How did the infant sun form? Scientists get surprising new insights from 4.6-billion-year-old space dust
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New research suggests that dust from meteorites contains a “fossil record” dating back to the formation of the sun. The research reveals that magnetism played a far greater role in the birth of the solar system than had previously been suspected.
Around 4.6 billion years ago, the solar system was a cloud of gas and dust, known as a solar nebula. Over the next few million years, this cloud began to flatten, forming a donut-shaped ring or torus with a budding star gathering mass at its core. Eventually, planets would form within this so-called protoplanetary disk.
Scientists have always theorized that gravity was the main sculptor during this early era. But the new study suggests that gravity had major assistance from magnetism. The signature of this additional cosmic artist was found within grains of dust sealed in DOM 08006, a meteorite recovered from Antarctica in 2008.
The grains found by the team are calcium-aluminum-rich inclusions (CAIs), which are thought to have formed during the first 200,000 years of the solar system. That potentially makes them the oldest samples of solar system material ever seen.
“We know they are the oldest things we have of the early solar system,” team leader Cauê Borlina of Purdue University said in a statement. “But CAIs are very complex and are not all the same, even within a 1-millimeter piece of the meteorite. So we have to carefully identify what types they are.”
These CAIs indicated that there was a magnetic field in the proto-solar system even during its solar nebula phase. This magnetic field would have been stronger than Earth’s magnetosphere and, as such, would have influenced the flattening of the solar nebula.
“This transition, from a spherical cloud to a protoplanetary disk, is one of the most significant events in all of solar system history,” team member Benjamin Weiss, of the Massachusetts Institute of Technology (MIT), said in the same statement. “It has long been theorized that gravity caused this, but our measurements show magnetism likely played a role.”
A new spin on early solar system magnetism
In the newly forming solar system, a magnetic field would have been generated when charged particles were sent spinning through the collapsing cloud of gas and dust that birthed the sun. This plasma would then have sustained that field.
As such, that magnetism must have affected the material in the solar nebula that would become the solar system. For that reason, the team reasoned that the strength of this field should be “locked in” to materials from the time as remanent magnetization. This matter could make its way to Earth in meteorites.
In fact, the same scientists who conducted this research previously found evidence of a magnetic field that existed 2 million years into the formation of the solar system, baked into meteorites. That’s an impressive and important find, because this magnetic field would have helped planets like Earth form — but the sun was already around by that point. Thus, the team was after an earlier magnetic field, one that predated our star.
“Nowadays, people don’t debate whether magnetism is present when planets are forming. But the debate is around the very early solar system, before planets are forming, when there’s just a disk,” Borlina said. “That’s where the debate still resides, and that’s where we’re operating now.”
DOM 08006 is one of the most unspoiled or “primitive” meteorites ever discovered, retaining and preserving materials, including CAIs, as they were when the sun was forming.
“Other meteorites went through many different processes over this 4.5 billion-year history,” said Weiss. “They were formed in the solar nebula, then added to bodies with water, then got destroyed, moved to the asteroid belt, and then landed here. But somehow, DOM has experienced less alteration than any other meteorite.”
If a magnetic field existed during the earliest stage of the solar system, it should be observable in the matter that makes up DOM 08006.
The team was able to isolate and identify a handful of CAIs that contained inherently magnetic minerals such as iron, which they tested to measure any magnetism they had retained.
Studying these grains, the researchers found evidence of a magnetic field 12 times stronger than that of Earth. They think this magnetic field may have played a crucial role in the evolution of the solar system.
“We think these kinds of magnetic fields were helping to move gas from the protoplanetary disk inward toward this central star, the sun,” Borlina said. “Gravity is also playing a role. But we are now showing that, if you want to fully understand how the sun and planets formed, you should include magnetic fields in the ingredients that make them.”
The new study was published Aug. 7 in the journal Proceedings of the National Academy of Sciences.
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