When does the sun blow away the solar nebula?
The story of the origin of our solar system is quite well known. It reads like this: The sun began as a protostar in the “solar nebula” more than 4.5 billion years ago. Over the course of several million years, the planets emerged from this nebula and disappeared. Of course, the devil is in the details. For example, how long exactly did the protoplanetary disk that gave birth to the planet last? A paper was recently submitted to Geophysical Research Journal take a closer look at the planet-born crèche. In particular, it shows how the magnetism of the meteorite helps tell the story.
About That Solar Nebula
About 5 billion years ago, the environment of our galaxy was a nebula made of hydrogen gas and some dust. It provided the seeds of what became our solar system. Somehow, this part of the molecular cloud started to clump together on its own. Perhaps a passing star sent shockwaves and ripples through the dust and caused it to compress. Or, maybe a nearby supernova did. Whatever happened, it started the process of birth of the protostar that eventually became the Sun.
During the birth process, baby Sun in his birth crêche goes through what is called the T Tauri phase. It blew extremely hot winds filled with protons and neutral helium atoms into space. At the same time, some matter is still falling onto the star.
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While all this was happening, the cloud moved and flattened out like a pancake. Think of it like an accretion disk that feeds material into the center where stars form. It is not only filled with planetary seeds, but also woven with magnetic fields. This active disk is where the planets form. They started out as lumps of dust, which stuck to each other into pebbles the size of a rock. The rocks collide with each other to form larger and larger conglomerates called planetesimals. They, in turn, collided and formed planets. That’s the executive summary of the formation of the solar system. But, to get more details, scientists have to dig a little deeper.
Studying the Rocks of the Solar Nebula
After the planets are born, what happens to the rest of the nebula? In 2017, planetary scientist Huapei Wang and collaborators reported on their study of meteorites dating from that time. They found that the solar nebula had been cleared about four million years after the formation of the solar system.
A team of scientists, led by Cauê S. Borlina of Johns Hopkins University and MIT, wondered if the system disappeared all at once. Or, did it happen in two different timescales? To answer that, the team turned to a characteristic called “solar nebula paleomagnetism”. That’s a nice way of saying that there is a magnetic field in the nebula. Meteoroids that formed in the nebula at that time (called carbonaceous chondrites) contain traces of that field. Borlina and team speculate that there is one schedule for the inner solar system and one for the outer regions. But, how to know with certainty the schedule? The traces of the magnetic field hold several clues.
The rock that formed in the nebula should show traces of a magnet that reflected the magnetic field at the time. Those that form after the nebula is cleared won’t show many (or any) magnetic fingerprints. They will record the magnetism (or lack thereof) of that time and place.
Magnetism in Primordial Rocks
Borlina’s team studied meteorites found in Antarctica in late 1977/78 and 2008. The rocks are made of a primordial material called “carbon chondrite” that formed early in the history of the solar system. The team focused on the magnetite (iron oxide mineral) found in each sample. Magnetite “records” the so-called “remanent magnetization” imposed by the presence of a local field. Then, they compared other paleomagnetic studies of certain unmagnetized rocks called “angrites”. Presumably, it formed after the solar nebula (and its intrinsic magnetic field) had disappeared.
Further analysis provided a time frame for cleaning up the inner and outer solar systems. For the inner region—1-3 AU, from roughly Earth’s orbit to the outer boundary of the Asteroid Belt—the team found nebula dissipation occurred about 3.7 million years after the formation of the solar system. The outer solar system will take another 1.5 million years to clean up.
That’s the square of the previous estimate of about 4 million years for a complete sweep. The next step is to get a more precise age of the average meteorite. That would help scientists place some more definite boundaries on the actual dissipation timeline. In particular, the team would like to do more experimental work on magnetite samples in these various chondrite families. That would let them know exactly when the rocks had picked up the traces of the magnetic field.
Implications for Other Solar Systems
The idea of using rock to “strip off” the solar nebula and its dissipation has implications for protoplanetary disks around other stars. This suggests that most such disks undergo the evolution of two timescales. Combine that with previous research showing that the protoplanetary disk had a substructure, and we now have even more insight into the chaotic conditions shortly after the birth of our Sun and planet.
For more information
Lifetime of the Outer Solar System Nebula From Carbonated Chondrite
Paleomagnetic Evidence for Disk Substructures in the Early Solar System
Lifespan of Solar Nebula Limited by Meteorite Paleomagnetism
#sun #blow #solar #nebula
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