[meteorite-list] Moon Discovered Orbiting 10th Planet (2003 UB313)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Oct 4 12:25:28 2005
Message-ID: <200510041624.j94GOD920011_at_zagami.jpl.nasa.gov>

W.M. Keck Observatory
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Kamuela, HI 96743

Media Contact:
Laura K. Kraft, (808) 885-7887

October 3, 2005

MOON DISCOVERED ORBITING 10th PLANET

New Class of Satellites Discovered

MAUNA KEA, Hawaii -- Scientists are over the moon at the W. M. Keck
Observatory and the California Institute of Technology over a new
discovery of a satellite orbiting the Solar System's 10th planet (2003
UB313). The newly discovered moon orbits the farthest object ever seen in
the Solar System. The existence of the moon will help astronomers resolve
the question of whether 2003 UB313, temporarily nicknamed "Xena," is more
massive than Pluto and hence the 10th planet. A paper describing the
discovery was submitted to the Astrophysical Journal Letters on October 3,
2005.

"We were surprised because this is a completely different type of
satellite from anything we've seen before," said Dr. Mike Brown, professor
of Planetary Sciences at the California Institute of Technology in
Pasadena. "It is essentially a new class of satellites to large Kuiper
Belt objects. It is tiny compared to the primary, and much fainter. We
have never seen satellites like this before."

The newly discovered moon, which is 60 times fainter than its parent body,
is affectionately called "Gabrielle" after the faithful traveling
companion to Xena on the syndicated TV series. Future observations with
the 10-meter Keck II telescope and the Hubble Space Telescope will
determine the moon's orbital characteristics, which has an estimated
period of about 14 days, and will therefore reveal the precise mass and
density of Xena.

"What is interesting is that Xena, Pluto and Santa, three of the four
largest objects in the Kuiper belt, all have moons," said Dr. Marcos van
Dam, adaptive optics scientist at the W. M. Keck Observatory and co-author
on the paper describing the discovery. "These moons suggest that these
Kuiper belt objects may have formed differently than smaller objects in
the same region."

The moon circling Xena was first discovered with the Keck II telescope on
September 10, 2005 (UT) using the Laser Guide Star Adaptive Optics system
(LGS AO). Since 2003, this system has been providing very high spatial
resolution imaging in the infrared comparable to that of visible light
images from Hubble Space Telescope. With LGS AO, observers not only get
higher resolution, but the light from distant objects is concentrated over
a much smaller area on the instrument detector, making faint detections
possible. The results are quickly advancing the understanding of binary
Kuiper belt objects, a region in the Solar System beyond the orbit of
Neptune.

The Keck LGS AO system has also been used to look at other recently
discovered large bodies in the Kuiper belt. A small moon was found
circling around 2003 EL61 (codenamed "Santa") but none was found orbiting
2005 FY9 ("Easterbunny"), the two largest known Kuiper belt objects after
Xena and Pluto.

"When we test collision models to predict how Pluto and Charon formed, the
models kept producing tiny satellites, much smaller than Charon," added
Brown "But we had never seen satellites that small before in the Kuiper
belt. But then we found a moon in the Santa system, and then we found
another moon circling Xena, and they both look very similar to one
another. This leads us to conclude that the largest objects in the Kuiper
belt may have been subject to collisions."

Van Dam described the discovery: "At first we saw this little faint thing
that kept cropping up in all the images, and we knew it was not a
background star or galaxy because it moved across the sky with the
primary. We could also tell that it was not an image artifact because it
did not rotate with the sky and was consistent in each of the 24 images.
By morning we knew that we had made a major discovery."

The discovery of the moon's primary, Xena, was announced July 29th by
planetary astronomers Mike Brown of Caltech, Chad Trujillo of Gemini
Observatory and David Rabinowitz of Yale University. It is currently about
97 astronomical units from the Sun (an astronomical unit is the
93-million-mile distance between the Sun and Earth), and is larger than
the size of Pluto. It takes 560 years to complete one trip around the Sun
(versus 250 years for Pluto) and has a very steep angle in relation to the
other planets, about 45 degrees off from the orbital plane of the other
nine planets. Xena also has a very elliptical orbit, coming in as close as
3.5 billion miles (38 AU) and as far away as 9 billion miles.

The names "Xena," "Gabrielle," "Santa" and "Easterbunny" are temporary
nicknames until the International Astronomical Union (IAU) rules on their
official names. The proposed names have been submitted to the IAU and will
follow the mythological and spiritual traditions of Kuiper belt objects.
Meanwhile, the IAU has stated it will not rule on a name until the IAU
Working Group in charge of defining a planet determines a minimum size for
a planet. Until then, the IAU considers all objects discovered in the
outer solar system as "Trans-Neptunian" objects.

Adaptive Optics is a technique that corrects the effect of atmospheric
blurring to produce images with a resolution comparable to what would be
obtained from space. To measure atmospheric distortion, the adaptive
optics system relies on a relatively bright guide star very close in the
field of view to the scientific object of study. Since there was no
naturally-occurring guide star sufficiently bright enough with which to
study Xena, astronomers used the Keck Laser Guide Star system to create an
artificial star instead.

The team responsible for the discovery of Gabrielle, a moon orbiting 2003
UB313, are Michael E. Brown and Antonin H. Bouchez of California Institute
of Technology in Pasadena; Marcos A. van Dam, David Le Mignant, Randall D.
Campbell, Jason C. Y. Chin, Al Conrad, Scott K. Harman, Erik M. Johansson,
Robert E. Lafon, Paul J. Stomski Jr., Douglas M. Summers and Peter L.
Wizinowich of the W. M. Keck Observatory in Hawaii; Chadwick A. Trujillo
of Gemini Observatory in Hawaii and David L. Rabinowitz of Yale University
in Connecticut.

The W. M. Keck Observatory at Mauna Kea is home to twin 10-meter
telescopes, the world's largest. The facility is managed by the California
Association for Research in Astronomy, a non-profit 501 (c) (3)
partnership established by California Institute of Technology and the
University of California. In 1996, NASA joined as a partner. For more
information please visit www.keckobservatory.org .

Additional Information:

* ApJ Letters Paper
  http://www2.keck.hawaii.edu/news/science/051003_gabrielle/gab.pdf
* Discovery of Gabrielle
  http://www2.keck.hawaii.edu/optics/staff/mvandam/gabrielle.html

IMAGE CAPTION:
[http://www2.keck.hawaii.edu/news/science/051003_gabrielle/Xena_print.jpg
(385KB)]
An image of the most distant planet (2003 UB313) ever found in the Solar
System. A companion (right) was discovered at Keck Observatory on
September 10, 2005 (UT).

This near-infrared image is a composite of 24 exposures taken at 2.1
micron wavelength with the Laser Guide Star Adaptive Optics System on the
Keck II telescope on Mauna Kea. The ability of the system to detect
extremely faint objects at high spatial resolution is advancing the
understanding of binary Kuiper belt objects.

Credit: W. M. Keck Observatory
Received on Tue 04 Oct 2005 12:24:12 PM PDT