This article has been reviewed according to Science X's editorial process and policies . Editors have highlighted the following attributes while ensuring the content's credibility:
In this study, NRM measurements suggest that the observed characteristics of Ryugu particles is a chemical remanent magnetization, likely acquired during growth of framboidal magnetite that occurred due to water-driven alteration on Ryugu's parent body. Credit: Associate Professor Masahiko Sato from Tokyo University of Science, Japan. Image source link: agupubs.onlinelibrary.wiley.com/doi/10.1029/2025JE009265
To uncover the history of our solar system, it is necessary to study the dynamic evolution of the ancient solar nebula materials. These materials interacted and coevolved with the weak but widespread magnetic field of the solar nebula, which was generated by the weakly ionized nebular gas in the protoplanetary disk. During the formation or alteration, the magnetization of these materials can become locked in for billions of years, a phenomenon known as natural remanent magnetization (NRM). NRM measurements of primordial astromaterials can therefore provide critical information on the spatiotemporal evolution of the early solar system.
Understanding the spatiotemporal evolution of magnetic fields within the protoplanetary disk provides key constraints on the disk's mass distribution. This would aid in reconstruction of how material was transported within the disk and how the solar system was formed.
Ryugu as a primordial time capsule
Ryugu is a small, primitive, carbon-rich, near-Earth asteroid that is thought to be a rubble-pile remnant of a parent body that experienced catastrophic disruption events early in solar system history. As such, it preserves the primordial astromaterials that may retain NRM acquired shortly after the formation of the solar system.
Samples from Ryugu, returned to Earth by Japan's Hayabusa2 spacecraft in 2020, offer a unique opportunity to investigate the magnetic and dynamical evolution of early solar system materials. These materials have minimal magnetic field contamination from Earth due to careful handling and curation, which can be traced and accounted for.
Expanding on previous magnetic studies
While stepwise alternating field demagnetization (AFD) measurements of NRM on seven Ryugu particles have been conducted in previous studies, there is no consensus regarding the interpretation of the results due to the limited number of samples.
To address this gap, a research team led by Associate Professor Masahiko Sato from the Department of Physics at Tokyo University of Science, Japan, conducted stepwise AFD measurements on 28 Ryugu particles.
"Our highly sensitive magnetic measurements on microsamples collected from the asteroid Ryugu provided sufficient magnetic data to finally clarify the differing interpretations obtained by previous research groups, thereby offering important clues for understanding the evolution of the early solar system," explains Dr. Sato.
Their findings are published in the Journal of Geophysical Research: Planets.
How the team measured magnetization
The team carried out systematic paleomagnetic measurements with stepwise AFD on 28 submillimeter-sized Ryugu particles. The measurements were conducted utilizing the superconducting quantum interference device (SQUID) magnetometer at the University of Tokyo, Japan.
The results showed that 23 of 28 Ryugu samples exhibited stable NRM components. Among these, eight particles demonstrated two stable components. In addition, one particle exhibited spatially inhomogeneous NRM directions.
Clues to when magnetization was acquired
Notably, the spatially inhomogeneous NRM directions suggest that magnetization was acquired before final solidification of the particles, indicating that magnetization events occurring late, such as during spacecraft handling after sampling or on Earth, cannot explain the observed NRM characteristics.
Furthermore, the results strongly suggest that these NRM characteristics are a chemical remanent magnetization, likely acquired during the growth of tiny magnetic minerals known as framboidal magnetite that occurred due to water-driven alteration on Ryugu's parent body.
"This means that these particles preserve a record of the magnetic field of the very early solar system, potentially within ~3–7 million years after its formation," notes Dr. Sato.
Together, these findings shed new light on the magnetic characteristics of Ryugu particles, and consequently, on the evolutionary history of our solar system. This will help researchers constrain the physical conditions under which planets formed and material evolved, including those that ultimately led to the formation of Earth.
Publication details Masahiko Sato et al, Characteristics of Natural Remanence Records in Fine‐Grained Particles Returned From Asteroid Ryugu, Journal of Geophysical Research: Planets (2026). DOI: 10.1029/2025je009265 Journal information: Journal of Geophysical Research
— Source: Phys.org (https://phys.org/news/2026-03-asteroid-ryugu-samples-insights-early.html)
