Rare Meteorites Reveal Details Of Solar System’s Ancient Nebula

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Hard and fast details about our solar system’s beginnings are extraordinarily difficult to come by. But a research team using new measurements of pristine magnetic fields within two extremely rare meteorites have successfully modeled a portion of our solar system’s earliest evolution.

A new paper appears in The Journal of Geophysical Research – PlanetsThe article describes new paleomagnetic measurements taken from samples of Antarctic meteorites by Allan Hills, A77307 and Dominion Range, 08006.

And for the first time, magnetic measurements within these meteorites allowed the team to constrain the lifetime and spatial evolution of our solar system’s protoplanetary disk. That is, the rotating disk of gas and dust from which our solar system’s planets first formed some 4.56 billion years ago.

Our study shows that the solar nebula —- the cloud of gas and dust out of which our solar system formed, dissipated very quickly (within less than 1.5 million years) after having lasted for 3 million years, Benjamin Weiss, the paper’s second author and a Professor of Planetary Sciences at MIT, told me. He says that the mechanism that dispersed solar nebula was either heating from the sun’s young light or wind generated by magnetic fields within the disk.

Since long time, researchers have known there was a gap in the solar nebula surrounding what we now refer to as the Main Asteroid Belt. This gap was initially thought to be caused by Jupiter, our gas giant planet. Researchers now have new ideas.

Isotopic data from meteorites point to two reservoirs existing in the early solar system; one of the initial hypotheses was that Jupiter created that gap, Cauê S. Borlina, the paper’s lead author and a Blaustein Postdoctoral Fellow in Earth and Planetary Sciences at Johns Hopkins University, told me. However, he said that there are other examples that show that the gap could be formed by other mechanisms.

“The role of magnetic fields makes sense because we see evidence for it in potentially creating a gap and also driving the dissipation of the nebula,” said Borlina.

MIT says that gas and dust co-emerged on the inner side to form terrestrial planets. This includes the Earth and Mars. MIT notes that Jupiter and other outer gas giants formed at the far end of the gap.

Borlina says that determining the date the solar nebula disappeared sets the time for gas driven planetary migration. It also determines how long giant planets are allowed to grow. This is because they grow by adding gas. This helped the team understand what mechanisms were responsible for the nebula’s disappearance.

What was the team’s biggest challenge?

Weiss says that it is difficult to find the right samples for study. These two meteorites are similar to needles in a maze. They are two of the most well-preserved early solar system samples. He says that these meteorites were formed 4.5 billion year ago and experienced very little heating or rusting.

They also had not been hit by very high pressures, and thus wouldn’t have been re-magnetized which can remove the “primary” solar nebula record, says Borlina. Borlina says that once we have selected the samples, we can slice them into pieces of approximately a few millimeters. To measure the samples, we use a magnetometer.

What is the most surprising thing about your results?

Our solar nebula experienced a strong magnetic field for the first 3,000,000 years of the solar system’s history. This was similar to the current Earth’s magnetic strong field. He says that suddenly the magnetic field disappeared and the gas vanished in a matter of seconds across the entire inner solar system. This was at 7 Astronomical Units (Earth Sun distances).

What’s next?

Our next step is to measure the magnetic field at the very beginning of the solar system from measurements of calcium-aluminum-rich inclusions, the oldest known solids, says Weiss. He says that we can determine how long the nebula lasted, and how fast it disappeared at different locations to help us understand how the planets were formed.

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