"The other is that winds in the inner solar system could have lofted particles over the Jupiter gap."Įither of these mechanisms could also be responsible for inner solar system material that has also been found in comets by the Stardust mission. "One is that there was still movement along the disk midplane, although it should have been stopped by Jupiter," he said. How? There are a couple of possible mechanisms, Williams said. Some material from the inner solar system must have managed to cross the Jupiter barrier to accrete with outer solar system chondrules into a meteorite that billions of years later would fall to Earth. These meteorites turned out to contain chondrules from both the inner and outer solar system. Then they studied individual chondrules from two chondritic meteorites, the Allende meteorite that fell in Mexico in 1969 and the Karoonda meteorite, which fell in Australia in 1930. They confirmed that they fell into two distinct groups: the non-carbonaceous chondrites as well as other, more common types of meteorite and the carbonaceous meteorites. Yin, UC Davis research scientist Curtis Williams, and their collaborators carried out a detailed study of isotopes from 30 meteorites. Yet some meteorites seem to be exceptions to this general rule with a wider mixture of components. Astronomers using the ALMA radio telescope in Chile have observed the same phenomenon in protoplanetary disks around other stars. Why was there not more mixing, if all the planets formed from the same protoplanetary disk? The explanation is that as Jupiter formed earlier, it plowed a gap in the disk, creating a barrier to the movement of dust, Yin said. Non-carbonaceous meteorites formed from the disk closer to the sun where carbon-based and other volatile compounds were baked away. Carbonaceous meteorites are thought to have originated in the outer solar system. Previous work by Yin's laboratory and others showed that meteorites fall into two broad groups by composition. Researchers can work out approximately where and when these meteorites formed by measuring the ratios of isotopes of elements such as oxygen, titanium and chromium within them. Further evidence comes from rocks from the Earth and Moon and samples of cosmic dust and comet material collected by the Stardust mission and other space probes. The material in chondrites is extremely old, representing leftover dust and debris that from the very early solar system. "If we understand transport, we can understand the properties of the disk and infer how the planets were built," said Qingzhu Yin, professor of earth and planetary sciences at the University of California, Davis and coauthor on the paper. Evidence for the composition of this protoplanetary disk in our own solar system comes from chondrites, a type of meteorite made up of smaller particles, or chondrules, that collected together like a cosmic dust bunny. The consensus theory on how planets form is that they accrete from a disk of dust and gas that rotates around a new-formed star.
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