A 4.6 billion-year-old “recorder” was hidden in asteroid dust: what it said changes what we knew

We think of memory as something linked to memories that fade or transform over time. But there is another form of memory that is much more precise and stubborn, one that does not depend on people or technology and still preserves information with extraordinary fidelity. Some rocks are capable of recording the magnetic environment in which they were formed. That is what happens with the dust of a very particular asteroid: small particles that have preserved a magnetic signal for billions of years that today allows us to reconstruct what the solar system was like in its early stages.

That “record” is not a metaphor. It comes from particles collected on the asteroid Ryugu and brought to Earth in 2020 by Japan’s Hayabusa2 mission. As Eurekalert points outa team led by Masahiko Sato has analyzed their magnetic behavior and has found signals that suggest that these particles retained information from the environment in which they were formed. This opens the door to reconstructing what the magnetic fields present in the protoplanetary diskthat is, the “nursery” where the planets were formed.

A trace that cannot be erased. The key is how some minerals react to the magnetic field when they form. Its internal structures, formed by small magnetic domains, are oriented following that field and remain “locked” when the material solidifies. That process leaves a lasting mark that scientists can measure today with highly sensitive instruments. This phenomenon, known as natural remanent magnetization, turns these particles into physical witnesses of the past.

The challenge. The first analyzes of these samples offered very different conclusions: some studies suggested that they preserved a stable magnetic signal from the early solar system, while others argued that they had formed in a region with practically no magnetic field. There were also those who suggested that the signals detected could be due to contamination during analysis on Earth. Part of the problem was based on these works, which were based on a very limited number of particles, just seven, which made it difficult to obtain solid conclusions.

New samples. To resolve these discrepancies, The team significantly expanded the number of particles analyzedgoing from seven to 28, which allowed us to work with a much more solid statistical base. After applying demagnetization techniques to eliminate possible modern signals, the results showed a clearer pattern: 23 of the 28 particles retained a stable magnetic signal. Of these particles, eight showed two stable components and one presented spatially inhomogeneous magnetization directions, something difficult to explain if the signal had been introduced later on Earth.

Why is it important. The detected signals suggest that these materials originated in an early phase of the solar system, approximately between 3 and 7 million years after its formation. They also point to water alteration processes in the asteroid’s parent body. So we can say with great confidence that Ryugu is not just a pile of rocks: it is a valuable archive of the early solar system that has allowed us to better understand the magnetic environment of those times.

Images | JAXA

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A 4.6 billion-year-old “recorder” was hidden in asteroid dust: what it said changes what we knew

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Xataka

by
Javier Marquez

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