In All The Galaxy, Just 15 Percent Of Solar Systems Are Like Ours

Jan 05, 2010 by Pam Frost Gorder

(PhysOrg.com) -- In their quest to find solar systems analogous to ours, astronomers have determined how common our solar system is.

They've concluded that about 10 percent of in the universe host systems of like our own, with several gas giant planets in the outer part of the .

"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."

Gaudi will report the results of the new study on Tuesday, January 5 at the American Astronomical Society Meeting in Washington, DC, when he accepts the Helen B. Warner Prize for Astronomy.

The find comes from a worldwide collaboration headquartered at Ohio State called the Microlensing Follow-Up Network (MicroFUN), which searches the sky for .

MicroFUN astronomers use a method called gravitational microlensing, which occurs when one star happens to cross in front of another as seen from Earth. The nearer star magnifies the light from the more distant star like a lens. If planets are orbiting the lens star, they boost the magnification briefly as they pass by.

This method is especially good at detecting giant planets in the outer reaches of solar systems -- planets analogous to our own Jupiter.

This latest MicroFUN result is the culmination of 10 years' work -- and one sudden epiphany, explained Gaudi and Andrew Gould, professor of astronomy at Ohio State.

Ten years ago, Gaudi wrote his doctoral thesis on a method for calculating the likelihood that extrasolar planets exist. At the time, he concluded that less than 45 percent of stars could harbor a configuration similar to our own solar system.

Then, in December of 2009, Gould was examining a newly discovered planet with Cheongho Han of the Institute for Astrophysics at Chungbuk National University in Korea. The two were reviewing the range of properties among extrasolar planets discovered so far, when Gould saw a pattern.

"Basically, I realized that the answer was in Scott's thesis from 10 years ago," Gould said. "Using the last four years of MicroFUN data, we could add a few robust assumptions to his calculations, and we could now say how common planet systems are in the universe."

The find boils down to a statistical analysis: in the last four years, the MicroFUN survey has discovered only one solar system like our own -- a system with two gas giants resembling Jupiter and Saturn, which astronomers discovered in 2006 and reported in the journal Science in 2008.

"We've only found this one system, and we should have found about eight by now -- if every star had a solar system like Earth's," Gaudi said.

The slow rate of discovery makes sense if only a small number of systems -- around 10 percent -- are like ours, they determined.

"While it is true that this initial determination is based on just one solar system and our final number could change a lot, this study shows that we can begin to make this measurement with the experiments we are doing today," Gaudi added.

As to the possibility of life as we know it existing elsewhere in the , scientists will now be able to make a rough guess based on how many solar systems are like our own.

Our solar system may be a minority, but Gould said that the outcome of the study is actually positive.

"With billions of stars out there, even narrowing the odds to 10 percent leaves a few hundred million systems that might be like ours," he said.

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User comments : 3

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Nik_2213
2 / 5 (1) Jan 06, 2010
How does this tie in with recent finding that (based on initial sample) extra-solar planets and low-lithium in their stars seem to go together ??
Phelankell
3.5 / 5 (2) Jan 06, 2010
This is still very hypothetical. There are far too many assumptions involved to make a percentage figure accurate by any means. Especially when we look at other figures for the rarity of non-cluster single star systems, then the relative rarity of Earth sized planets on an inner system orbit, coupled with the lack of cold gas giant planets we've found.

Basically you can't read the first page of War and Peace and understand the entire book.
statueofmike
not rated yet Jan 07, 2010
"Just" 15%?

I'm sorry, princess. I don't know what fancy Galaxies you've been living in, to be so disappointed. We'll try to accommodate you.

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