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New evidence of significant atmosphere around the distant planet Pluto has been discovered, scientists at NASA's Jet Propulsion Laboratory, Pasadena, Calif., reported today in the British science journal Nature.

This latest discovery greatly enhances the stature of Pluto, which some astronomers have described as an asteroid masquerading as planet due to its small size, odd orbit and other characteristics more befitting an asteroid or other minor member of the solar system.

The new Pluto findings are based on results from the Infrared Astronomical Satellite (IRAS) and extensive observations through telescopes on Earth taken over the past three years.

JPL astronomers Edward F. Tedesco, Glenn J. Veeder and R. Scott Dunbar, and Larry A. Lebofsky of the University of Arizona reported that Pluto's overall temperature, as measured by IRAS twice in 1983, shows the planet to be very different from an asteroid or one of the icy moons of Jupiter or Saturn. The scientists said that Pluto's thermal characteristics support the suggestion that Pluto has significant atmosphere of methane.

Previous studies of Pluto found evidence of tenuous methane atmosphere. The new studies, however, indicate that Pluto's atmosphere may be much more extensive. (The atmosphere must contain other gases such as neon or argon, but these are not detectable from Earth.)

The results reported in Nature also refine the poorly known diameters of Pluto and its moon, Charon, to about 2,200 kilometers (1,370 miles) for Pluto and about 1,300 kilometers (800 miles) for Charon, each with an uncertainty of 150 kilometers or 100 miles. (For comparison, the Earth's Moon is about 2,475 kilometers (1,538 miles) in diameter.)

Very little is known about Pluto, which orbits the Sun every 248 years at an average distance of 6 billion kilometers (4 billion miles). The planet, which is the smallest in the solar system, was discovered by astronomer Clyde Tombaugh at the Lowell Observatory in 1930. Charon was discovered by James Christy of the U.S. Naval Observatory in 1978.

Pluto is the only solid-surfaced planet in the outer solar system; the rest -- Jupiter, Saturn, Uranus and Neptune, are giganitic gas planets.

A number of Pluto's characterisics have caused astronomers to question whether it deserves to be called planet. For example, Pluto has an elliptical and sharply tilted orbit -- one more suited to minor planet or asteroid. Its orbit is so skewed relative to the other planets that it actually crosses Neptune's orbital path; Pluto has been inside Neptune's orbit since 1980 and will remain there until 1999 when it again moves back to its ninth- place position from the Sun.

Pluto's relatively small size and theorized ice and rock composition makes it likely leftover from the formation of the solar system, or perhaps moon that escaped from Neptune's gravitational grasp. But the fact that Pluto has moon of its own, and now, apparently, substantial atmosphere, strongly bolsters its standing as planet.

The JPL scientists were supported in their research by NASA's Office of Space Science and Applications. JPL is operated for NASA by the California Institute of Technology.

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