When the solar system formed billions of years ago, Jupiter created a rip in the disk of dust and gas around the sun, separating the inner solar system from the outer. New data on meteorites show that some space objects have managed to bridge this gap. The findings, published this week in the Proceedings of the National Academy of Sciences, add to new insights into how our solar system formed and how planets form around other stars.
According to the theory of planet formation, they coalesce from a disk of dust and gas that revolves around the newly formed star. Evidence for the composition of this protoplanetary disk in our solar system comes from chondrites, a type of meteorite made up of smaller particles or chondrules.
The material in chondrites is extremely old and consists of the remnants of dust and debris leftover from the very early solar system. Other evidence comes from rocks from the Earth and the Moon, as well as samples of cosmic dust and cometary material collected by the Stardust mission and other space probes.
Researchers can roughly determine where and when these meteorites formed by measuring the isotope ratios of elements such as oxygen, titanium, and chromium.
Previous work by scientists has shown that the composition of meteorites is divided into two large groups. It is believed that carbonaceous meteorites originated outside the solar system. Non-carbon meteorites were formed from a disk closer to the Sun, where carbon and other volatiles were sintered.
Why was there no more mixing if all the planets were formed from one protoplanetary disk? The explanation is that as Jupiter formed, it ripped open the disk, creating a barrier to the movement of dust. Astronomers using the ALMA radio telescope in Chile have observed the same phenomenon in protoplanetary disks around other stars.
However, some meteorites seem to be the exception to this general rule.
Yin, UC Davis researcher Curtis Williams, and a team of scientists conducted a detailed study of the isotopes of 30 meteorites. They then studied the individual chondrules of two chondritic meteorites – the Allende meteorite, which fell in Mexico in 1969, and the Karunda meteorite, which fell in Australia in 1930.
It turned out that these meteorites contain chondrules from both the inner and outer solar systems. Some material from the inner solar system must have managed to cross the Jupiter barrier to fuse with the chondrules of the outer solar system into a meteorite that will fall to Earth billions of years later.
According to Yin, the new research is helping to connect cosmochemistry, planetary science, and astronomy to give a complete picture of planetary formation.