NASA Notes New Planetoid

NASA Notes New Planetoid
Named Sedna

Scientists on Monday announced the discovery of a frozen, shiny
red world some 8 billion miles from Earth that is the most distant
known object in the solar system.

They are calling it a "planetoid," saying it does not
meet the definition of a planet.

"There's absolutely nothing like it known in the solar system," said
Mike Brown, the California Institute of Technology astronomer who
led the NASA-funded team that found it last year.

Named Sedna, after the Inuit goddess who created the sea creatures
of the Arctic, the planetoid is 800 to 1,100 miles in diameter,
or about three-quarters the size of Pluto, and probably half rock,
half ice.

It is currently three times farther from Earth than Pluto, the
ninth and outermost planet.

Sedna is the largest object found orbiting the sun since the discovery
of Pluto in 1930. It trumps in size another icy world, called Quaoar,
discovered by the same team in 2002.

Sedna follows a highly elliptical path around the sun, a circuit
that takes 10,500 years to complete. It loops out as far as 84
billion miles from the sun. From Sedna's surface, the sun would
appear so small that it could be blocked out by the head of a pin.

It is well beyond the Kuiper Belt, a region of ice and rock just
beyond the orbit of Neptune.

Brown and his colleagues believe Sedna is the first known member
of the long-hypothesized Oort Cloud, a sphere of material orbiting
the sun that explains certain comets. If Sedna is part of the Oort
Cloud, the cloud extends much closer inward toward the sun than
previously believed.

The Oort theory holds that comets in the cloud probably started
out as icy objects in places like the Kuiper Belt that were flung
out of the solar system by one of the giant planets.

The location of Sedna suggests that it got stuck where it is because
its orbit was affected long ago by a star that is no longer nearby.

"What we think must have happened is that early in the history
of the solar system, there must have been many, more stars very
close to the sun than there are now," Brown said. The sun,
in other words, was born in a tight cluster of many stars.

Sedna is one of the most pristine objects in the solar system.

"Very little has happened to this object since the beginning
of the solar system," Brown said. "There's not much else
out there, so it hasn't been impacted by other objects, it hasn't
been heated by the sun. It really has just been sitting out there
at 400 degrees below zero for the past 4.5 billion years."

Brown would not classify Sedna as a planet, based on a definition
of a planet as an object considerably more massive than any other
object in a similar location.

"Sedna sits all by itself in the very outer reaches of the
solar system, but our prediction is there will be many, many more
of these objects found over the next five years or over the next
decade, and it will turn out that Sedna, in fact, is not the most
massive object in its orbit out there," Brown said.

Brown, Chad Trujillo of the Gemini Observatory in Hawaii, and
David Rabinowitz of Yale University discovered Sedna last November,
using a 48-inch telescope at Caltech's Palomar Observatory east
of San Diego.

Within days, other astronomers around the world trained their
telescopes, including the recently launched Spitzer Space Telescope,
on the object.

"It took us a few weeks of continuing to see this object
until we were really convinced we had stumbled on something big," Brown
said.

The team also have indirect evidence a tiny moon may trail Sedna,
which is redder than all other known solar system bodies except
Mars.