Planetary scientists at the California Institute of
Technology and Yale University on Tuesday night discovered a new
planetoid in the outer fringes of the solar system.

The planetoid, currently known only as 2004 DW, could be even larger
than Quaoar–the current record holder in the area known as the
Kuiper Belt–and is some 4.4 billion miles from Earth.

According to the discoverers, Caltech associate professor of
planetary astronomy Mike Brown and his colleagues Chad Trujillo (now
at the Gemini North observatory in Hawaii), and David Rabinowitz of
Yale University, the planetoid was found as part of the same search
program that discovered Quaoar in late 2002. The astronomers use the
48-inch Samuel Oschin Telescope at Palomar Observatory and the
recently installed QUEST CCD camera built by a consortium including
Yale and the University of Indiana, to systematically study different
regions of the sky each night.

Unlike Quaoar, the new planetoid hasn’t yet been pinpointed on old
photographic plates or other images. Because its orbit is therefore
not well understood yet, it cannot be given an official name.

“So far we only have a one-day orbit,” said Brown, explaining that
the data covers only a tiny fraction of the orbit the object follows
in its more than 300-year trip around the sun. “From that we know
only how far away it is and how its orbit is tilted relative to the
planets.”

The tilt that Brown has measured is an astonishingly large 20
degrees, larger even than that of Pluto, which has an orbital
inclination of 17 degrees and is an anomaly among the otherwise
planar planets.

The size of 2004 DW is not yet certain; Brown estimates a size of
about 1,400 kilometers, based on a comparison of the planetoid’s
luminosity with that of Quaoar. Because the distance of the object
can already be calculated, its luminosity should be a good indicator
of its size relative to Quaoar, provided the two objects have the
same albedo, or reflectivity.

Quaoar is known to have an albedo of about 10 percent, which is
slightly higher than the reflectivity of our own moon. Thus, if the
new object is similar, the 1,400-kilometer estimate should hold. If
its albedo is lower, then it could actually be somewhat larger; or if
higher, smaller.

According to Brown, scientists know little about the albedos of
objects this large this far away, so the true size is quite
uncertain. Researchers could best make size measurements with the
Hubble Space Telescope or the newer Spitzer Space Telescope.

The continued discovery of massive planetoids on the outer fringe of
the solar system is further evidence that objects even farther and
even larger are lurking out there. “It’s now only a matter of time
before something is going to be discovered out there that will change
our entire view of the outer solar system,” Brown says.

The team is working hard to uncover new information about the
planetoid, which they will release as it becomes available, Brown
adds. Other telescopes will also be used to better characterize the
planetoid’s features.