July 29, 2005
Caltech astronomer finds solar system’s 10th planet
By Gina Keating
LOS ANGELES (Reuters) - A California astronomer has
discovered what he believes is the 10th planet in our solar
system, a group of NASA-funded researchers said on Friday.
The new planet, known as 2003UB313, has been identified as
the most distant object ever detected orbiting the sun,
California Institute of Technology astronomer Michael Brown
Brown and colleagues Chad Trujillo and David Rabinowitz
have submitted a name for the planet to the International
Astronomical Union and are confident it will be designated a
planet. Brown did not reveal the proposed name.
The procedure for approving the new planet is somewhat hazy
as no new bodies have received that designation since Pluto was
discovered in 1930, Brown said.
"We hope that it's fairly noncontroversial among those who
believe Pluto is a planet," Brown said. "I would say get out
your pens and start rewriting the textbooks today."
The planet is located about 9.7 billion miles from the sun
and is about 1 1/2 times the size of Pluto, the researchers
The new planet orbits the sun once every 560 years and is
now at its farthest point from Earth, he said. In about 280
years, the planet will be as close as Neptune, he said.
Like Pluto, the object's surface is believed to be
predominantly methane, but its size -- about 1,700 miles in
diameter -- qualifies it as a planet, Brown said. Earth is
about 7,900 miles in diameter.
The new planet is believed to be part of the Kuiper Belt, a
large ring of icy objects that orbit beyond Neptune and are
believed to be remnants of the material that formed the solar
Brown said the new planet was detected in January by the
Samuel Oschin Telescope at the Palomar Observatory near San
The Caltech team, funded in part by NASA, had been waiting
to announce the find until they had completed their studies,
but changed their minds after a hacker threatened to go public
with their data, Brown said.
Their finding comes a day after a Spanish team of
astronomers announced the discovery of another relatively large
object orbiting in the solar system's outer reaches. That
object, Brown said, was about three-quarters the size of Pluto.
The new planet went undiscovered for so long because its
orbit is tilted at a 45-degree angle to the orbital plane of
the other planets, and travels in an elliptical orbit, Brown
The team had been scanning the skies with the 48-inch
(120-cm) telescope for five years, searching for large bodies
orbiting in higher planes than that of the Earth and other
The new planet is so far away that an observer standing on
its surface could cover the view of the sun with the head of a
pin, Brown said. It was sufficiently bright, however, for
amateur astronomers to track it in the early morning sky, he