And then there were ten?
http://physicsweb.org/articles/news/10/2/1/1

1 February 2006

Claims that our Solar System has a tenth planet have been supported by
new results from astronomers in Germany. Frank Bertoldi of the
University of Bonn and colleagues have found that "2003 UB313" -- an
icy object that was discovered last year lying beyond Nepture -- is
actually larger than Pluto itself. Although previous estimates
suggested that it was at least as big, Bertoldi's team have now
measured its size accurately and found that 2003 UB313 is 700 km larger
in diameter (Nature 439 563).

UB313 was discovered by Mike Brown and colleagues of the California
Institute of Technology in January 2005. It is one of a vast band of
small, icy bodies lying in the "Kuiper belt" beyond Neptune. Lying
almost twice as far from the Sun as the most distant point of Pluto's
orbit, it is the most distant known object in the solar system.

Astronomers initially suspected that UB313 was bigger than Pluto based
on measurements of the fraction of visible sunlight that it reflects
into space. The fraction is known as the "albedo" of the object. But
these measurements were tricky because UB313 is so far from Earth. They
also assumed that the body reflects light at optical wavelengths, like
Pluto does.

Bertoldi and colleagues have instead measured the thermal emission of
the object. Using a telescope operated by the Institute for Millimetre
Radio Astronomy in the Sierra Nevada mountains in southern Spain, they
measured the amount of heat radiated by UB313 at a wavelength of 1.2
mm, where the light reflected from the Sun is negligible.

The results, combined with optical measurements, reveal that UB313 is
about 3000 kilometres across. This is bigger than Pluto by 700 km and
also makes it the biggest solar system object to be found since Neptune
was discovered in 1846. "Since UB313 is decidedly larger than Pluto, it
is now increasingly hard to justify calling Pluto a planet if UB313 is
not also given this status," says Bertoldi.

"The discovery of a solar system object larger than Pluto is very
exciting," says team member Wilhelm Altenhoff of the Max Planck
Institute for Radio Astronomy, also in Bonn. "It tells us that Pluto,
which should properly also be counted to the Kuiper Belt, is not such
an unusual object."

The results also suggest that other "transneptunian planets" may be
lurking undiscovered in the far reaches of the Solar System. But
whether astronomers will accept UB313 as a planet is far from clear.

And then there were ten?
http://physicsweb.org/articles/news/10/2/1/1

1 February 2006

Claims that our Solar System has a tenth planet have been supported by
new results from astronomers in Germany. Frank Bertoldi of the
University of Bonn and colleagues have found that "2003 UB313" -- an
icy object that was discovered last year lying beyond Nepture -- is
actually larger than Pluto itself. Although previous estimates
suggested that it was at least as big, Bertoldi's team have now
measured its size accurately and found that 2003 UB313 is 700 km larger
in diameter (Nature 439 563).

UB313 was discovered by Mike Brown and colleagues of the California
Institute of Technology in January 2005. It is one of a vast band of
small, icy bodies lying in the "Kuiper belt" beyond Neptune. Lying
almost twice as far from the Sun as the most distant point of Pluto's
orbit, it is the most distant known object in the solar system.

Astronomers initially suspected that UB313 was bigger than Pluto based
on measurements of the fraction of visible sunlight that it reflects
into space. The fraction is known as the "albedo" of the object. But
these measurements were tricky because UB313 is so far from Earth. They
also assumed that the body reflects light at optical wavelengths, like
Pluto does.

Bertoldi and colleagues have instead measured the thermal emission of
the object. Using a telescope operated by the Institute for Millimetre
Radio Astronomy in the Sierra Nevada mountains in southern Spain, they
measured the amount of heat radiated by UB313 at a wavelength of 1.2
mm, where the light reflected from the Sun is negligible.

The results, combined with optical measurements, reveal that UB313 is
about 3000 kilometres across. This is bigger than Pluto by 700 km and
also makes it the biggest solar system object to be found since Neptune
was discovered in 1846. "Since UB313 is decidedly larger than Pluto, it
is now increasingly hard to justify calling Pluto a planet if UB313 is
not also given this status," says Bertoldi.

"The discovery of a solar system object larger than Pluto is very
exciting," says team member Wilhelm Altenhoff of the Max Planck
Institute for Radio Astronomy, also in Bonn. "It tells us that Pluto,
which should properly also be counted to the Kuiper Belt, is not such
an unusual object."

The results also suggest that other "transneptunian planets" may be
lurking undiscovered in the far reaches of the Solar System. But
whether astronomers will accept UB313 as a planet is far from clear.

And then there were ten?
http://physicsweb.org/articles/news/10/2/1/1

1 February 2006

Claims that our Solar System has a tenth planet have been supported by
new results from astronomers in Germany.