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A University of Arizona planetary scientist who correctly predicted the discovery of a "missing planet" in a distant solar system said he expects the proof will help make the search for other exoplanets more efficient.

The discovery of another planet in the HD 74156 solar system was the result of noticing that distant system didn't fit the pattern of other known star and planet systems, said Rory Barnes, a postdoctoral research associate in the UA's Lunar and Planetary Laboratory.

Essentially, Barnes said, of the handful of known solar systems, all the others fit the same pattern of star and planet groupings. He said there appears to be a delicate balance between stars and the number and spacing of planets.

When systems get too closely packed, Barnes said — so close that their gravitational effect on one another is greater than their star's gravitational pull — one can "slingshot" the other right out of the solar system.

So far, Barnes said, there is no conclusive evidence of this having happened. But that is something else that may yet be proved.

Barnes, who got an undergraduate degree in astronomy from the UA, was a graduate student at the University of Washington when he and two other UW scientists developed the Packed Planetary Systems method for predicting planet locations between 2002 and 2004.

Their prediction was confirmed last year when a team from the University of Texas discovered a planet in the location predicted by Barnes, Sean Raymond and Thomas Quinn.

Barnes said the discoverers of the missing planet — HD 74156D — weren't aware of his prediction, nor was he aware of their discovery, until he read about it in a scientific journal in September.

He spoke about the Packed Planetary System hypothesis and the specific prediction Wednesday at the annual meeting of the American Astronomical Society in Austin.

"I don't really feel like I'm saying, 'I told you so,' " Barnes said, referring to his presentation.

He said he sees the predictive powers of the packed-planets model to be significant mostly because it will allow a more systematic search for exoplanets.

"In the past, people were sort of looking for planets haphazardly," Barnes said.

And with billions of stars that could be home to planets — maybe one much like ours — he said it is helpful to have a hint when one goes hunting.