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Old 06-13-2002, 04:33 PM   #1
Drbio
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By Richard Stenger
CNN

(CNN) -- After spotting dozens of
planets in exotic orbits, scientists have
found a planetary system that looks
similar to our solar system.

The announcement came Thursday as
astronomers described the discovery of 15
new planets in other star systems,
including one that resembles Jupiter
around a sun-like star.

Known as 55 Cancri, the star system is
about 41 light years away and will likely
remain a place of particular interest as
astronomers begin to look for planets like
Earth in the coming years.

"This planetary system will be the best candidate for direct pictures when the
Terrestrial Planet Finder is launched later this decade," said planet hunter Debra
Fischer of the University of California, Berkeley, referring to one of NASA's next
generation of space telescopes.

The newly discovered jovian-like world takes about 13 years to revolve around its
parent star, compared with almost 12 years for Jupiter's journey around the sun.

The new planet has some significant differences. It
is roughly four times the mass of Jupiter and its
orbit is slightly elongated.

"We haven't found an exact solar system analog,
which would have a circular orbit and a mass closer
to that of Jupiter. But this shows we are getting
close," said Paul Butler of the Carnegie Institution, one of the leaders of the study,
funded by NASA and the National Science Foundation.

But the orbit of the Jupiter-like planet is stable enough to foster a benign,
life-friendly environment in the inner solar orbit, the astronomers said.

Jupiter, the largest planet in our solar system, is thought to have protected
terrestrial life in its infancy, ingesting dangerous hordes of comets before they
collided with our planet.

Dozens of so-called exoplanets have been detected in recent decades. They tend to
travel in highly elliptical and contorted orbits, usually much closer and faster than
large planets in our solar system.

For example, a planet slightly less massive than Jupiter, discovered earlier by the
same scientific team, orbits 55 Cancri every two weeks from a distance closer than
Mercury to the sun.

Theoretical models suggest that a small rocky world like Earth could survive in an
orbit between the two planets.

But whether a terrestrial planet lurks near
the star will remain a matter of speculation
for some time. The hunt for exoplanets has
turned up only gas giants so far because of
the limits of current search methods.

By observing the gravitational tug on stars
over time, astronomers deduce the
existence of exoplanets as well as estimate
their mass, orbital paths and revolution
periods.

Ground-based observatories and space
telescopes like the Terrestrial Planet Finder might allow scientists to directly detect
planets, including small ones like our own.

In the meantime, refinement of the star-wobble technique should keep astronomers
plenty busy. Fischer, Butler and colleagues, the most experienced team of planet
hunters, are finding increasingly smaller planets in their ongoing survey of more
than 1,200 stars.

The new discoveries, announced at NASA headquarters in Washington, D.C.,
include another planet around 55 Cancri, a star visible to the naked eye in the
constellation Cancer; and the smallest known exoplanet, one near the star HD49674
with less than half the mass of Saturn.
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