In the latest example of the apparent fecundity of nature, a tiny starlike object too small to be a star seems to be surrounded by a tiny disk of dust that could someday form planets, which could perhaps even be briefly capable of supporting life, according to observations.
The discovery raises the possibility that astronomers will soon discover actual planets and habitable abodes around objects that are barely larger than planets themselves. The starlike body, only about 15 times as massive as the planet Jupiter, is the smallest object yet to be found with such a disk. With a temperature of 3,600 degrees Fahrenheit, it is also the coolest. As such, the object is not really a star at all, but a failed star known as a brown dwarf that is only barely bigger than the largest giant planets.
"It's just incredible," said Kevin Luhman of the Harvard-Smithsonian Center for Astrophysics. "A little disk that could form planets around an object that is small enough itself to be a planet." Luhman led an international team of astronomers that observed the brown dwarf, known as OTS 44, using the Spitzer Space Telescope. He will be discussing his results this week at a meeting on extraterrestrial planets at the Aspen Center for Physics in Colorado. A paper describing the results will be published in The Astrophysical Journal Letters.
Geoffrey W. Marcy of the University of California, Berkeley, said the report opened a new possible abode for life, on Earth-like planets orbiting brown dwarfs. "While these earths would be warmed up for only a few million years," he said in an e-mail message, "it is interesting to imagine what biochemistry might flicker valiantly during that brief period when the brown dwarf is luminous enough to warm up the earth, only to freeze over before Darwinian evolution can kick in."
The work continues a recent trend in which astronomers using bigger and bigger telescopes have shifted their attention somewhat, from the biggest and brightest objects in the cosmos--supernova explosions, quasars and giant galaxies--to the smallest and dimmest. Little dim things far outnumber their more striking and violent cousins, and it is among these humbler denizens of the cosmos that astronomers must look for life and life-friendly conditions.
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The Spitzer Space Telescope, launched into orbit around the Sun in 2003, is the fourth and last of NASA's so-called Great Observatories. It is designed to see the , or heat radiation emitted by celestial objects.
Cool dim objects like small stars, brown dwarfs and planets emit electromagnetic radiation most strongly in infrared wavelengths, which are longer than those of visible light, and which can pass through interstellar dust clouds that often shroud new stars, but Earth's atmosphere blocks infrared light. And so prospective infrared astronomers have had to go to space, starting with the Infrared Astronomical Satellite, IRAS, in 1983, which discovered disks of dust around several stars, including Vega.
Since then, disks have been detected or have been inferred to exist around thousands of stars, including a few brown dwarfs. In December, astronomers using Spitzer announced that they had detected the