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New Tools, New Discoveries
Much of astronomy
involves the search for the barely visiblea category that
describes the overwhelming majority of objects in the universe,
at least for the time being. One of today's most effective tools
for detecting what cannot be seen is Arecibo Observatory in Puerto
Rico, the site one of the world's largest and most powerful telescopes
for radar and radio astronomy. Operated by Cornell University under
a cooperative agreement with NSF, the Arecibo telescope collects
extraterrestrial radio waves of almost imperceptible intensity in
a 1,000-foot-wide dish. This telescope, used by scientists from
around the world, is a dual-purpose instrument. About three-quarters
of the time, the telescope detects, receives, amplifies, and records
signals produced by distant astronomical objects. The rest of the
time, it measures reflected radio signals that were transmitted
by its antenna. The signals bounce off objects such as planets,
comets, and asteroids, allowing researchers to determine each object's
size and motion.
It
was at Arecibo in 1991 that Alexander Wolszczan of Pennsylvania
State University discovered the first three planets found outside
our solar system. With support from NSF, Wolszczan discovered these
planets by timing the radio signals coming from a distant pulsara
rapidly rotating neutron star7,000 trillion miles from Earth
in the constellation Virgo. He saw small, regular variations in
the pulsar's radio signal and interpreted them as a complicated
wobble in the pulsar's motion induced by planets orbiting the pulsar.
Two of the planets are similar in mass to the Earth, while the mass
of the third is about equal to that of our moon. It is unlikely
that any of these newly discovered planets support life, because
the tiny pulsar around which they orbit constantly bombards them
with deadly electromagnetic radiation. Wolszczan's work helps astronomers
understand how planets are formed, and his discovery of planets
around an object as exotic as a pulsar suggests that planets may
be far more common than astronomers had previously thought.
In 1995, four years after Wolszczan's discovery, two Swiss astronomers
announced that they had found a fourth new planet, orbiting a star
similar to the Sun. Two American astronomers, Geoffrey Marcy and
Paul Butler, confirmed the discovery and, the following year, announced
that their NSF-supported work culminated in the discovery of another
two planets orbiting sun-like stars. Using an array of advanced
technologies and sophisticated analytic techniques, Marcy, Butler,
and other astronomers have since discovered four more extrasolar
planets. An especially astonishing discovery was made in 1999 by
two independent NSF-supported teams of the first multi-planet system-other
than our own-orbiting its own star. At least three planets were
found by Marcy, Butler, and others to be circling the star Upsilon
Andromedae, making it the first solar system ever seen to mimic
our own.
By August 2000,
the number of extrasolar planets had topped 50, and more such sightings
were expected. Based on the discovery of these planets, it seems
as if the Milky Way is rife with stars supporting planetary systems.
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