Wind the cosmic clock back a few billion years and our Solar System looked much different than it does today. About 4.5 billion years ago, the young Sun shone much like it does now, though it was a little smaller. Instead of being surrounded by planets, it was ensconced in a swirling disk of gas and dust. That disk is called a protoplanetary disk and it’s where the planets eventually formed.

There was a conspicuous gap in the early Solar System’s protoplanetary disk, between where Mars and Jupiter are now, and where the modern-day asteroid belt sits. What exactly caused the gap is a mystery, but astronomers think it’s a sign of the processes that governed planet formation.

A group of scientists have published a paper outlining the discovery of this ancient gap. The lead author is Cauê Borlina, a Planetary Science Ph.D. student in the Department of Earth, Atmospheric, and Planetary Sciences (EAPS) at the Massachusetts Institute of Technology (MIT). The title of the paper is “Paleomagnetic evidence for a disk substructure in the early solar system.” It’s published in the journal Science Advances.

Thanks to facilities like the Atacama Large Millimeter/sub-Millimeter Array (ALMA), astronomers are getting better at looking at younger solar systems that still have protoplanetary disks and are still forming planets. They often have conspicuous gaps and rings that are evidence of planets forming. But how exactly it all works is still a mystery.

“Over the last decade, observations have shown that cavities, gaps, and rings are common in disks around other young stars,” says Benjamin Weiss, study co-author and professor of planetary sciences in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS). “These are important but poorly understood signatures of the physical processes by which gas and dust transform into the young sun and planets.”

ALMA’s best image of a protoplanetary disk to date. This picture of the nearby young star TW Hydrae reveals the rings and gaps in young disks. Credit: S. Andrews (Harvard-Smithsonian CfA); B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO)
This ALMA image of the protoplanetary disk around the nearby young star TW Hydrae reveals the rings and gaps in young disks. Credit: S. Andrews (Harvard-Smithsonian CfA); B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO)

The evidence for a gap in our own Solar System’s protoplanetary disk some 4.5 billion years ago comes from the study of meteorites.

The Solar System’s magnetic fields had an effect on the structure of meteorites. The paleomagnetism shaped the tiny rocks in the protoplanetary disk called chondrules. Chondrules are molten or partially molten pieces of round rock that became accreted to a type of meteorite called chondrites. And chondrites are some of the oldest rocks in the Solar System.

As the chondrules cooled they retained a record of the magnetic fields at the time. Those magnetic fields change over time as the protoplanetary disk evolves. The orientation of the electrons in the chondrules is different depending on the nature of the magnetic fields at the time. Collectively, all those chondrules in all those chondrites tell a tale.

This is an image of a chondrite named NWA 869 (Northwest Africa 869) found in the Sahara Desert in the year 2000. There are both metal grains and chondrules visible in the cut face. Image Credit: By H. Raab (User: Vesta) - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=226918
This is an image of a chondrite named NWA 869 (Northwest Africa
Did you miss our previous article…
https://www.mansbrand.com/primordial-gravitational-waves-continue-to-elude-astronomers/

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