[meteorite-list] 2003 UB313 Is Larger than Pluto

Ron Baalke baalke at zagami.jpl.nasa.gov
Wed Feb 1 19:52:06 EST 2006



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

Contact:

Prof. Dr. Frank Bertoldi
Argelander-Institut für Astronomie der Universität 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 
telescope.

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 
authors
  http://www.astro.uni-bonn.de/~bertoldi/ub313
* Information on 2003 UB313 by the discoverer Mike Brown
  http://www.gps.caltech.edu/~mbrown/planetlila/
* David Jewitt's Kuiper Belt Page
  http://www.ifa.hawaii.edu/faculty/jewitt/kb.html
* MAMBO detector
  http://www.mpifr-bonn.mpg.de/staff/bertoldi/mambo/
* IRAM 30-meter telescope
  http://www.iram.es/

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

IMAGE CAPTIONS:

[Fig. 1:
http://www.astro.uni-bonn.de/~bertoldi/ub313/EMPC-UB313-E-1200.gif 
(384KB)]
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 Geográfico Nacional.

Image: Max Planck Institute for Radio Astronomy






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