Most Distant Object in Solar System Discovered
March 15, 2004
NASA-funded researchers have discovered the most distant object
orbiting Earth's Sun. The object is a mysterious planet-like body
three times farther from Earth than Pluto.
"The Sun appears so small from that distance that you could
completely block it out with the head of a pin," said Dr. Mike
Brown, California Institute of Technology, Pasadena, Calif.,
associate professor of planetary astronomy and leader of the
research team. The object, called "Sedna" for the Inuit goddess of
the ocean, is 13 billion kilometers (8 billion miles) away, in the
farthest reaches of the solar system.
This is likely the first detection of the long-hypothesized "Oort
cloud," a faraway repository of small icy bodies that supplies the
comets that streak by Earth. Other notable features of Sedna include
its size and reddish color. After Mars, it is the second reddest
object in the solar system. It is estimated Sedna is approximately
three-fourths the size of Pluto. Sedna is likely the largest object
found in the solar system since Pluto was discovered in 1930.
Brown, along with Drs. Chad Trujillo of the Gemini Observatory,
Hawaii, and David Rabinowitz of Yale University, New Haven, Conn.,
found the planet-like object, or planetoid, on Nov. 14, 2003. The
researchers used the 48-inch Samuel Oschin Telescope at Caltech's
Palomar Observatory near San Diego. Within days, telescopes in
Chile, Spain, Arizona and Hawaii observed the object. NASA's new
Spitzer Space Telescope also looked for it.
Sedna is extremely far from the Sun, in the coldest know region of
our solar system, where temperatures never rise above minus 240
degrees Celsius (minus 400 degrees Fahrenheit). The planetoid is
usually even colder, because it approaches the Sun only briefly
during its 10,500-year solar orbit. At its most distant, Sedna is
130 billion kilometers (84 billion miles) from the Sun, which is 900
times Earth's solar distance.
![size comparision of Sedna to Earth, Moon, Pluto and Quaoar](https://webarchive.library.unt.edu/eot2008/20080916075753im_/http://www.jpl.nasa.gov/images/sg_other/sedna-comp-300-240.jpg) |
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Size comparision of Sedna to Earth, Moon, Pluto and Quaoar.
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![](https://webarchive.library.unt.edu/eot2008/20080916075753im_/http://www.jpl.nasa.gov/images/spacer.gif) |
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Scientists used the fact that even the Spitzer telescope was unable
to detect the heat of the extremely distant, cold object to
determine it must be less than 1,700 kilometers (about 1,000 miles)
in diameter, which is smaller than Pluto. By combining available
data, Brown estimated Sedna's size at about halfway between Pluto
and Quaoar, the planetoid discovered by the same team in 2002.
The elliptical orbit of Sedna is unlike anything previously seen by
astronomers. However, it resembles that of objects predicted to lie
in the hypothetical Oort cloud. The cloud is thought to explain the
existence of certain comets. It is believed to surround the Sun and
extend outward halfway to the star closest to the Sun. But Sedna is
10 times closer than the predicted distance of the Oort cloud. Brown
said this "inner Oort cloud" may have been formed by gravity from a
rogue star near the Sun in the solar system's early days.
"The star would have been close enough to be brighter than the full
moon, and it would have been visible in the daytime sky for 20,000
years," Brown explained. Worse, it would have dislodged comets
farther out in the Oort cloud, leading to an intense comet shower
that could have wiped out some or all forms of life that existed on
Earth at the time.
Rabinowitz said there is indirect evidence that Sedna may have a
moon. The researchers hope to check this possibility with NASA's
Hubble Space Telescope. Trujillo has begun to examine the object's
surface with one of the world's largest optical/infrared telescopes,
the 8-meter (26-foot) Frederick C. Gillett Gemini Telescope on Mauna
Kea, Hawaii. "We still don't understand what is on the surface of
this body. It is nothing like what we would have predicted or what
we can explain," he said.
Sedna will become closer and brighter over the next 72 years, before
it begins its 10,500-year trip to the far reaches of the solar
system. "The last time Sedna was this close to the Sun, Earth was
just coming out of the last ice age. The next time it comes back,
the world might again be a completely different place," Brown said.
NASA's Jet Propulsion Laboratory, Pasadena, Calif, manages the
Spitzer Space Telescope. For more information about the research and
images on the Internet, visit
http://www.spitzer.caltech.edu/Media/releases/ssc2004-05. For
information about NASA on the Internet, visit http://www.nasa.gov.