Scientists studying tiny samples from the asteroid Ryugu have uncovered new clues about the magnetic environment that existed when the solar system first formed.
The findings help researchers better understand how the swirling disk of gas and dust around the young sun eventually produced planets, moons, and asteroids.
More than 4.5 billion years ago, the solar system formed from a giant cloud of gas and dust called the solar nebula.
This material gradually flattened into a rotating disk known as a protoplanetary disk.
Within this disk, particles collided and stuck together, slowly forming larger bodies such as asteroids and planets. During this time, the disk was threaded with a weak but widespread magnetic field created by the ionized gas within it.
As dust and rock particles formed and changed over time, some of them recorded this magnetic environment.
Their minerals could lock in a signal from the magnetic field, preserving it for billions of years. This phenomenon is known as natural remanent magnetization.
By measuring this magnetic signal in ancient space materials, scientists can learn about the magnetic conditions that existed when those materials formed.
Asteroid Ryugu offers a rare opportunity to study such ancient material. The small, carbon-rich asteroid is thought to be the remains of a much larger parent body that was shattered long ago in the early solar system.
Because of this violent history, Ryugu is considered a “rubble pile” asteroid made from fragments of its original body. Despite this, the asteroid still preserves extremely primitive materials that formed near the beginning of the solar system.
In 2020, Japan’s Hayabusa2 spacecraft successfully collected samples from Ryugu and returned them to Earth. These samples are especially valuable because they were handled very carefully to prevent contamination by Earth’s magnetic field.
A research team led by Masahiko Sato from the Tokyo University of Science analyzed the magnetism of these particles to better understand their history.
The study was published in Journal of Geophysical Research: Planets.
Previous studies had examined only a small number of Ryugu particles, which made it difficult for scientists to agree on how to interpret the results. To address this problem, Sato’s team expanded the analysis by measuring 28 tiny particles taken from the asteroid.
The researchers used an extremely sensitive instrument called a SQUID magnetometer, located at the University of Tokyo. This device can detect incredibly weak magnetic signals preserved inside microscopic samples.
The measurements showed that most of the particles still contained stable magnetic signals from the past. Some particles even recorded multiple magnetic components, suggesting they experienced different stages of magnetic activity during their history.
The team also found evidence that the magnetization likely formed during chemical reactions involving water on Ryugu’s original parent body. These reactions produced tiny magnetic minerals known as framboidal magnetite, which captured the surrounding magnetic field as they formed.
This discovery suggests that the particles recorded the solar system’s magnetic environment very early in its history, possibly within about three to seven million years after the solar system first formed.
By studying these ancient magnetic fingerprints, scientists can gain a better picture of how material moved through the early solar system and how the conditions in the protoplanetary disk shaped the formation of planets—including Earth itself.
