Astonomers find tiny planet orbiting tiny starJune 03, 2008An international team of astronomers led by David Bennett of the University of Notre Dame has discovered an extra-solar planet of about three Earth masses orbiting a star with a mass so low that its core may not be large enough to maintain nuclear reactions. The result was presented Monday (June 2) at the American Astronomical Society annual meeting in St. Louis. The planet, referred to as MOA-2007-BLG-192Lb, establishes a record for the lowest mass planet to orbit a normal star. The star, MOA-2007-BLG-192L, is at a distance of 3,000 light years and the lowest mass host star to have a companion with a planetary mass ratio. The mass of the host is about 6 percent of the mass of the sun. Such a star is called a brown dwarf, because this is slightly below the mass needed to sustain nuclear reactions in the core. But the measurement uncertainty also permits a host mass slightly above 8 percent of a solar mass, which would make MOA-2007-BLG-192L a very low-mass hydrogen burning star. "Our discovery indicates that even the lowest mass stars can host planets," Bennett said. "No planets have previously been found to orbit stars with masses less than about 20 percent of that of the sun, but this finding suggests that we should expect very low-mass stars near the sun to have planets with a mass similar to that of the Earth. This is of particular interest because it may be possible use NASA's planned James Webb Space Telescope to search for signs of life on Earth-mass planets orbiting low-mass stars in the vicinity of the sun."
The discovery of the MOA-2007-BLG-192L star-planet system was made by the Microlensing Observations in Astrophysics (MOA), which includes Bennett, and the Optical Gravitational Lensing Experiment (OGLE) collaborations using the gravitational microlensing method. Gravitational microlensing takes advantage of the fact that light is bent as the rays pass close to a massive object, like a star. The gravity from the mass of the intervening object, or lens star, warps surrounding space and acts like a giant magnifying glass. As predicted by Albert Einstein and later confirmed, this phenomena causes an apparent brightening of the light from a background "source" star. The effect is seen only if the astronomer's telescope lies in almost perfect alignment with the source star and the lens star. Astronomers are then able to detect planets orbiting the lens star if the light from the background star also is warped by one or more planets. The primary challenge of the microlensing method is the precise alignments needed for the planetary microlensing signals are quite rare and brief, often lasting less than a day. This discovery was made possible by the new MOA-II telescope at New Zealand's Mt. John Observatory, using the MOA-cam3 camera, which is able to image an area of sky 13 times larger than the area of the full moon in a single image. "The new MOA telescope-camera system allows us to monitor virtually all of the known microlensing events for planetary signals," Bennett said. "We would not have made this discovery without it." The microlensing observations provided evidence that the host star has a mass of about 6 percent of the mass of the sun. This was confirmed by high angular resolution adaptive optics images with the Very Large Telescope (VLT) at the European Southern Observatory in Chile. These images confirm that the planetary host is either a brown dwarf or a very low-mass star. The planet orbits its host star or brown dwarf with an orbital radius similar to that of Venus. But the host is likely to be between 3,000 and 1 million times fainter than the sun, so the top of the planet's atmosphere is likely to be colder than Pluto. However, the planet is likely to maintain a massive atmosphere that would allow warmer temperatures at lower altitudes. It is even possible that interior heating by radioactive decays would be sufficient to make the surface as warm as the Earth, but theory suggests that the surface may be completely covered by a very deep ocean. This result also supports the 1996 prediction by Bennett and Sun Hong Rhie that the microlensing method should be sensitive to Earth-mass planets. "I'll hazard a prediction that the first extra-solar Earth-mass planet will be found by microlensing," Bennett said. "But we'll have to be very quick to beat the radial velocity programs and NASA's Kepler mission, which will be launched in early 2009." University of Notre Dame | |||||||||||||||||||||
|
Related Brown Dwarf News Articles Stellar still births The systematics of celestial bodies apparently needs to be revised. Researchers at the Argelander Institute of Astronomy of the University of Bonn have discovered that brown dwarfs need to be treated as a separate class in addition to stars and planets. Astronomers Weigh the Coldest Brown Dwarfs with Astronomy's Sharpest Eyes Astronomers have used ultrasharp images obtained with the Keck Telescope and Hubble Space Telescope to determine for the first time the masses of the coldest class of "failed stars," a.k.a. brown dwarfs. A Planet in Progress? Scientists are one step closer to understanding how new planets form, thanks to research funded by the National Science Foundation (NSF) and carried out by a team of astrophysicists at the American Museum of Natural History. Finally, the 'Planet' in Planetary Nebulae? Astronomers at the University of Rochester, home to one of the world's largest groups of planetary nebulae specialists, have announced that low-mass stars and possibly even super-Jupiter-sized planets may be responsible for creating some of the most breathtaking objects in the sky. XO-3b: Supersized planet or oasis in the 'brown dwarf desert'? The latest find from an international planet-hunting team of amateur and professional astronomers is one of the oddest extrasolar planets ever cataloged -- a mammoth orb more than 13 times the mass of Jupiter that orbits its star in less than four days. 28 new planets, 7 new brown dwarfs reported by California, Carnegie team The world's largest and most prolific team of planet hunters announced today (Monday, May 28) the discovery of 28 new planets outside our solar system, increasing to 236 the total number of known exoplanets. A Brown Dwarf Joins the Jet-Set Jets of matter have been discovered around a very low mass 'failed star', mimicking a process seen in young stars. This suggests that these 'brown dwarfs' form in a similar manner to normal stars but also that outflows are driven out by objects as massive as hundreds of millions of solar masses down to Jupiter-sized objects. Hubble finds 16 candidate extrasolar planets far across our Galaxy The NASA/ESA Hubble Space Telescope has discovered 16 extrasolar planet candidates that are orbiting a variety of distant stars. In accomplishing this, Hubble looked farther into our Milky Way galaxy than has ever successfully been done before in searching for extrasolar planets. Scientists snap images of first brown dwarf in planetary system Scientists using NASA's Spitzer Space Telescope have discovered and directly imaged a small brown dwarf star, 50 times the mass of Jupiter, orbiting with a planet around a Sun-like star. Planet or failed star? One of smallest stellar companions seen by Hubble Astronomers using the NASA/ESA Hubble Space Telescope have photographed one of the smallest objects ever seen around a normal star beyond our Sun. Weighing in at 12 times the mass of Jupiter, the object is small enough to be a planet. More Brown Dwarf News Articles |
|||||||||||||||||||||
|
|||||||||||||||||||||
|
|||||||||||||||||||||