NASA's Wide-field Infrared Survey Explorer, WISE, has uncovered new clues about the Jovian Trojans - asteroids that orbit the sun on the same path as Jupiter in two 'packs'.
It's the first time that astronomers have been able to take a detailed look at the Trojans' colors. Both the leading and trailing packs turn out to be made up of predominantly dark, reddish rocks with a matte, non-reflecting surface. What's
They've also found that the leading pack of Trojans outnumbers the trailing set.
The two groups of rocks are strikingly similar, says NASA, and don't harbor any interlopers from other parts of the solar system. They don't 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.
"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," says WISE scientist Tommy Grav.
"Later, Jupiter re-captured 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."
The team has analyzed the colors of 400 Trojan asteroids so far, allowing many to be properly sorted according to asteroid classification schemes for the first time.
"We didn't see any ultra-red asteroids, typical of the main belt and Kuiper belt populations," says Grav.
"Instead, we find a largely uniform population of what we call D-type asteroids, which are dark burgundy in color, with the rest being C- and P-type, which are more grey-bluish in color. More research is needed, but it's possible we are looking at the some of the oldest material known in the solar system."