Dim sun. A dusty disk girdles a young brown dwarf with just 15 times Jupiter's mass, in this artist's conception. Such disks now appear common, even around the smallest dwarfs.

Solar System Lite

When nature creates stars, it swaddles them in disklike clouds of dust that may someday coalesce into planets. According to two new studies, such clouds also arise around the failed stars known as brown dwarfs--even ones as small as giant planets. The results tantalize astronomers with the prospect that objects not much larger than Jupiter could host planets of their own.

The findings are gaining notice this week at the Planet Formation and Detection conference in Aspen, Colorado, where astronomers have gathered to mark the first decade of extrasolar planet hunting. During that decade, finding flattened disks of gas and dust around young stars became as routine as finding planets around mature stars. And in the past several years, disks seemed equally likely around brown dwarfs: gaseous balls less than 75 times the mass of Jupiter, unable to ignite sustained hydrogen fusion.

Now, satellite and telescope observations are sensitive enough to discern whether the puniest dwarfs also sport disks. A team led by astronomer Kevin Luhman of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts, found extra emissions of infrared light from a faint dwarf with just 15 times Jupiter's mass--at the threshold of what astronomers consider "planetary mass." The faint glow is a telltale sign of dust warmed by the young dwarf's heat, Luhman says. NASA's Spitzer Space Telescope revealed the disk's imprint in a mere 20 seconds.

Another team used ground-based telescopes to look for radiation from gas and dust spiraling onto dozens of brown dwarfs and low-mass stars--the largest such survey conducted to date. Of the newest dwarfs, which formed only about a million years ago, at least half actively accumulate matter that falls from the inner parts of disks, says study co-author Ray Jayawardhana of the University of Toronto in Ontario, Canada. This mirrors the pattern that astronomers see in young, full-fledged stars, he says, where astronomers see evidence that embryonic planets clear out gaps in dusty disks. "Objects with disks span the entire range from a few times the mass of our sun to 15 times the mass of Jupiter," Jayawardhana says. "The infancies of brown dwarfs are remarkably similar to the infancies of young, sunlike stars."

Indeed, the similarities prompt speculation that mini-disks could yield mini-systems of planets. Little brown dwarfs probably have less than one Jupiter's worth of mass in their disks, says CfA astronomer Charles Lada. That's not enough for big gassy planets, but rocky or icy Earths might assemble, he believes.

Related sites
Planet Formation and Detection conference
Spitzer Space Telescope
Gibor Basri's brown dwarf page at UC Berkeley

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