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Suspected protoplanet may really be a distant star
Posted: April 7, 2000

  Hubble image
This NASA Hubble Telescope near-infrared image of newborn binary stars reveals a long thin nebula pointing toward a faint companion object which was originally thought to be the first extrasolar planet to be imaged directly. Photo: S. Terebey (Extrasolar Research Corp.) and NASA
Follow-up observations of an unusual object initially suspected to be the first directly detected planet outside our solar system have shown that the object is too hot to be a planet.

Astronomers now believe it is more likely that the strange object is a background star whose light has been dimmed and reddened by interstellar dust, giving the illusion that it is in the vicinity of the double star system in which it was initially believed to have been a planet.

NASA's Hubble Space Telescope photographed the mysterious object, called TMR-1C, in 1997. The picture shows a bright dot at the end of a long streamer of reflective dust stretching 135 billion miles (225 billion kilometers) back to the binary star located 450 light-years away in the constellation Taurus the bull. A light year is about 6 trillion miles.

In 1998, astronomer Susan Terebey of the Extrasolar Research Corp., Pasadena, CA, reported her observation at a scientific meeting as a possible young and hot "protoplanet" several times the mass of Jupiter. Because of its potential importance and the compelling nature of the image, NASA also released the picture to the public with the caution that future observations would be critical in verifying whether or not this object actually is a planet.

Tereby initially proposed that the object had been ejected from a double star system via a "slingshot" effect (interaction with one of the stars or another giant planet). Since then she has conducted follow-up observations with the 10-meter Keck telescope in Mauna Kea, HI, to test her hypothesis.

Now, in results to be published in the May Astronomical Journal, Tereby reports, "The new data do not lend weight to the protoplanet interpretation and the results remain consistent with the explanation that TMR-1C may be a background star. Although the Hubble image is striking, there is the alternate possibility that TMR-1C is an unrelated background star, seen, by chance, projected close to the young star system. Finding a clearer answer is difficult for an object as faint as TMR-1C."

Identification of features in the original Hubble image from 1998. Photo: NASA
To better understand the nature of this faint object, Tereby used the Keck telescope to measure TMR-1C's temperature by dissecting its light through spectroscopy. Much like the way a prism disperses sunlight to make a colorful rainbow, a spectrum breaks apart the light from the observed object. The relative amounts of red and blue light help tell the object's temperature.

Tereby and colleagues then constructed models of dust-obscured objects to compare with the spectrum of TMR-1C and found a corresponding temperature of greater than 4400 degrees Fahrenheit (2700 degrees Kelvin) for TMR-1C. This is hotter than the predicted temperatures of young giant planets.

"However the models are not yet reliable at such young ages, so this test by itself is not conclusive," Tereby cautions. "The idea remains alive and well that there may be runaway planets and brown dwarfs (small stars that failed to sustain nuclear fusion) which formed via ejection from multiple star systems. Theoretical models by several groups support this idea, and new searches -- including ours -- are finding many new candidates in star-forming regions. However at this time there is no strong evidence that TMR-1C itself is a protoplanet."

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