[meteorite-list] Work Continues on the Solar System's Three Recently Discovered Kuiper Belt Objects

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri Sep 9 21:58:24 2005
Message-ID: <200509100157.j8A1vG808855_at_zagami.jpl.nasa.gov>

http://pr.caltech.edu/media/Press_Releases/PR12734.html
 
Work Continues on the Solar System's Three Recently Discovered Objects
Caltech News Release
September 8, 2005

CAMBRIDGE, England--When planetary scientists announced on July 29 that
they had discovered a new planet larger than Pluto, the news
overshadowed the two other objects the group had also found. But all
three objects are odd additions to the solar system, and as such could
revolutionize our understanding of how our part of the celestial
neighborhood evolved.

To the discoverers, the objects still go by the unofficial code-names
"Santa," "Easterbunny," and "Xena," though they are officially known to
the International Astronomical Union as 2003 EL61, 2005 FY9, and 2003
UB313. The three objects were all detected with the 48-inch Samuel
Oschin Telescope at Palomar Observatory by a team composed of planetary
scientists from the California Institute of Technology, the Gemini
Observatory, and Yale University. Xena is the object the group describes
as one of sufficient size to be called the tenth planet.

"All three objects are nearly Pluto-sized or larger, and all are in
elliptical orbits tilted out of the plane of the solar system," says
Mike Brown, a professor of planetary astronomy at Caltech and leader of
the effort.

"We think that these orbital characteristics may mean that they were all
formed closer to the sun, and then were tossed around by the giant
planets before they ended up with the odd orbits they currently have,"
Brown adds.

The other two members of the team are Chad Trujillo, a former
postdoctoral researcher at Caltech and currently an astronomer at the
Gemini Observatory in Hawaii, and David Rabinowitz of Yale University.
Trujillo has led the spectrographic studies of the discoveries, while
Rabinowitz is one of the builders of the instrument affixed to the
Oschin Telescope for the study, and has led the effort to understand the
color and spin of the objects.

Santa, Easterbunny, and Xena are all members of the Kuiper belt, a
region beyond the orbit of Neptune that for decades was merely a
hypothetical construct based on the behavior of comets, among other
factors. But astronomers began detecting objects in the mid-1990s, and
the Kuiper belt was suddenly a reality rather than a hypothesis.

Xena, which is currently about 97 astronomical units from the sun (an
astronomical unit being the 93-million-mile distance between the sun and
Earth), is at least the size of Pluto and almost certainly significantly
larger. The researchers are able to determine its smallest possible size
because, thanks to the laws of motion, they know very accurately the
distance of the planet from the sun. And because they also know very
precisely how much light the planet gives off, they can also calculate
the diameter of the planet as if it were reflecting sunlight as a
uniformly white ball in the sky. Hence, a perfectly round mirror at that
distance would be the size of Pluto.

However, the question remains how well the new planet reflects light.
The less reflective its surface, the bigger it must be to put out enough
light to be detected here on Earth.

At any rate, the researchers hope that infrared data returned by the
Spitzer Space Telescope over the weekend of August 27-28, in addition to
recently obtained data from the 30-meter IRAM telescope in Spain, will
help nail down Xena's size. In much the same way that the detected
visible light sets a lower limit on the diameter, the infrared radiation
detected by the Spitzer will ideally set an upper limit. That's because
the Spitzer is capable of measuring the total amount of heat given off
by the planet; and because the researchers know the likely surface
temperature is about 405 degrees below zero Fahrenheit, they can infer
the overall size of the body.

Brown predicts that Xena will likely be highly reflective, because the
spectrographic data gathered by his colleague and codiscoverer Chad
Trujillo at the Gemini Observatory show the surface to have a similar
composition to that of the highly reflective Pluto. If indeed Xena
reflects 70 percent of the sunlight reaching it, as does Pluto, then
Xena is about 2700 kilometers in diameter.

And then there's the matter of naming the new planet, which is pretty
much in the hands of the International Astronomical Union. Brown says
the matter is in "committee limbo": while one IAU committee is taking
its time deciding whether or not it is a planet, other committees have
to wait until they know what it is before they can consider a name. So
for the time being, the discoverers keep calling the new planet Xena,
though the name will sooner or later change.

The second of the objects, currently nicknamed Santa because Brown and
his colleagues found it on December 28, 2004, is one of the more bizarre
objects in the solar system, according to Rabinowitz. His observations
from a small telescope in Chile show that Santa is a fast-rotating
cigar-shaped body that is about the diameter of Pluto along its longer
axis. No large body in the solar system comes even close to rotating as
fast as Santa's four-hour period. Observations by Brown and his
colleagues at the Keck Observatory have shown that Santa also has a tiny
moon, nicknamed Rudolph, which circles it every 49 days. The third new
discovery is Easterbunny, so named because of its discovery earlier this
year on March 1. Easterbunny is also at 52 astronomical units, and like
Santa is probably about three-quarters the size of Pluto. Morever,
Easterbunny is now the third known object in the Kuiper belt, after
Pluto and Xena, which is known to have a surface covered in frozen
methane. For decades, Pluto was the only known methane-covered object
beyond Neptune, but "now we suddenly have three in a variety of sizes at
a variety of distances and can finally try to understand Pluto and its
cousins," says Kris Barkume, a PhD student working with Brown.

"With so many bright objects coming out at once it is hard to keep them
all straight," says Brown, adding that the remote region beyond Neptune
may present even more surprises in the future.

"We hope to discover a few more large objects in the outer solar system."

The research is funded by NASA. For more information see
http://www.gps.caltech.edu/~mbrown

Samuel Oschin Telescope: http://www.astro.caltech.edu/palomarnew/sot.html

Contact: Robert Tindol (626) 395-3631 tindol_at_caltech.edu
Received on Fri 09 Sep 2005 09:57:15 PM PDT