Space telescope discovery raises prospect of mini solar systems

LOS ANGELES (AP) - NASA's Spitzer Space Telescope has spotted a dusty disc of material around a very small "failed star" called a brown dwarf, raising the possibility that there may be miniature solar systems in which planets orbit objects not much larger than planets, scientists said Monday.

The brown dwarf named OTS 44 is only about 15 times the mass of Jupiter, much smaller than any other brown dwarf known to be surrounded by a disc of planet-building material, said Kevin Luhman, lead author of a study by the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

"The neat thing about this brown dwarf is that it's near the dividing line between what's considered brown dwarf masses and planetary masses," Luhman said in a teleconference from the meeting on planet formation and detection at the Aspen (Colo.) Winter Conference on Astrophysics.

"This raises the possibility that there could be out there in space, objects that have planetary masses ... that themselves have planetary companions around them," he said, noting that the objects could be as small as five times the mass of Jupiter.

Early in their lives, stars like the sun were surrounded by discs of material from which planets like Earth formed.

Brown dwarfs are star-like objects with masses less than one-tenth the mass of the sun, Luhman said. Although they probably formed in the same way as stars, brown dwarfs are not massive enough to ignite and don't shine. Mostly dark, they are sometimes called failed stars.

OTS 44, located about 500 light-years from Earth in the constellation Chamaeleon, was found last year by the researchers using the Gemini Observatory in Chile. They then used Spitzer, an infrared telescope, to spot the glow of its disc.

Before the discovery, the smallest brown dwarf known to have such a disc was 25 to 30 times the mass of Jupiter.

"We have identified the smallest body that is known to have the building blocks around it for making planets," Luhman said.

Astronomer Giovanni Fazio, a study co-author from the Harvard-Smithsonian Center, said in a statement that the results raised a "tantalizing possibility" that planets may form around objects with planet-scale masses.

Fazio led the development of Spitzer's infrared array camera at NASA's Goddard Space Flight Center in Greenbelt, Md.

The research will be published in the Feb. 10th issue of The Astrophysical Journal Letters. Other authors include Paola D'Alessia of the Universidad Nacional Autonoma de Mexico, and Nuria Calvet, Lori Allen, Lee Hartmann, Thomas Megeath and Philip Myers of the Harvard-Smithsonian Center for Astrophysics.

Spitzer, a $670 million mission launched in August 2003, is managed by NASA's Jet Propulsion Laboratory in Pasadena, Calif. Science operations are conducted by the Spitzer Science Center at the California Institute of Technology.

I wonder if it's possible a planet in orbit about a brown dwarf could be habitable. It would have to be very close, maybe orbiting just a few hundred miles from it. I wonder if brown dwarfs are stable and not subject to flares.

It's actually very possible, brown dwarfs give off most of their heat as infra-red and tidal warming of a planetary size satellite's core could keep it habitable year round. It would always be night and the Gas giant would hang huge in the sky, blood red and warm.

Also consider that the moon would most likely be tide locked revolving that close (up to 100,000 miles) to the brown dwarf.

Caption: Artist's Impression of the brown dwarf Gl 229B (with the low mass star Gl 229A) sitting about 40 AU away. This brown dwarf is a few billion years old, with a surface temperature of about 1000K. Its mass is in the 30-50 jupiter mass range (or 3-5% of our Sun). The dull red color is what your eye would see, there is more luminosity coming out in the near infrared. The dark bands are hypothetical; although dust does form in the atmospheres of brown dwarfs, it is unclear how non-uniform their appearance is. The banding is reasonable, since they usually rotate very fast (in hours; like Jupiter). A couple of magnetic "spots" are also shown; there is evidence of magnetic fields at least on the younger brown dwarfs (although it doesn't give rise to the same atmospheric heating and activity as on stars). Gl 229B is about 100,000 times fainter than our Sun (and almost 1000 times fainter than its low mass stellar companion).

These substellar objects were first conceived of in the early 1960s as "failed stars". Stellar models suggested that a true star must have a mass at least 80 times that of Jupiter to kindle the stable fusion of hydrogen (this limit is currently thought to be about 75 jupiters). Objects with less mass were believed to exist, but it was recognized that they would be extremely difficult to find because they would be quite low in luminosity, and emit very little visible light. For that reason, they can be viewed as a constituent of baryonic "dark matter". Indeed, we currently have a hard time directly seeing an old brown dwarf beyond 100 pc. After 20 years of searching and false starts, the first confirmed brown dwarfs were announced in 1995. This was due to a combination of increased sensitivity, better search strategies, and new means of distinguishing substellar from stellar objects. Since then, a great deal of progress has been made on the observational front. We are now in a position to say a substantial amount about actual brown dwarfs. We have a rough idea of how many of them occur as solitary objects and how many are found in binary systems. We have obtained the first glimpse of atmospheres intermediate in temperature between stars and planets, in which dust formation is a crucial process. This has led to the proposal of the first new spectral classes in several decades, and the need for new diagnostics for classification and setting the temperature scale. The first hints on the substellar mass function are in hand, although all current masses depend on models. It appears that numerically, brown dwarfs may well be as common as stars (though they appear not to contain a dynamically interesting amount of mass).

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