RELEASE NO: 98-002

CLOSEST LOOK YET AT BETA PICTORIS SUPPORTS PLANETARY FORMATION THEORY

A team of astronomers using the newly installed Space Telescope Imaging Spectrograph (STIS) instrument on board the Hubble Space Telescope have achieved the most detailed close-up to date of a disk of gas and dust surrounding the young star Beta Pictoris. Analysis of the visible light images reveals new details regarding warps in the disk, supporting the theory that nascent planets may be forming inside and perturbing the disk through their gravitational influence. The team, led by Dr. Sally Heap of the Laboratory for Astronomy and Solar Physics at NASA’s Goddard Space Flight Center in Greenbelt, Md., will discuss its observations at a press conference beginning 9:30 a.m. EST Thursday, January 8 in Washington, D.C. during the winter meeting of the American Astronomical Society. The close-up view of the disk promises to shed light on the evolution of young stars and the nature of planet formation.

"These new images take us deeper into the Beta Pictoris solar system than ever before," said Heap. "The disk of matter around the star is more visibly warped than in any previous image, and the shape of the warp is a telltale indicator that favors the existence of a planet in this system."

Young stars like Beta Pictoris are thought to coalesce from a collapsing cloud of interstellar gas and dust. As the cloud falls inward, some of the material forms a flattened disk around the new star. It is thought that some of the material in the disk fragments and collapses further, forming planets in orbit around the star.

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"Observations of circumstellar disks are very difficult," said Heap. "It’s like trying to read street signs when the sun is in your eyes. Most of the light is coming directly from the star. Only a tiny fraction is reflected by material in the surrounding disk. The challenge is to separate the light from the star so we can see the disk. With Beta Pictoris, we need to get in close to the star, because that’s where the warps in the disk are. However, the closer we get to the star, the greater its glare is. We resolve this by using a coronagraph in the STIS instrument, which creates an artificial eclipse that blocks the light from the star so we can see the disk."

"Prior observations of Beta Pictoris were fantastic pieces of research that utilized instruments at the limits of their capabilities. However, the best image they could achieve begins at a distance from Beta Pictoris approximately equal to the distance between Pluto and the Sun, or 4 billion miles. This is not as close as the new STIS images, which take us in a little closer than Uranus, about 1.5 billion miles."

"Because we get in closer, we can start comparing the warps we observe to warps predicted by theories of their origin, and perhaps rule out some theories. For example, one proposal is that the warps are caused by pressure from the brilliant light of the star, rather than by the gravitational pull of a planet. However, the size and shape of a starlight induced warp is not like what we observe. The observed warp is compatible with a planet orbiting Beta Pictoris at a slight inclination to the disk. The planet’s gravity would tend to pull material toward itself as it progresses in its orbit, creating a symmetrical warp in the disk."

Observations of Beta Pictoris may afford us a glimpse into our own past. "Beta Pictoris is like a young Sun. If the Sun can be thought of as being fifty years old, Beta Pictoris is probably not a half year old yet. It’s nearly the same type of star, although slightly more massive, and it’s right in the neighborhood at a relatively close 60 light years. Its proximity lets us capture such detailed images. It’s a perfect place to explore because it may tell us something about our origins," said Heap.

"The observed size and shape of the warp doesn’t pin down where the planet is or how massive it might be. The planet could be quite close to the star and many times more massive than Jupiter or it may be far out from the star and only ten times the mass of the Earth. But that’s missing the point, anyway. The name of the game is to figure out what Beta Pictoris is trying to tell us. Either it will tell us how a planetary system forms, or we will learn that there are other avenues for stellar evolution. Planets are just one possibility," said Heap.

Note to Editors: Images to support this story may be found at:

http://www.gsfc.nasa.gov/ftp/newsmedia/JAN_AAS/DISK

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