Using data from NASA’s Wide-field Infrared Survey Explorer, or WISE, scientists have uncovered new clues in the ongoing mystery of the Jovian Trojans -- asteroids that orbit the Sun on the same path as Jupiter.
Like racehorses, the asteroids travel in packs, with one group leading the way in front of the gas giant, and a second group trailing behind.
The observations are the first to get a detailed look at the Trojans’ colours: both the leading and trailing packs are made up of predominantly dark, reddish rocks with a matte, non-reflecting surface. What’s more, the data verify the previous suspicion that the leading pack of Trojans outnumbers the trailing bunch.
The new results offer clues in the puzzle of the asteroids’ origins and about what are they made of.
WISE has shown that the two packs of rocks are strikingly similar and do not harbour any “out-of-towners,” or interlopers, from other parts of the solar system.
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.
“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, Ariz.
“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,” Grav stated.
Grav is a member of the NEOWISE team, the asteroid-hunting portion of the WISE mission.
Other planets were later found to have Trojan asteroids riding along with them too, such as Mars, Neptune and even Earth, where WISE recently found the first known Earth Trojan:
Enter WISE, which roared into orbit on Dec. 14, 2009. The spacecraft’s 16-inch (40-centimeter) telescope and infrared cameras scoured the entire sky looking for the glow of celestial heat sources. From January 2010 to February 2011, about 7,500 images were taken every day. The NEOWISE project used the data to catalogue more than 158,000 asteroids and comets throughout the solar system.
“By obtaining accurate diameter and surface reflectivity measurements on 1,750 Jupiter Trojans, we increased by an order of magnitude what we knew about these two gatherings of asteroids,” said Grav.
“With this information, we were able to more accurately than ever confirm there are indeed almost 40 percent more objects in the leading cloud,” he stated.
The NEOWISE team has analysed the colours of 400 Trojan asteroids so far, allowing many of these asteroids 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,” said Grav.
“Instead, we find a largely uniform population of what we call D-type asteroids, which are dark burgundy in colour, with the rest being C- and P-type, which are more grey-bluish in colour. More research is needed, but it’s possible we are looking at the some of the oldest material known in the solar system,” he added.
Scientists have proposed a future space mission to the Jupiter Trojans that will gather the data needed to determine their age and origins.
The results were presented t at the 44th annual meeting of the Division for Planetary Sciences of the American Astronomical Society in Reno, Nev.
Two studies detailing this research are accepted for publication in the Astrophysical Journal.