[meteorite-list] 2003 UB313 Is Larger than Pluto

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Feb 1 19:53:48 2006
Message-ID: <200602020052.k120q7x29775_at_zagami.jpl.nasa.gov>

Press and Public Relations Department
Max Planck Society for the Advancement of Science
Munich, Germany


Prof. Dr. Frank Bertoldi
Argelander-Institut f?r Astronomie der Universit?t Bonn, Bonn
Tel.: +49 228 73-6789

Dr. Wilhelm Altenhoff
Max Planck Institute for Radio Astronomy, Bonn
Tel.: +49 228 525-293

Prof. Dr. Karl M. Menten
Max Planck Institute for Radio Astronomy, Bonn
Tel.: +49 228 525-297

Dr. Norbert Junkes (MPIfR public outreach)
Max Planck Institute for Radio Astronomy, Bonn
Tel.: +49 2257 301-105

Embargoed: February 1st, 2006, 19:00

News / SP / 2006 (10)

New "Planet" Is Larger than Pluto

Bonn astronomers measure size of recently discovered solar system object

Claims that the Solar System has a tenth planet are bolstered by the
finding by a group lead by Bonn astrophysicists that this alleged planet,
announced last summer and tentatively named 2003 UB313, is bigger than
Pluto. By measuring its thermal emission, the scientists were able to
determine a diameter of about 3000 km, which makes it 700 km larger than
Pluto and thereby marks it as the largest solar system object found since
the discovery of Neptune in 1846 (Nature, 2 February 2006).

Like Pluto, 2003 UB313 is one of the icy bodies in the so-called Kuiper
belt that exists beyond Neptune. It is the most distant object ever seen
in the Solar System. Its very elongated orbit takes it up to 97 times
farther from the Sun than is the Earth -- almost twice as far as the most
distant point of Pluto's orbit -- so that it takes twice as long as Pluto
to orbit the Sun. When it was first seen, UB313 appeared to be at least as
big as Pluto. But an accurate estimate of its size was not possible
without knowing how reflective it is. A team lead by Prof. Frank Bertoldi
from the University of Bonn and the Max Planck Institute for Radio
Astronomy (MPIfR) and the MPIfR's Dr. Wilhelm Altenhoff has now resolved
this problem by using measurements of the amount of heat UB313 radiates to
determine its size, which when combined with the optical observations also
allowed them to determine its reflectivity. "Since UB313 is decidedly
larger than Pluto," Frank Bertoldi remarks, "it is now increasingly hard
to justify calling Pluto a planet if UB313 is not also given this status."

UB313 was discovered in January 2005 by Prof. Mike Brown and his
colleagues from the California Institute of Technology in a sky survey
using a wide field digital camera that searches for distant minor planets
at visible wavelengths. They discovered a slowly moving, spatially
unresolved source, the apparent speed of which allowed them to determine
its distance and orbital shape. However, they were not able to determine
the size of the object, although from its optical brightness it was
believed to be larger than Pluto.

Astronomers have found small planetary objects beyond the orbits of
Neptune and Pluto since 1992, confirming a then 40-year old prediction by
astronomers Kenneth Edgeworth (1880-1972) and Gerard P. Kuiper (1905-1973)
that a belt of smaller planetary objects beyond Neptune exists. The
so-called Kuiper Belt contains objects left from the formation of our
planetary system some 4.5 billion years ago. In their distant orbits they
were able to survive the gravitational clean-up of similar objects by the
large planets in the inner solar system. Some Kuiper Belt objects are
still occasionally deflected to then enter the inner solar system and may
appear as short period comets.

In optically visible light, the solar system objects are visible through
the light they reflect from the Sun. Thus, the apparent brightness depends
on their size as well as on the surface reflectivity. Latter is known to
vary between 4% for most comets to over 50% for Pluto, which makes any
accurate size determination from the optical light alone impossible.

The Bonn group therefore used the IRAM 30-meter telescope in Spain,
equipped with the sensitive Max-Planck Millimeter Bolometer (MAMBO)
detector developed and built at the MPIfR, to measure the heat radiation
of UB313 at a wavelength of 1.2 mm, where reflected sunlight is negligible
and the object brightness only depends on the surface temperature and the
object size. The temperature can be well estimated from the distance to
the sun, and thus the observed 1.2 mm brightness allows a good size
measurement. One can further conclude that the UB313 surface is such that
it reflects about 60% of the incident solar light, which is very similar
to the reflectivity of Pluto.

"The discovery of a solar system object larger than Pluto is very
exciting," Dr. Altenhoff exclaims, who has researched minor planets and
comets for decades. "It tells us that Pluto, which should properly also be
counted to the Kuiper Belt, is not such an unusual object. Maybe we can
find even other small planets out there, which could teach us more about
how the solar system formed and evolved. The Kuiper Belt objects are the
debris from its formation, an archeological site containing pristine
remnants of the solar nebula from which the sun and the planets formed."
Dr. Altenhoff made the pioneering discovery of heat radiation from Pluto
in 1988 with a predecessor of the current detector at the IRAM 30-meter

The size measurement of 2003 UB313 is published in the 2 February 2006
issue of Nature. The research team includes Prof. Dr. Frank Bertoldi (Bonn
University and MPIfR), Dr. Wilhelm Altenhoff (MPIfR), Dr. Axel Weiss
(MPIfR), Prof. Dr. Karl M. Menten (MPIfR), and Dr. Clemens Thum (IRAM).

The Kuiper Belt

UB313 is a members of a ring of some 100,000 objects on the outskirts of
the solar system, beyond Neptune at distances over 4 billion km from the
sun, over 30 times the distance between Earth and Sun. The objects in this
"Kuiper belt" circle the sun in stable orbits with periods of about 300
years. In the middle of the last century, the existence of a ring of small
planetary objects was first suggested by the astronomers Kenneth Edgeworth
(1880-1972) and Gerard P. Kuiper (1905-1973), but the first discovery of a
"Kuiper belt object" was not until 1992. By now, over 700 such objects are
known. UB313 is somewhat different from the normal Kuiper belt in that its
orbit is highly excentric and 45 degrees inclined to the ecliptic plane of
the planets and Kuiper Belt. It is likely that is originated in the Kuiper
Belt and was deflected to its inclined orbit by Neptune.For more detailed
information on the Kuiper belt, browse the web page by David Jewitt (see
link below).

Related Links:

* High-resolution images and additional information provided by the
* Information on 2003 UB313 by the discoverer Mike Brown
* David Jewitt's Kuiper Belt Page
* MAMBO detector
* IRAM 30-meter telescope

Original work:

F. Bertoldi, W. Altenhoff, A. Weiss, K.M. Menten, C. Thum
The trans-neptunian object UB313 is larger than Pluto
Nature, February 2, 2006


[Fig. 1:
The diameter of 2003 UB313 compared with that of the Pluto, Charon, Earth,
and the Moon.

Image: Max Planck Institute for Radio Astronomy

[Fig. 2:
http://www.astro.uni-bonn.de/~bertoldi/ub313/IRAM30m-2048.jpg (1.3MB)
http://www.astro.uni-bonn.de/~bertoldi/ub313/MAMBO-2-2048.jpg (1MB)]
To detect the very faint millimeter wavelength emission from UB313, the
Bonn group used the IRAM 30-m telescope on Pico Veleta in the south of
Spain, and the very sensitive heat sensor MAMBO-2, which was developed and
built at the MPIfR in Bonn by the group of Dr. Ernst Kreysa. The Institute
for Radio Astronomy at Millimeter wavelengths (IRAM) is supported jointly
by the German Max Planck Society, the French Centre National de Recherche
Scientifique (CNRS) and the Spanish Instituto Geogr?fico Nacional.

Image: Max Planck Institute for Radio Astronomy
Received on Wed 01 Feb 2006 07:52:06 PM PST

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