The textbook account of where planetary systems come from--namely, disks of dust and gas that encircle stars--may require an addendum. Researchers have found that comparable disks girdle distant exoplanets far less massive than our sun. The discovery raises the possibility that these planetary mass objects, or planemos, are orbited by other planets and moons--like our own solar system, but smaller.

Astronomer Ray Jayawardhana of the University of Toronto and his international team of colleagues surveyed in two studies the optical spectra of seven exoplanets: One study focused on six planemos that float freely through space without a specific relationship to a star. The other looked at an exoplanet locked in a binary system with a failed star whose mass is just 8 percent that of our sun. The exoplanets in both studies bore the infrared emissions associated with dusty disks. "At least in two of the planemos we see possible evidence that they are accreting material from their disk," Jayawardhana adds. "It's spiraling in to the objects, very similar to young stars."

Such disks are thought to spawn stars and satellites over time as the material collides and agglomerates. Planemos may originate in the same way--by the gravitational collapse of gas and dust. "Nature is probably making these extremely low mass things in the same way that it made the sun," Jaywardhana says. Of course, low mass is relative; the smallest of the planemos is still five times the size of Jupiter, which is more than 300 times as massive as Earth. Jupiter's largest moons probably arose from one of these disks, according to Jayawardhana. "The diversity of worlds out there is truly remarkable," he notes. Both studies were presented yesterday at the 208th meeting of the American Astronomical Society in Calgary.