Early Returns From Galactic Census: Not As Many Planets as Expected

"Plenty of Solar Systems Like Ours Expected "
Space.com (January 5, 2010)

"There's good news and bad news.

"The bad news is that solar systems like ours are in the minority in the Milky Way. The good news is that's still an awful lot of potential twins out there.

"Combining the results of a search for extrasolar planets in our galaxy and a method for calculating the likelihood that extrasolar planets exist, only about 15 percent of the stars in the Milky Way likely host systems of planets like our own, one astronomer said here today at the 215th meeting of the American Astronomical Society.

" 'Now we know our place in the universe,' said Ohio State University astronomer Scott Gaudi. 'Solar systems like our own are not rare, but we're not in the majority, either.'

"The speculation came partially from an exoplanet-hunting effort called the Microlensing Follow-up Network (MicroFUN). MicroFUN uses a method called gravitational microlensing, which occurs when one star crosses in front of another from the perspective of Earth...."

If 'only' 15 % of the Milky Way galaxy's 200,000,000,000 to 400,000,000,000 stars have planets, that's 30,000,000,000 to 60,000,000,000 stars with planets sharing the galaxy with us.

That's a whole lot of zeroes.

And, as the Space.com article discusses, astronomer Gaudi's speculation and others are just that: speculations.

But, with hundreds of planets already spotted around other stars, they're informed speculations.

The phrase "like ours" isn't all that well defined. It could mean a star with a handful of rock planets orbiting nearby, with a few gas giants on longer orbits. Or, something else.

One point I found interesting was that there's a possibility that our Solar system has more than the average number of planets.

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Related posts, at

• "A Serious Search for Other Worlds, Life, and - Maybe - Extra-Terrestrial Intelligence"