Glimpses of alien comets and planets?

Glimpses of alien comets and planets?

Looking for evidence of planetarysystems other than our own, astronomers search nebulas that surround various strs for evidence that the material follows Keplerian orbits. Solid material -- comets, planets, etc. -- should move according to Kepler's laws; the gas is more common in circumstellar nebulas generally does not. In Pasadena, Calif., at the recent meeting of the American Astronomical Society, scientists reported three such nebulas in the form of disks around the stars Beta Pictoris, HL Tauri and T Tauri.

Two groups presented new images ofthe Beta Pictoris disk. Francesco Paresce and Christopher Burrows of the Space Telescope Science Institute in Baltimore and the European Space Agency claim that their image is the first picture of the Beta Pictoris disk in visible light. Benjamin Zuckerman of the University of California at Los Angeles, whose group worked at a wavelength of 9,000 angstroms, on the edge of visible light (between infrared and red), held a similar claim.

Whoever was first, both groups findevidence for cometary material in the disk. Paresce refers to "pebble-sized particles," 10 times as large as anything found in interstellar space. Zuckerman speaks of a giant Oort cloud surrounding Beta Pictoris. Our solar system's Oort cloud consists of cometary material orbiting the sun far beyond the outermost planets. Occasionally an object separates from it and enters the inner solar system as a comet. Zuckerman, whose group includes Harland W. Epps of UCLA, Colin R. Masson of Caltech in Pasadena, Jonathan C. Gradie and Joan N. Hayashi of the University of Hawaii in Manoa and Robert Howell of the University of Wyoming in Laramie, calculates the mass of the cometary material encircling Beta Pictoris as equal to that of Jupiter.

In addition, David Weintraub ofUCLA, Zuckerman, Masson and James Benson of the University of Wyoming did the observations of T Tauri, a binary star system, in which two stars orbit each other. This group finds material equal to a few times the mass of Jupiter orbiting the whole binary system.

Anneila I. Sargent of Caltech andSteven Beckwith of Cornell University did the observations of HL Tauri. They find Keplerian motion in a disk extending to 500 astronomical units (500 times the earth's distance from the sun, or about 50 billion miles) out from the star. This could contain gas plus comets with dust nearby. Sargent suggests that this is how a solar system might look before planets begin to coalesce.