[meteorite-list] Beyond Pluto: Max-Planck Radioastronomers Measure The Sizes Of Distant Minor Planets

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:06:57 2004
Message-ID: <200210082219.PAA09132_at_zagami.jpl.nasa.gov>

http://www.mpifr-bonn.mpg.de/staff/bertoldi/kbo/pr_kbo_e.html

Max-Planck-Institut für Radioastronomie
Bonn, Germany

Contact:

Dr. Frank Bertoldi
Tel.: +49 - 228 - 525-377 or +49 - 179 - 8567872
Fax: +49 - 228 - 525-229
e-mail: bertoldi_at_mpifr-bonn.mpg.de

Dr. Wilhelm Altenhoff
Tel.:+49 - 228 - 525-293
Fax:+49 - 228 - 525-229
e-mail: waltenhoff_at_mpifr-bonn.mpg.de

Dr. Norbert Junkes (MPIfR public outreach)
Fax: +49 - 2257 - 301-105
e-mail: njunkes_at_mpifr-bonn.mpg.de

Press Release: 7 October 2002

PRI (MPIfR) 10/02 (2)

Beyond Pluto: Max-Planck radioastronomers measure the sizes
of distant minor planets

Scientists at the Max-Planck-Institute for Radioastronomy
(MPIfR) in Bonn were able to determine the diameters of four
of the five largest and most distant minor planets in our
solar system. The largest of them was discovered last June
by planetary scientists of the California Institute of
Technology (Caltech), who named their object "Quaoar" after
a creation myth of the Californian native Tongva people.
The radio observations of the Bonn astronomers and their
Californian colleagues show that Quaoar has a diameter of
1250 km, making it the largest object discovered in the
solar system since the discovery of Pluto in 1930.

Minor planets are usually discovered as slowly moving
unresolved sources in optical sky photographs taken with
astronomical telescopes. Drs. Frank Bertoldi and Wilhelm
Altenhoff from the MPIfR recently used the IRAM 30-meter
telescope in Spain to measure the thermal radiation of
four of the optically brightest minor planets. From the
measured intensity they could derive their sizes, which
range between 700 and 1200 km (see table below). On October
7 their Caltech colleagues presented their discovery of
Quaoar at the annual meeting of the Planetary Sciences
Division of the American Astronomical Society, which is
held in Birmingham, Alabama. There they also present a
direct size measurement of Quaoar from optical images
obtained with the Hubble Space Telescope. This unique and
first such observation confirms the prior radio size
measurement.

The four minor planets are members of a ring of some 100,000
objects in the outskirts of the solar system, beyond Pluto
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 mid of last century, the
existence of a ring of small planetisemals was first
suggested by the astronomers Kenneth Edgeworth (1880-1972)
and Gerard P. Kuiper (1905-1973), but the first discovery
of an "Edgeworth-Kuiper belt object" (EKO) was not until
1992. By now, over 550 EKOs are known.

A direct size determination of an EKO had not been possible
until recently due to the large distance of these small
objects. However, using the IRAM 30-m telescope and MAMBO,
a very sensitive heat sensor built at the MPIfR in Bonn,
the Bonn scientists were able to measure the very weak
thermal radiation emerging from the four large EKOs.

"The velocity with which a distant solar system object
moves reveals its distance," explains Dr. Frank Bertoldi.
"From that we can compute the objects' surface temperature,
which is mostly given by the solar irradiation. The
intensity of the heat radiation we receive from the EKO
depends on its distance, temperature, and size, so knowing
the distance and temperature, we find its size. On the
other hand, the optical brightness of the object, which is
simply reflected sunlight, does not tell us much about its
size, because the very low surface reflectivity may vary
significantly from object to object."

"The discovery of two large EKOs by our American colleagues
this year is impressive and important," admits Dr. William
Altenhoff, who has researched minor planets and comets for
decades. "In the coming years I expect the discovery of
many more and even larger of such objects. What is
interesting to us is to find out the extend of the Kuiper
belt, and particularly what the total mass of all the EKOs
together might be. This would allow unique insights into
the origin of our solar system. The EKOs are the debris
from its formation, an archeaological site containing
prestine remnants of the solar nebula, from which the sun
and the planets formed. A determination of the size and
reflectivity of some of the EKOs enables us to estimate
also the total mass of the many smaller EKOs, which are
too small to measure their individual sizes."

The observations at millimeter wavelengths were made using
the IRAM 30-meter telescope at Pico Veleta near Granada in
Spain (Fig. 2). The sensitive bolometer detector MAMBO
(Fig. 3) used here 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 Geografico Nacional.


The five largest Edgeworth-Kuiper-Belt objects known

[NOTE: Original table is at
http://www.mpifr-bonn.mpg.de/staff/bertoldi/kbo/pr_kbo_e.html]

Name Solar Diameter Reflec- measured by using
        distance tivity

Quaoar 42 au 1250 +/- 12% Brown, Trujillo HST
                     50 km
                    1200 +/- Bertoldi, Brown, IRAM 30m
                     200 km Trujillo, Margot
                                            

Ixion 43 au 1055 +/- 9% Altenhoff, IRAM 30m
(2001KX76) 165 km Bertoldi

Varuna 43 au 900 +/- 7% Jewitt, Aussel, JCMT
                      140 km Evans

2002AW197 48 au 890 +/- 10% Margot, Brown, IRAM 30m
                      120 km Trujillo, Bertoldi

1999TC36 31 au 675 +/- 3.5% Altenhoff, IRAM 30m
                      100 km Bertoldi

Remarks:

* JCMT = James-Clerk-Maxwell Teleskop, Hawaii
* HST = Hubble Space Telescope
* au = "astronomical unit" = average earth-sun distance,
       ca. 150 million km.
* Ixion: Greek mythology, a Thesalian king who was tied to a
  wheel as punishment for advancing Hera


Further information on the internet:

* Discovery of Quaoar by Mike Brown und Chad Trujillo
  http://www.gps.caltech.edu/~chad/quaoar/
* Size determination of 2002AW197
  http://www.gps.caltech.edu/%7Emargot/posters/dps02.jpg
* Hubble Space Telescope size determination of Quaoar
  http://oposite.stsci.edu/pubinfo/PR/2002/17/pr.html
* Annual meeting of the Division for Planetary Sciences of the
  American Astronomical Society
  http://csem.engin.umich.edu/dps/
* David Jewitt's Kuiper Belt Page
  http://www.ifa.hawaii.edu/faculty/jewitt/kb.html
* MPIfR Bonn
  http://www.mpifr-bonn.mpg.de/
* MAMBO detector
  http://www.mpifr-bonn.mpg.de/staff/bertoldi/mambo/
* IRAM 30m telescope
  http://www.iram.es/
* Website of the Tongva people
  http://www.tongva.com/

IMAGE CAPTIONS:

[Figure 1:
http://www.mpifr-bonn.mpg.de/staff/bertoldi/kbo/vergleich-e1.jpg (26KB)]
The newly discovered EKO Quaoar, compared in size with Pluto,
the Moon, and Earth. (image credit: NASA)

[Figure 2:
http://www.mpifr-bonn.mpg.de/staff/bertoldi/kbo/iram30m.jpg (15KB)]
The IRAM 30-m radio telescope in the Spanish Sierra Nevada,
near Granada.

[Figure 3:
http://www.mpifr-bonn.mpg.de/staff/bertoldi/kbo/mambo.jpg (17KB)]
The Max-Planck-Millimeter-Bolometer (MAMBO) 37-element array
detector for observations at millimeter wavelengths. The
physical diameter of the hexagonal horn array is ca. 4 cm.
Received on Tue 08 Oct 2002 06:19:16 PM PDT