Planet Clumps and Crystals around Brown Dwarfs
This artist's concept shows microscopic crystals in the dusty disk
surrounding a brown dwarf, or "failed star." The crystals, made up of a
green mineral found on Earth called olivine, are thought to help seed the
formation of planets.
NASA's Spitzer Space Telescope detected the tiny crystals circling around
five brown dwarfs, the cooler and smaller cousins of stars. Though
crystallized minerals have been seen in space before -- in comets and
around other stars -- the discovery represents the first time the little
gem-like particles have been spotted around confirmed brown dwarfs.
Astronomers believe planets form out of disks of dust that circle young
brown dwarfs and stars. Over time, the various minerals making up the
disks crystallize and begin to clump together. Eventually, the clumps
collide and stick, building up mass like snowmen until planets are born.
About the Graph: Planet Clumps and Crystals around Brown Dwarfs
The graph of data from NASA's Spitzer Space Telescope shows the spectra
(middle four lines) of dusty disks around four brown dwarfs, or "failed
stars," located 520 light-years away in the Chamaeleon constellation. The
data suggest that the dust in these disks is crystallizing and clumping
together in what may be the birth of planets.
Spectra are created by breaking light apart into its basic components,
like a prism turning sunlight into a rainbow. Their bumps represent the
"fingerprints" or signatures of different minerals.
Here, the light green vertical bands highlight the spectral fingerprints
of crystals made up primarily of a green silicate mineral found on Earth
called olivine. As the graph illustrates, three of the four brown dwarfs
possess these microscopic gem-like particles. For comparison, the spectra
of dust between stars (top) and the comet Hale-Bopp (bottom) are shown.
The comet has the tiny crystals, whereas the interstellar dust does not.
The broadening of these spectral features or bumps -- seen here as you
move down the graph - indicates silicate grains of increasing size.
Another analysis of this same data shows that some of the brown dwarfs'
dusty disks flare in their outer regions, while others are flattened.
This flattening is correlated with increasing grain size, and probably
occurs because the heavier dust grains are settling downward.
Together, these observations - of crystals, growing dust grains and
flattened disks - provide strong evidence that the dust around these
brown dwarfs is evolving into what might become planets. Prior to the
findings, these first steps of planet formation were seen only in disks
around stars, the brighter and bigger cousins to brown dwarfs.