Around 4.567 billion years ago, our Solar System harbored a gap within the protoplanetary disk, near the location where the main asteroid belt resides today, and likely shaped the composition of the planets, according to a study led by MIT scientists.
“Over the last decade, observations have shown that cavities, gaps, and rings are common in disks around other young stars,” said Professor Benjamin Weiss, a researcher in the Department of Earth, Atmospheric, and Planetary Sciences at MIT.
“These are important but poorly understood signatures of the physical processes by which gas and dust transform into the young Sun and planets.”
Over the last decade, planetary scientists have observed a curious split in the composition of meteorites.
These space rocks originally formed at different times and locations as the Solar System was taking shape.
Those that have been analyzed exhibit one of two isotope combinations. Rarely have meteorites been found to exhibit both — a conundrum known as the isotopic dichotomy.
Scientists have proposed that this dichotomy may be the result of a gap in the early Solar System’s disk, but such a gap has not been directly confirmed.
Professor Weiss and colleagues analyze meteorites for signs of ancient magnetic fields.
As a young planetary system takes shape, it carries with it a magnetic field, the strength and direction of which can change depending on various processes within the evolving disk.
As ancient dust gathered into grains known as chondrules, electrons within chondrules aligned with the magnetic field in which they formed.
Chondrules can be smaller than the diameter of a human hair, and are found in meteorites today.
The researchers specializes in measuring chondrules to identify the ancient magnetic fields in which they originally formed.
In previous work, they analyzed samples from one of the two isotopic groups of meteorites, known as the noncarbonaceous meteorites.
These rocks are thought to have originated in a reservoir, or region of the early Solar System, relatively close to the Sun.
They previously identified the ancient magnetic field in samples from this close-in region.
In the new study, they wondered whether the magnetic field would be the same in the second isotopic, carbonaceous group of meteorites, which, judging from their isotopic composition, are thought to have originated farther out in the Solar System.
They analyzed chondrules, each measuring about 100 microns, from two carbonaceous meteorites that were discovered in Antarctica.
Using the superconducting quantum interference device (SQUID), they determined each chondrule’s original, ancient magnetic field.
Surprisingly, they found that their field strength was stronger than that of the closer-in noncarbonaceous meteorites they previously measured.
As young planetary systems are taking shape, scientists expect that the strength of the magnetic field should decay with distance from the Sun.
In contrast, the authors found the far-out chondrules had a stronger magnetic field, of about 100 microteslas, compared to a field of 50 microteslas in the closer chondrules. For reference, the Earth’s magnetic field today is around 50 microteslas.
一个行星系统的磁场是一个衡量of its accretion rate, or the amount of gas and dust it can draw into its center over time
Based on the carbonaceous chondrules’ magnetic field, the Solar System’s outer region must have been accreting much more mass than the inner region.
Using models to simulate various scenarios, the team concluded that the most likely explanation for the mismatch in accretion rates is the existence of a gap between the inner and outer regions, which could have reduced the amount of gas and dust flowing toward the sun from the outer regions.
“差距行星系统中很常见,我们now show that we had one in our own Solar System,” said Cauê Borlina, a graduate student in the Department of Earth, Atmospheric and Planetary Sciences at MIT.
“This gives the answer to this weird dichotomy we see in meteorites, and provides evidence that gaps affect the composition of planets.”
Thefindingswere published in the journalScience Advances.
Cauê S. Borlinaet al. 2021. Paleomagnetic evidence for a disk substructure in the early Solar System.Science Advances7 (42); doi: 10.1126/sciadv.abj6928