Donald Savage
Headquarters,Washington April 17, 2002
(Phone: 202/358-1727)
Ray Villard
Space Telescope Science Institute, Baltimore
(Phone: 410/338-4514)
Nancy Neal
Goddard Space Flight Center, Greenbelt, Md.
(Phone: 301/286-0039)
Christian Veillet
Canada-France-Hawaii Telescope Corporation, Kamuela, Hawaii
(Phone: 808/885-3161)
RELEASE: 02-70
HUBBLE HUNTS DOWN ODD COUPLES AT THE FRINGES OF OUR SOLAR
SYSTEM
NASA's Hubble Space Telescope is hot on the trail of an
intriguing new class of solar system object that might be
called a Pluto "mini-me" -- dim and fleeting objects that
travel in pairs in the frigid, mysterious outer realm of the
solar system called the Kuiper Belt.
In results published today in the journal Nature, a team of
astronomers led by Christian Veillet of the Canada-France-
Hawaii Telescope Corporation (CFHT) in Kamuela, Hawaii, is
reporting the most detailed observations yet of the Kuiper
Belt object (KBO) 1998 WW31, which was discovered four years
ago and found to be a binary last year by the CFHT.
Pluto and its moon Charon and countless icy bodies known as
KBOs inhabit a vast region of space called the Kuiper Belt.
This "junkyard" of material left over from the solar system's
formation extends from the orbit of Neptune out to 100 times
as far as the Earth is from the Sun (which is about 93
million miles) and is the source of at least half the short-
period comets that whiz through our solar system. Only
recently have astronomers found that a small percentage of
KBOs are actually two objects orbiting around each other,
called binaries.
"More than one percent of the approximately 500 known KBOs
are indeed binary: a puzzling fact for which many
explanations will be proposed in what is going to be a very
exciting and rapidly evolving field of research in the coming
years," says Veillet.
Hubble was able to measure the total mass of the pair based
on their mutual 570-day orbit (a technique Isaac Newton used
400 years ago to estimate the mass of our Moon). Together,
the "odd-couple" 1998 WW31 is about 5,000 times less massive
than Pluto and Charon.
Like a pair of waltzing skaters, the binary KBOs pivot around
a common center of gravity. The orbit of 1998 WW31 is the
most eccentric ever measured for any binary solar-system
object or planetary satellite. Its orbital distance varies by
a factor of ten, from 2,500 to 25,000 miles (4,000 to 40,000
kilometers). It is difficult to determine how KBOs wind up
traveling in pairs. They may have formed that way, born like
twins, or may be produced by collisions where a single body
is split in two.
Ever since the first KBO was discovered in 1992, astronomers
have wondered how many KBOs may be binaries, but it was
generally assumed that the observations would be too
difficult for most telescopes. However, the insights to be
gained from study of binary KBOs would be significant:
measuring binary orbits provides estimates of KBO masses, and
mutual eclipses of the binary allow astronomers to determine
individual sizes and densities. Assuming some fraction of
KBOs should be binary -- just as has been discovered in the
asteroid belt -- astronomers eventually began to search for
gravitationally entwined pairs of KBOs.
Then, finally, exactly a year ago on April 16, 2001, Veillet
and collaborators announced the first discovery of a binary
KBO: 1998 WW31. Since then, astronomers have reported the
discoveries of six more binary KBOs. "It's amazing that
something that seems so hard to do and takes many years to
accomplish can then trigger an avalanche of discoveries,"
says Veillet. Four of those discoveries were made with the
Hubble Space Telescope: two were discovered with a program
led by Michael Brown of the California Institute of
Technology in Pasadena, Calif., and two more with a program
led by Keith Noll of the Space Telescope Science Institute in
Baltimore. The sensitivity and resolution of Hubble is ideal
for studying binary KBOs because the objects are so faint and
so close together.
The Kuiper Belt is one of the last big missing puzzle pieces
to understanding the origin and evolution of our solar system
and planetary systems around other stars. Dust disks seen
around other stars could be replenished by collisions among
Kuiper Belt-type objects, which seems to be common among
stars. These collisions offer fundamental clues to the birth
of planetary systems.
-end-
Electronic image files, animation, illustrations and
additional information are available on the Internet at:
http://oposite.stsci.edu/pubinfo/pr/2002/04
http://oposite.stsci.edu/pubinfo/latest.html
http://oposite.stsci.edu/pubinfo/pictures.html
http://hubblesite.org/go/news
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