though I guess I’m wondering how a project using terrestrial telescopes, and presumably the wobble method, can predict what Kepler with find. I suppose the phrase “or somewhat dimmer” must be key. Extrapolation from an M-Dwarf survey?

That said, the Kepler folks aren’t all that pessimistic. Didn’t Natalie Batalha, Kepler team member, say in “Formula One: The Drake Equation”, that they expected to find along the lines of 50 to 100 Earth-like planets? And that they would only be catching about 0.4% of any Earth-like planets which exist in their sample? (1/2% * 0.75)

Then again, I have a better feeling about the M-Dwarf systems, anyway. With those, we can find “Earths” which are closer than what Kepler is designed to do. And once JWST is up, the possibilities for study of those nearer “Earths” orbiting relatively dim stars are well beyond what I ever expected to see in my lifetime.

-Steve Bergman

avatar Andrew Planet November 10, 2010 at 8:14 pm

The best synonym for giant planets that I have found is Jovian planets

Andrew Planet

avatar Andrew Planet November 10, 2010 at 8:16 pm

Perhaps exojovian planets would be a more precise term?

avatar Cindy November 19, 2010 at 12:53 am

This is quite a remarkable discovery!

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