Three New "Trojan" Asteroids Found Sharing Neptune's Orbit

Press Release for July 28, 2006

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 in Hilo, Hawaii. 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.

Download the paper in Science here

Discovery images of the high inclination Neptune Trojan 2005 TN53.
Click on the image to find out more. 


"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, 2006 online issue of
Science. "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 main asteroid 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.


Figure caption: In this schematic of the outer solar system, "Trojan"
asteroids can be seen sharing the orbits of Jupiter and Neptune. At
either of two points 60 degrees away from each planet, the
gravitational forces of the planet and the Sun combine to lock the
asteroids into a stable, synchronized orbit. Three new Trojans have
been found in the region ahead of Neptune, bringing the total to four;
the discovery demonstrates that Neptune probably hosts clouds of
Trojans that are more populous than those in Jupiter's orbit.


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. Though 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.

Click Here to learn about the first detected trailing (L5) Neptune Trojan. 


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 Gemini Observatory in Hilo,
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

The Carnegie Institution of Washington (
has been a pioneering force in basic scientific research since
1902. It is a private, nonprofit organization with six research
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global ecology, and Earth and planetary science.


Scott S. Sheppard, Carnegie Institution of Washington, phone 202-478-8854
Chad Trujillo, Gemini Observatory, phone 808-974-2566


Scott S. Sheppard's Home Page
e-mail sheppard at (replace "at" with "@")