The project, called Systemic, enlists volunteers to help astronomers better understand what kinds of planetary systems inhabit our galaxy, the Milky Way, and whether systems like our solar system are common. Astronomers have already found nearly 200 extrasolar planets orbiting other stars. But according to Gregory Laughlin, associate professor of astronomy and astrophysics at UCSC, the types of planetary systems astronomers are finding may not represent the full range of what is out there.

"There are interesting and profound selection effects in the data," said Laughlin, who started the Systemic project with a small group of collaborators.

The technique most often used to find extrasolar planets relies on measuring slight wobbles in a star's motion caused by the gravitational tug of an orbiting planet. This technique favors configurations in which the orbiting planet is not only large, like Jupiter, but also close to the star. As a result, these so-called "hot Jupiters" are overrepresented in the current census of extrasolar planets.

Other potential biases arise from factors that limit how observations are made. Astronomers are often limited to blocks of telescope time lasting only a few days, which means they cannot observe prospective planetary systems as often as they would like. The limited geographic locations of telescopes also limit what parts of the sky astronomers can observe. As a result of these kinds of restrictions, some planetary systems are studied more than others, and so the current data on extrasolar planets does not yet fully reflect what is really out there, Laughlin said.

To get a better handle on these problems, Laughlin and his collaborators launched the Systemic project, in which public participation will help create a virtual database of extrasolar planetary systems. His team includes Aaron Wolf, who developed the Systemic software as a UCSC undergraduate; graduate student Stefano Meschiari; postdoctoral researcher Eugenio Rivera; and Paul Shankland at the U.S. Naval Observatory.

Laughlin said he was inspired by the success of public participation in other scientific research projects, such as SETI@home, where users download a screensaver that uses their personal computer's processing power to analyze radio telescope data. He wanted to do something similar that would further stir public interest in astronomy. Instead of just a screensaver, however, he wanted something that also engaged the user.

"We wanted to involve the public in a meaningful way," Laughlin said.

The project involves a sophisticated simulation of the search for planets. The researchers created a data set of 100,000 stars, complete with many diverse planetary systems. Participants can analyze this virtual galaxy with software available on the project web site (http://oklo.org). Using the software, volunteers can analyze the data for a target star, varying planetary properties like mass, orbital shape, and period to find a configuration that best fits the data. The web site includes a tutorial on the software, called the Systemic Console, as well as a blog, which Laughlin updates regularly.

The simulated search uses the same kind of planetary wobble data that astronomers measure, and it also incorporates all the observational biases they encounter when collecting real data. What the public provides is a set of simulated observations the researchers can compare with observations in the real world. No one knows how extrasolar planets are distributed in the Milky Way, but the researchers know the full range of planetary systems in the simulated virtual galaxy. By comparing the simulated observations with the real observations, the researchers hope to better understand how well, or how poorly, the search process collects a census of extrasolar planets.

"How good are we at detecting strange systems? Stars with three planets instead of two? Two instead of one? There are a lot of questions like this that can be addressed with a large-scale simulation," Laughlin said.

And because it is a large-scale simulation, the participation of the public is critical. Complicated systems with multiple planets require a human eye and patience to arrive at an accurate description. It is a time-consuming process that involves a lot of data.

"We need public participation because the most interesting systems are very hard to decipher," said Laughlin. "Automated methods often fail to adequately describe them."

Recruiting the public to do astronomical research is not new to Laughlin, who helped start the Transitsearch project (http://www.transitsearch.org/). Transitsearch asked amateur astronomers to point their telescopes at potential extrasolar systems and to search for events called transits, when a planet passes in front of its star, slightly dimming the starlight. Astronomers can learn about the size, composition, and atmosphere of the planet just from the dimming of the light. Of course, Transitsearch requires participants to have telescopes and cameras. Systemic invites public participation without the need for expensive equipment.

Systemic is now in an introductory phase to develop a reliable user base. The first of the virtual data will not be released for another month. Meanwhile, scientists have released real data of extrasolar systems for people to analyze. Sky and Telescope magazine is sponsoring a contest in which participants race to find the best configuration of a planetary system, with a new set of data every two weeks. Winners receive a star atlas.

Although the project started in January, the software and the web site were not available until two months ago. So far, several hundred people have already volunteered and are producing good results, Laughlin said. In some cases, he said, volunteers have found better descriptions of planetary systems than the astronomers.

While users have come from all walks of life, educators and students form a major market for Systemic. The web site already receives 800 unique hits a day, Laughlin said. Eventually, he hopes to reach 10,000 users.

"I think it's realistic because the Internet is a global thing. We have users from all over the world," he said.

As computers become more powerful in the coming decades, the researchers hope to go beyond virtual data of planetary systems. Laughlin said he envisions creating entire virtual worlds that people can explore and that remain true to the laws of physics.

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