A larger nursery for the first solids formed in the solar system

By studying the isotopic variations of the elements vanadium (V) and strontium (Sr), an international team of researchers including scientists from Lawrence Livermore National Laboratory has discovered that these variations are not caused by irradiation from the sun but are produced by condensation and evaporation reactions in the early solar system. The research appears in the September 29 edition of Scientists progress.

“It turns out that some of the short-lived radioactive isotopes that researchers previously believed to be products of early active sun irradiation are more likely to be inherited from our parent molecular cloud, which in turn tells us. long on the cosmic neighborhood. we grew up, “said Greg Brennecka, LLNL cosmochemist, co-author of the article.

The calcium-aluminum-rich (CAI) inclusions in meteorites are the oldest dated solids that formed in the solar system. They contain crucial information regarding the environmental conditions of the early stages of the protoplanetary disc before the formation of any of the planets. This research also suggests that the oldest solids in our solar system may have formed further from the sun than previously thought, with far-reaching implications for the dynamic structure of the nascent solar system.

“Our results indicate that the formation of CAI during molecular cloud collapse and disk build-up likely occurred at greater distances from the sun than we previously thought, potentially to regions forming planets of the solar system, ”said LLNL postdoc Quinn Shollenberger, co-author of the article.

Astronomical observations of young stellar objects indicate that their surrounding accretion disks are directly exposed to levels of high-energy X-ray and particle emissions that are several orders of magnitude higher than those observed for most stars. of the main sequence. However, the duration and characteristics (gradual or impulsive eruptions) of these early stages of strong stellar activity remain poorly understood.

Abnormal abundances of short-lived radionuclides in the CAIs of carbonaceous chondrite meteorites have been suggested as a fossil record of the irradiation of dust by solar cosmic rays at the inner edge of the protoplanetary disk. But the new research overturns this theory. “Knowing where IACs formed is crucial to understanding the distribution and evolution of dust forming planets in the nascent solar system,” according to David Bekaert, lead author of the study.

These refractory inclusions are present in objects that have formed in various parts of the solar system, and have even been found in comets that have formed very far from the sun. If the IACs originally formed very close to the sun, this tells scientists that there was a very vigorous and rapid mixing throughout the protoplanetary disk. However, if these objects only formed in regions of planet formation farther from the sun, as the recent article by Bekaert and colleagues suggests, then much less radial mixing must have taken place.

“Basically it gives us an idea of ​​how high the mixer was turned on. The speed of this mixer is important in understanding how materials moved around the early solar system and why the solar system is laid out that way ( gas giants on the outside, terrestrial bodies on the inside), ”Brennecka said. “This study considerably relaxes the area in which the first solids of the solar system could have formed.”

LLNL scientist Ben Jacobsen as well as researchers from the Woods Hole Oceanographic Institution, the University of Münster, the University of California Los Angeles, the Goethe Universität, the University of Durham and the National Museum of Natural History contributed to this work.