• Web Site: http://www.ifa.hawaii.edu/~sheppard/satellites/jup.html


    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.


    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).


    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.

    Object IAU Name Semi-maj Axis
    [Jup Radii]
    Eccentricity Inclination
    a543509 S/2001 J10 266 0.16 147 534
    a503602 S/2001 J8 291 0.48 165 609
    a542908 S/2001 J9 292 0.27 142 617
    a543208 S/2001 J2 292 0.30 149 615
    a543107 S/2001 J7 293 0.18 146 622
    a506111 S/2001 J3 299 0.25 150 630
    a543104 S/2001 J6 321 0.29 165 715
    a506111b S/2001 J4 327 0.35 150 713
    a506406 S/2001 J11 328 0.29 166 736
    a506601 S/2001 J5 330 0.45 155 732
    a527405 S/2001 J1 334 0.42 152 753

    Object IAU Name Apparent brightness
    in magnitudes
    Estimated Diameter
    in kilometers
    a543509 S/2001 J10 23.1 2
    a503602 S/2001 J8 23.0 2
    a542908 S/2001 J9 23.1 2
    a543208 S/2001 J2 22.3 4
    a543107 S/2001 J7 22.8 3
    a506111 S/2001 J3 22.1 4
    a543104 S/2001 J6 23.2 2
    a506111b S/2001 J4 22.7 3
    a506406 S/2001 J11 22.7 3
    a506601 S/2001 J5 23.0 2
    a527405 S/2001 J1 22.0 4

    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


    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.


    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