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January 10, 2005 02:00 PM (EST)

News Release Number: STScI-2005-03

Hubble's Infrared Eyes Home in on Suspected Extrasolar Planet

An American Astronomical Society Meeting Release

January 10, 2005: The Hubble Space Telescope's near-infrared vision is hot on the trail of a possible planetary companion to a relatively bright young brown dwarf located 225 light-years away in the southern constellation Hydra. Astronomers at the European Southern Observatory's Very Large Telescope (VLT) in Chile detected the planet candidate in April 2004 with infrared observations. The astronomers spotted a faint companion object to the brown dwarf, called 2MASSWJ 1207334-393254 (2M1207). They suspect the companion is a planet because it is dimmer and cooler than the brown dwarf. Because a planet beyond our solar system has never been imaged directly, this remarkable observation required Hubble's unique abilities to perform follow-up observations to test and validate if the object is indeed a planet. Based on the VLT and Hubble observations, astronomers are 99 percent sure that the companion is orbiting the brown dwarf.

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Q & A: Understanding the Discovery

  1. 1. What are brown dwarfs?

  2. Brown dwarfs are gaseous objects with masses so low (15 to 80 times the mass of Jupiter, our solar system's largest planet) their cores cannot sustain thermonuclear fusion, the process that stars like the Sun need to shine steadily. These gaseous objects, therefore, dwell in limbo between low-mass stars and planets. They are too massive and hot to be classified as planets, but too small and cool to shine like stars. Depending on their size and age, brown dwarfs are about 10 to 1 million times fainter than Earth's Sun. As brown dwarfs get older, they fade and cool. The brown dwarf in the Hubble observation, dubbed 2M1207, is a youngster, about 8 million years old. The object is about 25 times more massive than Jupiter and a few hundred times fainter than our Sun. Scientists discovered the first brown dwarf in 1995. Once thought to be rare, scientists now believe that brown dwarfs are almost as abundant as stars.

  3. 2. Why do astronomers suspect that the companion object may be a planet and not a star or another brown dwarf?

  4. Astronomers think the companion is a planet because the object is much dimmer and cooler than the brown dwarf. They also think the companion, dubbed the Giant Planet Companion Candidate, has the mass of a planet. The suspected planet is about 5 times more massive than Jupiter. They deduced its mass by how it glows in infrared light. The candidate planet is 700 times fainter than the brown dwarf and glimmers at barely 1,800 degrees Fahrenheit, which is cooler than a light bulb filament. Astronomers know the object is not a star because stars are brighter, hotter, and more massive than brown dwarfs. Earth's Sun, for example, glows about 10 to 1 million times brighter than a brown dwarf.

  5. 3. How is the formation process different for stars, planets, and brown dwarfs?

  6. Stars form through the gravitational collapse of cold, dense clouds of gas. Planets grow through the buildup of tiny particles of stardust that make up a primeval disk of dust around a newborn star. Brown dwarfs, like full-fledged stars, would have fragmented and gravitationally collapsed out of a large cloud of hydrogen. They were not massive enough, however, to sustain fusion reactions at their cores.

  7. 4. Why have astronomers not been able to directly image planets outside our solar system, called extrasolar planets?

  8. Unlike stars, which generate light, planets reflect light. Planets, therefore, are so faint that they are lost in the glare of starlight from their parent stars. Although the suspected planet in the Hubble image is faint, it is very hot because it is young. Astronomers can see this heat in the glow of infrared light. In fact, the candidate planet appears much brighter in infrared light. That is why astronomers used infrared cameras, including Hubble's Near Infrared Camera and Multi-Object Spectrometer, to image the object. Hubble's infrared camera blocked out the light from the brown dwarf and imaged the infrared glow from the suspected planet.

  9. 5. How can astronomers detect whether the brown dwarf and suspected planet are gravitationally bound to each other?

  10. Through observations with the VLT and Hubble, astronomers look to see if the pair moves across the sky together. Astronomers are 99 percent certain that the two objects are on a gravitational leash. They are planning further Hubble observations to erase the 1 percent of doubt.

  11. 6. Have astronomers discovered extrasolar planets with the same mass as the suspected planet?

  12. Of the approximately 140 extrasolar planets detected so far, at least a few dozen are as massive as the suspected planet, which is five times more massive than Jupiter. None of the confirmed planets has been observed directly. They have been detected by measuring the gravitational pull a planet has on its parent star.

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Credit: NASA, ESA, G. Schneider (Steward Observ., Univ. of Arizona), I. Song (Gemini Observ.), B. Zuckerman, E. Becklin (Univ. of California, Los Angeles), P. Lowrance (California Inst. of Technology), B. Macintosh (Lawrence Livermore National Laboratory), M. Bessell (Australian National Univ.), and C. Dumas and G. Chauvin (European Southern Observ.)