Asteroids reveal our solar system's chaotic infancy
The early solar system was more chaotic than previously thought, according to a new, more precise reconstruction of the early history of several asteroids. Before the Earth and other planets formed, the young sun was still surrounded by cosmic gas and dust. Researchers analyzed iron samples from the cores of such asteroids that landed on Earth as meteorites. “Previous scientific studies showed that asteroids in the solar system have remained relatively unchanged since their formation, billions of years ago,” says Alison Hunt, a researcher at ETH Zurich and the National Centre of Competence in Research PlanetS (NCCR PlanetS) and lead author of the paper in Nature Astronomy. But to unlock this archive, the researchers had to thoroughly prepare and examine the extra-terrestrial material. With the help of a mass spectrometer, they measured abundances of different isotopes of these elements.
In the first few million years of our solar system, radioactive decay of isotopes heated the metallic asteroid cores. The results showed that the cooling was rapid and likely occurred due to severe collisions into other bodies, which broke off the insulating rocky mantle of the asteroids and exposed their metal cores to the cold of space. “Our additional measurements of platinum isotope abundances allowed us to correct the silver isotope measurements for distortions caused by cosmic irradiation of the samples in space. “And to our surprise, all the asteroidal cores we examined had been exposed almost simultaneously, within a timeframe of 7. The near simultaneous collisions of the different asteroids indicated that this period must have been a very unsettled phase of the solar system. The team considered different causes by combining their results with those from the latest, most sophisticated computer simulations of the solar system development.
“The theory that best explained this energetic early phase of the solar system indicated that it was caused primarily by the dissipation of the so-called solar nebula,” says coauthor Maria Schönbächler, professor of cosmochemistry at ETH Zurich and NCCR PlanetS member. “This solar nebula is the remainder of gas that was left over from the cosmic cloud out of which the sun was born. While the nebula was still around, it slowed down the objects orbiting the sun in it—similar to how air resistance slows a moving car. “Our work illustrates how improvements in laboratory measurement techniques allow us to infer key processes that took place in the early solar system—like the likely time by which the solar nebula had gone,” Schönbächler says. “Planets like the Earth were still in the process of being born at that time.
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