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- CHICAGO -- Scientists using a New Mexico telescope have discovered two
overgrown planets drifting alone in empty space -- the first such objects
ever found.
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- More massive than Jupiter but too small
to burn like our sun, the planetlike orbs represent a new type of extremely
faint space object that scientists say may be as common as the stars in
our galactic neighborhood.
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- Their discovery demonstrates the power
of the New Mexico-based Sloan Digital Sky Survey, said Johns Hopkins University
astronomer David Golimowski.
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- Golimowski and Princeton University astronomer
Xiaohui Fan announced the discovery of the new objects, called "methane
dwarfs," during this week's meeting of the American Astronomical Society.
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- Each is "too small to be a star
but probably too large to be called a planet," Fan said. But while
Jupiter and other similar objects have been found orbiting stars, Fan's
methane dwarf was all by itself in empty space.
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- Soon after Fan's discovery in early spring,
Golimowski found a second methane dwarf in data collected by the Sloan
telescope.
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- Follow-up observations with telescopes
in New Mexico and Hawaii showed methane in their atmospheres, as in the
atmosphere of Jupiter. The scientists have only a rough idea of the objects'
size but estimate they're 10 to 70 times the mass of Jupiter, the largest
planet in our solar system. That's at most 7 percent the size of our sun.
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- Located at Apache Point Observatory in
the mountains above Alamogordo, the Sloan is in the first year of a five-year
project to map the sky above the northern hemisphere in unprecedented detail.
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- It's a joint project of a consortium
of nine universities and research labs in the United States, Japan and
Germany. Fan discovered the first of the methane brown dwarfs by accident
while looking for the tell-tale signs of quasars -- giant objects in the
distant regions of the universe.
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- The faint red light from the methane
brown dwarfs drew his attention because it looked similar to the light
expected from a quasar. But when he began looking closely at the data,
he realized the object had important differences that meant it must be
a nearby object, tiny and faint. Scientists had expected objects like methane
dwarfs might exist in space -- indeed, one was discovered in 1995 orbiting
a star.
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- But no one knew whether methane dwarfs
could fly solo.
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- "We really didn't know whether these
things would exist free-floating in space," Golimowski said.
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- How they got there remains a mystery.
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- The scientists say they could have been
formed adjacent to a star and then flung out of orbit by a gravitational
slingshot. Or they could have formed by themselves in empty space from
a cloud of gas that collapsed under its own weight.
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- The light the telescope sees from the
object is a remnant of the heat created in its formation, like the fading
glow of a fireplace ember. The scientists don't know how far away the overgrown
planets are. But methane dwarfs give off very little light, and so the
fact that they can be seen at all indicates they must not be far away.
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- Golimowski estimated that they're within
30 light-years of Earth, an area in our neighborhood of the galaxy that
contains perhaps 300 of the stars nearest to us.
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- "They have to be quite near,"
Fan said.
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- And because two have been found in just
the small part of the sky already surveyed, it's likely that there are
many more to be found, with the number likely similar to the number of
stars in our neighborhood, Golimowski said.
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- Fan said the discoveries demonstrate
the power of the new kind of astronomy embodied in the Sloan.
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- Instead of pointing at a single object
an astronomer wants to study closely, the Sloan is slowly making its way
across the entire sky, sucking up data on millions of objects.
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- The scientists involved can then use
computers to study the attributes of large numbers of objects, looking
for oddballs like Fan's and Golimowski's methane dwarfs, and also a better
understanding of how the universe works. "We will be able to find
rare objects," Fan said. "As we cover more and more sky, we're
waiting for our mystery objects to show up."
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- "It gives us charts and plots and
graphs, things we can sink our teeth into and really tell what the universe
is like," said University of Chicago astronomer Constance Rockosi.
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