[meteorite-list] Three New 'Trojan' Asteroids Found Sharing Neptune's Orbit

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Jun 15 21:23:07 2006
Message-ID: <200606160120.SAA21594_at_zagami.jpl.nasa.gov>

http://www.carnegieinstitution.org/neptune_trojans/default.html

Carnegie Institution of Washington News Release
Thursday, June 15, 2006

Carnegie Contact: Dr. Scott Sheppard; sheppard_at_dtm.ciw.edu
or (202) 270-0243
Gemini Observatory Contact: Dr. Chadwick Trujillo; trujillo_at_gemini.edu

For a copy of the paper contact Science at scipak_at_aaas.org, or
(202) 326-6440

Three new "Trojan" asteroids found sharing Neptune's orbit

Washington, DC - Three new objects locked into roughly the same orbit as
Neptune - called "Trojan" asteroids - have been found by researchers from
the Carnegie Institution's Department of Terrestrial Magnetism (DTM) and
the Gemini Observatory. The discovery offers evidence that Neptune, much
like its big cousin Jupiter, hosts thick clouds of Trojans in its orbit,
and that these asteroids probably share a common source. It also brings
the total of known Neptune Trojans to four.

"It is exciting to have quadrupled the known population of Neptune
Trojans," said Carnegie Hubble Fellow Scott Sheppard, lead author of the
study, which appears in the June 15 online issue of Science Express. "In
the process, we have learned a lot both about how these asteroids become
locked into their stable orbits, as well as what they might be made of,
which makes the discovery especially rewarding."

The recently discovered Neptune Trojans are only the fourth stable group
of asteroids observed around the Sun. The others are the Kuiper Belt
just beyond Neptune, the Jupiter Trojans, and the main asteroid belt
between Mars and Jupiter. Evidence suggests that the Neptune Trojans are
more numerous than either the asteroids in the main belt or the Jupiter
Trojans, but they are hard to observe because they are so far away from
the Sun. Astronomers therefore require the largest telescopes in the
world equipped with sensitive digital cameras to detect them.

Trojan asteroids cluster around one of two points that lead or trail the
planet by about 60 degrees in its orbit, known as Lagrangian points. In
these areas, the gravitational pull of the planet and the Sun combine to
lock the asteroids into stable orbits synchronized with the planet.
German Astronomer Max Wolf identified the first Jupiter Trojan in 1906,
and since then, more than 1800 such asteroids have been identified
marching along that planet's orbit. Because Trojan asteroids share a
planet's orbit, they can help astronomers understand how planets form,
and how the solar system evolved.

Researchers theorized that Trojans might also flank other planets, but
evidence for this has surfaced only recently. In 2001, the first Neptune
Trojan was spotted in the planet's leading Lagrangian point. In 2004,
Sheppard and Chadwick Trujillo of the Gemini Observatory, who is also an
author on the current study, found the second Neptune Trojan using
Carnegie's Magellan-Baade 6.5 meter telescope in Las Campanas, Chile.
They found two more in 2005, bringing the total to four, and observed
them again using the 8-meter Gemini North telescope on Mauna Kea in
Hawaii in order to accurately determine their orbits. All four of the
known Neptune Trojans reside in the planet's leading Lagrangian point.

One of the new Trojans has an orbit that is more steeply tilted to the
plane of the solar system than the other three. Although only this one
has such a steep orbit, the methods used to observe the asteroids are
not sensitive to objects so far out of tilt with the rest of the solar
system. The very existence of this Trojan suggests that there are many
more like it, and that Neptune's Trojans as a whole occupy thick clouds
with complex, interlaced orbits.

"We were really surprised to find a Neptune Trojan with such a large
orbital inclination," Trujillo said. "The discovery of the one tilted
Neptune Trojan implies that there may be many more far from the solar
system plane than near the plane, and that the Trojans are really a
'cloud' or 'swarm' of objects co-orbiting with Neptune."

A large population of high-inclination Neptune Trojans would rule out
the possibility that they are left over from early in the solar system's
history, since unaltered primordial asteroid groups should be closely
aligned with the plane of the solar system. These clouds probably formed
much like Jupiter's Trojan clouds did: once the giant planets settled
into their paths around the Sun, any asteroid that happened to be in the
Trojan region "froze" into its orbit.

Sheppard and Trujillo also compared, for the first time, the colors of
all four known Neptune Trojans. They are all about the same shade of
pale red, suggesting that they share a similar origin and history.
Although it is hard to tell for sure with only four on the books, the
researchers believe that the Neptune Trojans might share a common origin
with the Jupiter Trojans and outer irregular satellites of the giant
planets. These objects might be the last remnants of the countless small
bodies that formed in the giant planet region, most of which eventually
became part of the planets or were tossed out of the solar system.

------------------------------------------------------------------------

This paper includes data gathered with the Carnegie 6.5 meter Magellan
Telescopes located at Las Campanas Observatory, Chile, and is based in
part on observations obtained at the 8-meter Gemini North telescope on
Mauna Kea in Hawaii. Funding for the work was provided by NASA and the
Gemini partnership, which includes: the National Science Foundation
(United States), the Particle Physics and Astronomy Research Council
(United Kingdom), the National Research Council (Canada), CONICYT
(Chile), the Australian Research Council (Australia), CNPq (Brazil) and
CONICET (Argentina).

The Carnegie Institution of Washington (www.carnegieinstitution.org>
has been a pioneering force in basic scientific research since 1902.
It is a private, nonprofit organization with six research departments
throughout the U.S. Carnegie scientists are leaders in plant biology,
developmental biology, astronomy, materials science, global ecology,
and Earth and planetary science.
Received on Thu 15 Jun 2006 09:20:16 PM PDT