Posted: September 23, 2008
New analysis of dust from comet Wild 2 is challenging common views about the history and evolution of the Solar System, showing it may be more mixed-up than previously thought.
Cosmic dust grains were collected from comet Wild 2 in 2004 and safely returned to the Earth for analysis two years later as part of NASA’s Stardust mission, the first mission to collect primitive samples of Solar System material from beyond the orbit of the Moon. New analysis of the composition of these tiny grains, led by Tomoki Nakamura of Kyushu University in Japan, suggests an unexpected mingling of rocky material between the centre and edges of the Solar System.
Tiny crystals from the Wild 2 comet, resemble fragments of the molten mineral droplets called chondrules, shown here, found in primitive meteorites. Similar flash-heated particles were found in Wild 2, a comet formed in the icy fringes of outer space, suggesting that solid materials may have been transported outward in the young Solar System. Image: Noriko Kita.
Using an instrument known as an ion microprobe, the science team studied the oxygen isotope ratios of the dust grains, and found them to be more like those found in asteroids and even the Sun itself than those expected from the comet's birth place in the outer reaches of the Solar System.
"This really complicates our simple view of the early Solar System," says Michael Zolensky, a NASA cosmic mineralogist at the Johnson Space Center in Houston.
The results counter the idea that the material that formed the Solar System billions of years ago remained trapped in orbits around the Sun. Instead, cosmic material must be able to migrate outward through the Solar System and mix with the more primitive materials found at the fringes.
"Observations from this sample are changing our previous thinking and expectations about how the Solar System formed," says UW-Madison geologist Noriko Kita. "They [Stardust mission scientists] were originally hoping to find the raw material that pre-dated the Solar System. "However, we found many crystalline objects that resemble flash-heated particles found in meteorites from asteroids."
The findings are causing scientists to rethink their theories of Solar System formation and evolution, showing that complicated movements of material around the Solar System were more likely than not. The results are published in the 19 September edition of the journal Science.