Don Savage
Headquarters, Washington, DC                       February 9, 1999
(Phone:  202/358-1547)

Nancy Neal
Goddard Space Flight Center, Greenbelt, MD
(Phone:  301/286-0039)

Ray Villard
Space Telescope Science Institute, Baltimore, MD
(Phone:  410/338-4514)

RELEASE: 99-10

VAST STELLAR DISKS SET STAGE FOR
PLANET BIRTH IN NEW HUBBLE IMAGES

       Dramatic pictures of eerie disks of dust encircling young stars
are giving astronomers a new look at what may be the early formative
stages of planetary systems.

      Although these pictures from NASA's Hubble Space Telescope don't
show planets, the edge-on disks seen by Hubble provide some of the
clearest views to date of potential planetary construction zones, say
researchers.  The images also offer a peek at what happened 4.5
billion years ago when the Earth and other planets in our Solar System
began to condense out of a pancake-like disk of dust and gas centered
on the young Sun.

       Although more than a dozen possible extrasolar planets have
been discovered (though not imaged) over the past few years,
astronomers lack detailed pictures of environments around newborn
stars where planets form.    Even in nearby star-forming regions,
circumstellar disks are hard to see largely because the glare of the
central star overpowers the feeble reflected light from the disk.  An
exception occurs when the disk is close to edge-on, eclipsing the
infant sun.

       "While the existence of these disks has been known from prior
infrared and radio observations, the Hubble images reveal important
new details such as a disk's size, shape, thickness, and orientation,"
said Deborah Padgett of Caltech's Infrared Processing and Analysis
Center, Pasadena, CA.

       Padgett's group used Hubble's Near-Infrared Camera and Multi-
Object Spectrometer (NICMOS) to peer through obscuring dust clouds
surrounding six extremely young stars 450 light-years away in the
constellation Taurus.  Evidence for dusty disks was found in all six,
in the form of dark bands (dust lanes) crossing bright areas around
each star.  The presumed disks have sizes 8-16 times the diameter of
Neptune's orbit.

       "The NICMOS images show dark clumps and bright streamers above
and below the dust lanes, suggesting that raw material is still
falling into these disks and driving outflowing jets of gas from the
forming stars," Padgett said.  Padgett's results are reported in a
paper to appear in the March 1999 issue of The Astronomical Journal.

       Another group using Hubble has taken extremely sharp visible-
light pictures of disks in the same region.  John Krist of the Space
Telescope Science Institute, Baltimore, MD, found that the young star
Haro 6-5B is actually a small nebula crossed by a dust lane 10 times
the size of Neptune's orbit.

       Karl Stapelfeldt of NASA's Jet Propulsion Laboratory, Pasadena,
CA, used Hubble's Wide Field and Planetary Camera 2 to spot the first
example of an edge-on disk in a young double star system.  This disk
is centered on the system's faint companion star, and has a diameter
of only 3.5 times the diameter of Neptune's orbit.

       "The Hubble images of this disk offer further evidence that
planet formation should be possible in binary star systems," said
Stapelfeldt.  Theory suggests that gravitational forces in binary star
systems tend to tear apart fragile planet-forming disks.  Fitting
theoretical models to the color and reflectivity of the dust in the
disks observed, the team found evidence the dust grains were larger
than those found in interstellar space, suggesting that the dust is
clumping together and beginning to make larger bodies.

       Computer modeling of the Hubble images makes it possible to
estimate how much material is available in these disks to form
planets.  These estimates show the disks are about 1/200th to
1/10,000th the mass of the Sun (by comparison, the combined mass of
the planets in Earth's Solar System today is about 1/1,000th of the
Sun's mass).

       Only Hubble and the new generation of telescopes with adaptive
optics are able to see visible and near-infrared light evidence of
objects as small as our solar system around young stars in the nearest
stellar nurseries in the constellation Taurus.

       The Space Telescope Science Institute is operated by the
Association of Universities for Research in Astronomy, Inc. (AURA) for
NASA, under contract with NASA's Goddard Space Flight Center,
Greenbelt, MD.  The Hubble Space Telescope is a project of
international cooperation between NASA and the European Space Agency
(ESA).

- end -

EDITOR'S NOTE: Images and photo captions associated with this
release are available on the Internet at:
http://oposite.stsci.edu/pubinfo/pr/1999/05      or via links in:

http://oposite.stsci.edu/pubinfo/latest.html or
http://oposite.stsci.edu/pubinfo/pictures.html

Higher resolution digital versions (300 dpi JPEG) of the release
photos
are available at: http://oposite.stsci.edu/pubinfo/pr/1999/05.

TIFF image files are available at:
http://oposite.stsci.edu/pubinfo/tiff/1999/9905.tif.

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