The team believes the surprising similarities between some micrometeorites landing on Earth and comet samples returned by NASA's Stardust mission are no accident. "There has been lots of debate about the nature of micrometeorites reaching the Earth," says Dr. Matthieu Gounelle of the Museum National d'Histoire Naturelle in Paris. "Some believe they are asteroidal, while others argue they are cometary. Our work suggests that in a sense, both camps may be right."
"Our model shows that comets are relatively easy to break up when hit by something, at least when compared to typical asteroids. It is unavoidable that some of the debris went on to land on asteroids, the Moon, and the Earth. In fact, some of the leftovers may still be arriving today," says Dr. Alessandro Morbidelli of the Observatoire de la Cote d'Azur in Nice, France.
"Some of the meteorites that once resided in the asteroid belt show signs they were hit by 3.5 to 3.9 billion years ago. Our model allows us to make the case they were hit by captured comets or perhaps their fragments," adds Dr. Kleomenis Tsiganis of Aristotle University of Thessaloniki, Greece. "If so, they are telling us the same intriguing story as the lunar samples, namely that the solar system apparently went berserk and reconfigured itself about 4 billion years ago."
The main asteroid belt contains a surprising diversity of objects, from primitive ice/rock mixtures to igneous rocks. The standard model used to explain this assumes that most asteroids formed in place from a primordial disk. The standard model then says that the disk underwent chemical changes within this zone. This new model, however, shows that the observed diversity of the asteroid belt is not a direct reflection of the original composition of the proto-planetary disk. These results fundamentally change our view of the asteroid belt.
Additional tests of this model will come from studies of meteorites, the asteroid belt, planet formation, and the Moon. "The Moon and the asteroid belt may be the best and most accessible places in the solar system to understand this critical part of solar system history," says Levison. "We believe key evidence from these cold airless bodies may help us unlock the biggest 'cold case' of all time."
The animation simulates the first 1.2 billion years of solar system history. The orbits of the 4 giant planets are shown as color ellipses. The green dots show small comet-like objects. A small fraction of these objects become trapped in the asteroid belt when the orbits of the planets become unstable. In the simulation shown, this instability occurs at 880 million years.
(Photo Credit: Southwest Research Institute)
Researchers collected this micrometeorite in the vicinity of CONCORDIA station incentral Antarctica (Dome C, 73°S, 123°E).
(Photo Credit: CSNSM-Orsay-CNRS / IPEV)
Source: Southwest Research Institute