The asteroids are unusual in that they travel in packs, with one group leading the way along the orbit in front of the gas giant planet, with a second group trailing behind.
Data from NASA's Wide-field Infrared Survey Explorer has revealed details of the Trojans' colors, important clues to their composition and origin, NASA's Jet Propulsion Laboratory in Pasadena, Calif., reported Monday.
The findings suggest the Trojans do not resemble the asteroids from the main belt between Mars and Jupiter, nor the Kuiper belt family of objects from the icier, outer regions near Pluto, astronomers said.
"Jupiter and Saturn are in calm, stable orbits today, but in their past, they rumbled around and disrupted any asteroids that were in orbit with these planets," said Tommy Grav, a WISE scientist from the Planetary Science Institute in Tucson. "Later, Jupiter recaptured the Trojan asteroids, but we don't know where they came from. Our results suggest they may have been captured locally.
"If so, that's exciting because it means these asteroids could be made of primordial material from this particular part of the solar system, something we don't know much about."
Other planets have been found to have Trojan asteroids riding along with them in their orbits, including Mars, Neptune and even Earth, where WISE recently found the first known Earth Trojan.