July 29, 2005
Astronomers have found a new planet in
the outer reaches of the solar system
July 29, 2005: "It's definitely
bigger than Pluto." So says Dr. Mike Brown of the California Institute
of Technology who announced today the discovery of a new planet in the
outer solar system.
The planet, which hasn't been officially named yet, was found by Brown
and colleagues using the Samuel Oschin Telescope at Palomar Observatory
near San Diego. It is currently about 97 times farther from the sun
than Earth, or 97 Astronomical Units (AU). For
comparison, Pluto is 40 AU from the sun.
This places the new planet more or less in the Kuiper
Belt, a dark realm beyond Neptune where thousands of small icy
bodies orbit the sun. The planet appears to be typical of Kuiper Belt
objects--only much bigger. Its sheer size in relation to the nine known
planets means that it can only be classified as a planet itself, Brown
Backyard astronomers with large telescopes can see the new planet. But
don't expect to be impressed: It looks like a dim speck of light,
visual magnitude 19, moving very slowly against the starry background.
"It is currently almost directly overhead in the early-morning eastern
sky in the constellation Cetus," notes Brown.
The planet was discovered by, in addition to Brown, Chad Trujillo, of
the Gemini Observatory in Mauna Kea, Hawaii, and David Rabinowitz, of
Yale University, New Haven, Connecticut. They first photographed the
new planet with the 48-inch Samuel Oschin Telescope on October 31,
2003. The object was so far away, however, that its motion was not
detected until they reanalyzed the data in January of this year. In the
last seven months, the scientists have been studying the planet to
better estimate its size and its motions.
"We are 100 percent confident that this is the first object bigger than
Pluto ever found in the outer solar system," Brown adds.
The new planet, circled in white, moves across a field of stars on Oct.
21, 2003. The three photos were taken about 90 minutes apart. Image
credit: Samuel Oschin Telescope, Palomar Observatory. Images
Telescopes have not yet revealed the planet's disk. To estimate how big
it is, the astronomers must rely on measurements of the planet's
brightness. Like all planets, this new one presumably shines by
reflecting sunlight. The bigger the planet, generally speaking, the
bigger the reflection. The reflectance, the fraction of light that
bounces off the planet, is not yet known. Nevertheless, it is possible
to set limits on the planet's diameter:
"Even if it reflected 100 percent of the light reaching it, it would
still be as big as Pluto," says Brown. Pluto is 1400 miles (2300 km)
wide. "I'd say it's probably [about] one and a half times the size of
Pluto, but we're not sure."
The planet's temporary name is 2003 UB313. A permanent name has been
proposed by the discoverers to the International Astronomical Union,
and they are awaiting the decision of this body before announcing the
name. Stay tuned!
Article (No longer available in 2021)
UPDATE (September 23th, 2021):
On September 13, 2006, following an unusually long period in which the
object was known by the provisional designation 2003 UB313, it was
named Eris, after the Greek goddess Eris, a
personification of strife and discord. The planet was
discovered in January 2005 and announced in July 2005. (Source)
It was in
April of the same year when the Vatican administrators named Joseph Ratzinger "Pope".
The M+G+R Foundation
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