Two Penn State astronomers presented information earlier this month at the American Astronomical Society's annual meeting that could help in the discovery of new planets outside our solar system.

Steinn Sigurdsson, professor of astronomy and astrophysics and John Debes, (graduate-astronomy and astrophysics), began working together last spring to develop ways of identifying planets around stars that had evolved into white dwarves. The two are hopeful that their research will help lead to the discovery of planets that will sustain life.

"The basic problem is to understand how many planets there are out there," Sigurdsson said. "And what sorts of planets there are."

According to NASA, a white dwarf is the result of a dying star that has exhausted all its nuclear fuel. They are typically the size of the earth with a mass half that of the sun, making them extremely dense.

Current technology used to discover planets is biased, Sigurdsson said, because astronomers tend to look for planets where they believe they will find them. Sigurdsson compared the problem to a drunken person looking for lost car keys.

"He'll always look for them under a street light," Sigurdsson said.

Their research began as a thought exercise about what happens to a solar system after a sun dies, Sigurdsson said. They considered the chaos in a system whose star is dying; orbits of planets in the system change, comets enter into regions they were not found before and planets collide, forming new planets.

At the AAS conference Debes and Sigurdsson suggested searching around white dwarves would be useful because they are dimmer and smaller. Trying to find planets around a normal sun is much more difficult in comparison.

"Its kind of like looking for a quarter next to a search light," Debes said.

In particular, finding newly formed planets next to a white dwarf using infrared technology would be easier because new planets are much warmer and brighter.

Using a computer simulation, Debes was able to describe what happens to two planets, relatively near each other, after a star becomes a white dwarf.

He used three stages in the simulation, beginning with the planets revolving around a normal star. Gradually, he reduced the size of the star and observed what happened to the planets. He found the planets began interacting with each other causing drastic changes in their orbits.

Eventually the force between the interacting planets was great enough that one planet was kicked out of the system completely.

Debes and Sigurdsson said comet clouds comparable to our solar system's Oort cloud could be disrupted when a planet is flung out of its orbit around a white dwarf. This would result in debris moving in closer to the dwarf star.

Normally, the area around a dwarf star is free of dust and debris, because during its phase as a red giant, the star expands enough so that the heat effectively cleans out the surrounding regions of the star. Dust around a white dwarf suggests the possibility of a planet being in the system.

"If there is a connection between dusty white dwarves, we could use that as a flag," Debes said. "That white dwarf may have planets."

As many 3,000 people viewed the information at the AAS conference held Washington, D.C.

Debes said many scientists took an interest in what they presented.

In the future, Sigurdsson and Debes would like to do more simulations to contribute to their hypotheses.

The ability to complete the simulations on computers enables astronomers to make more insightful predictions and could also lead to the discovery of things they had not predicted, Sigurdsson said.

One such prediction, Sigurdsson said, is an explanation for why nebulae from dead stars all have different shapes. It could be that if there is a large Jupiter-sized planet in the system that survived the star's death, it could be carving into the nebulae producing the strange shape.

No modeling has been done for this, Sigurdsson said, but it is an example of another way the scientists' current simulations could be used.

"We've basically just done a big thought experiment," Sigurdsson said. "Nothing we've done is real, quote unquote."