From: Amara Graps (Amara.Graps@mpi-hd.mpg.de)
Date: Fri May 17 2002 - 10:22:40 MDT
Institute for Astronomy
University of Hawaii
Honolulu, Hawaii
Contacts:
Dr. David Jewitt, 808-956-7682, jewitt@ifa.hawaii.edu
Mr. Scott S. Sheppard, 808-956-6098, sheppard@ifa.hawaii.edu
Mrs. Karen Rehbock, 808-956-6829, rehbock@ifa.hawaii.edu
Web Site:
http://www.ifa.hawaii.edu/~sheppard/satellites/jup.html
FOR IMMEDIATE RELEASE: May 16, 2002
UH Astronomers Announce Discovery of 11 New Satellites of Jupiter
Summary
University of Hawaii astronomers announce the discovery of 11 new
satellites of Jupiter. These new satellites, when added to the
eleven discovered the previous year by the Hawaii team, bring the
total of known Jupiter satellites to 39. This is more than any other
planet.
Discoveries
The new satellites were discovered during mid-December of 2001 by a
team led by Scott S. Sheppard and David Jewitt from the University
of Hawaii's Institute for Astronomy and including Jan Kleyna of
Cambridge University, England. They used the Canada-France-Hawaii
(3.6 meter) telescope with one of the largest digital imaging
cameras in the world, the "12K", to obtain sensitive images of a
wide area around Jupiter. The digital images were processed using
high speed computers and then searched with an efficient computer
algorithm. Candidate satellites were monitored in the succeeding
months at the University of Hawaii 2.2-meter telescope to confirm
their orbits and to reject closer asteroids masquerading as
satellites. Orbits of the new satellites were fitted by both Robert
Jacobson at the NASA Jet Propulsion Laboratory and Brian Marsden at
the Minor Planet Center. The satellites were formally announced by
the International Astronomical Union on Circular No. 7900 (May 16,
2002).
Properties
The 11 new objects all belong to the so-called "irregular satellite"
class, meaning that they have large semi-major axes, eccentricities
and inclinations. All are retrograde (they orbit in the direction
opposite to the rotation of the planet), and possess similar
semi-major axes (about 300 Jupiter radii or 20 million km) The
estimated diameters are between about 2 and 4 kilometers, assuming a
4% albedo. As yet, nothing is known about their surface properties,
compositions or densities, but they are presumed to be rocky objects
like the asteroids.
The new discoveries bring the known total of Jupiter satellites to
39, of which 31 are irregulars. (The 8 regular satellites include 4
large objects discovered by Galileo and 4 small objects on circular
orbits interior to that of Io). Jupiter's nearest rival for having
the largest number of known satellites is Saturn, with 30 (of which
13 are irregular).
Significance
The large, elongated and inclined orbits of the irregular satellites
strongly suggest an origin by capture. Since no efficient
contemporary capture mechanisms are known, it is likely that the
irregular satellites were acquired when Jupiter was young, possibly
still in the process of condensing down to its equilibrium size.
The precise mechanism of capture remains unidentified but there
are two leading theories for the capture process. In the gas drag
hypothesis, passing asteroids are slowed by friction with proto-
Jupiter's bloated atmosphere. Those which do not burn up in the
atmosphere like meteors are trapped in looping orbits like those of
the new satellites. In the mass growth hypothesis, the rapid growth
of Jupiter leads to capture of nearby, co-moving planetesimals.
Both processes would have operated in the first million years of
the solar system.
The irregular satellites are grouped into distinct dynamical
families or clusters. This suggests that individual satellites are
pieces of a few precursor bodies that have been shattered. The
disruptions occurred either during the process of capture or
possibly after capture due to collisions with Jupiter-crossing
comets. Future measurements of the size distribution, surface
properties and orbits of the satellites will help determine how
they formed.
The Institute for Astronomy at the University of Hawaii conducts
research into galaxies, cosmology, stars, planets, and the Sun. Its
faculty and staff are also involved in astronomy education, deep
space missions, and in the development and management of the
observatories on Haleakala and Mauna Kea. Refer to
http://www.ifa.hawaii.edu/ for more information about the Institute.
--
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Amara Graps, PhD | Max-Planck-Institut fuer Kernphysik
Heidelberg Cosmic Dust Group | Saupfercheckweg 1
+49-6221-516-543 | 69117 Heidelberg, GERMANY
Amara.Graps@mpi-hd.mpg.de * http://www.mpi-hd.mpg.de/dustgroup/~graps
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"Never fight an inanimate object." - P. J. O'Rourke
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