Space

Ancient outer solar system had a weak magnetic field

Outer solar system: Many concentric rings of gas and dust around a young star with planets and asteroids objects embedded in the rings.
View larger. | Artist’s concept of the gas and dust in a newly-forming planetary system such as our own. Scientists knew that the embedded magnetic field helped form the inner solar system. Now, a new study shows that it also played a part in shaping the outer solar system as well. Image via NASA.
  • Scientists believe an ancient magnetic field helped to form asteroids and planets in the inner solar system billions of years ago. But what about the outer solar system?
  • New MIT-led research suggests the magnetic field in the outer reaches of the early solar system was weaker, but still strong enough to pull in gas and dust. This field might have helped shape the outer solar system, including the giant planets.
  • Scientists base their claims on tiny grains from the asteroid Ryugu. Japan’s Hayabusa2 mission brought the samples back to Earth in late 2020.

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How did the outer solar system form?

A new study led by the Massachusetts Institute of Technology (MIT) in Cambridge shows that a vast magnetic field extended throughout our solar system as it was forming. The field was weaker in the outer region, but still strong enough to help form asteroids and even the gas giant and ice giant planets. The researchers said on November 6, 2024, that they found clues to this giant, ancient magnetic field in tiny grains from asteroid Ryugu. The Japanese Hayabusa2 mission brought the samples back to Earth in 2020. Ryugu is believed to have formed on the outskirts of the early solar system before migrating in toward the asteroid belt, eventually settling into an orbit between Earth and Mars. So it’s a messenger from that part of space, providing clues to ancient forces shaping our solar system.

The outer magnetic field would have pulled gas and dust inward to form asteroids and perhaps even help form the giant planets Jupiter, Saturn, Uranus and Neptune. Benjamin Weiss at MIT said:

We’re showing that everywhere we look now, there was some sort of magnetic field that was responsible for bringing mass to where the sun and planets were forming. That now applies to the outer solar system planets.

The researchers published their peer-reviewed results in the journal AGU Advances on November 6, 2024.

Analyzing grain samples from asteroid Ryugu

This outer magnetic field would have been very weak. As a comparison, the vast field would have been about 15 microtesla, while our own little Earth’s magnetic field today is around 50 microtesla.

The researchers studied asteroid grains from asteroid Ryugu for evidence of this ancient, weak magnetic field in the outer solar system. The research team, led by MIT, acquired several individual grains for study. Each one was tiny, only about 1 millimeter (0.04 inches) in size. Using a magnetometer, they measured each particle’s magnetization in terms of strength and direction. Then, they demagnetized each grain by using an alternating magnetic field. The process was kind of like rewinding a tape recorder. Lead author Elias Mansbach, formerly at MIT and now the University of Cambridge in the U.K., explained:

Like a tape recorder, we are slowly rewinding the sample’s magnetic record. We then look for consistent trends that tell us if it formed in a magnetic field.

Weak magnetic field in outer solar system

The analysis showed no clear signs of a preserved magnetic field. So did that mean there was no magnetic field present in the early outer solar system? Not necessarily. The magnetic field could have been very weak. The results placed an upper limit of 15 microtesla in intensity.

So, was there a magnetic field or not?

Roughly diamond-shaped gray rocky body in space, with  many boulders and rocks on its surface.
Asteroid Ryugu, as seen by the Hayabusa2 spacecraft on July 12, 2018. Image via JAXA Hayabusa2/ Wikimedia Commons (CC BY 4.0).

Further clues from meteorites

In addition, the researchers examined data from meteorites that had been studied previously. In particular, they looked at meteorites thought to have formed in the outer solar system, and known as ungrouped carbonaceous chondrites. Previously, scientists thought that they were not old enough to have formed before the solar nebula completely dissipated. But Mansbach and his team wanted to take another look. They found they were indeed older than previously estimated. So they did form in the outer reaches of the solar nebula, which became the outer solar system. And they were magnetic. Mansbach said:

We reanalyzed the ages of these samples and found they are closer to the start of the solar system than previously thought. We think these samples formed in this distal, outer region. And one of these samples does actually have a positive field detection of about 5 microtesla, which is consistent with an upper limit of 15 microtesla.

In other words, those meteorite samples fit within the upper magnetic field limit of the Ryugu samples. This implies that there was a weak magnetic field in the early formation of the outer solar system. And although weaker than the magnetic field closer in to the sun, it could still pull in enough gas and dust to form asteroids and even the giant planets. Weiss added:

When you’re farther from the sun, a weak magnetic field goes a long way. It was predicted that it doesn’t need to be that strong out there, and that’s what we’re seeing.

Asteroid Bennu

Now, the research team want to examine samples from the asteroid Bennu, which resembles Ryugu. NASA’s OSIRIS-REx spacecraft brought those samples back to Earth in September 2023. Mansbach said:

Bennu looks a lot like Ryugu, and we’re eagerly awaiting first results from those samples.

Bottom line: A new study of grain samples from asteroid Ryugu shows that an ancient magnetic field helped form asteroids and planets the early outer solar system.

Source: Evidence for Magnetically-Driven Accretion in the Distal Solar System

Via MIT

Read more: Asteroid Ryugu harbors life’s building blocks

Read more: Japan’s Hayabusa2 lands on asteroid Ryugu

Posted 
November 12, 2024
 in 
Space

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