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How asteroid collisions can create magnetic fields

Yale researchers have made significant progress in unraveling a longstanding puzzle related to certain metallic meteorites displaying traces of a magnetic field. This discovery could potentially shed light on the formation of magnetic dynamos at the cores of planets.

Understanding planetary magnetism is crucial for comprehending the internal structure and of celestial bodies. Notably, Earth, Mercury, Ganymede, and Io generate detectable magnetic fields. Additionally, evidence of ancient magnetism has been found on Mars and Earth's moon.

Among the curious findings are certain meteorites, small space rocks that have fallen to Earth, showing hints of magnetism. Scientists have observed that some iron meteorites retain remnants of an internally-generated magnetic field, which appears to be unexpected. Iron meteorites are generally considered to represent the metallic cores of asteroids, yet these cores are not expected to possess the highly specific internal characteristics required to generate and record magnetism simultaneously.

In an exciting new study, Yale scientists Zhongtian Zhang and David Bercovici propose a potential explanation for this . They suggest that, under specific conditions, collisions between asteroids could lead to the formation of metal asteroids capable of generating a magnetic field and recording the magnetism within their own materials. Consequently, small fragments from these asteroids, carrying traces of magnetism, could fall to Earth as meteorites.

The study, published in the journal Proceedings of the National Academy of Sciences, started with Zhang's awareness of the puzzle and his prior discussions with Dave, a professor at Yale's Department of Earth & Planetary Sciences. As Zhang researched “rubble-pile” asteroids, formed when gravitational forces cause fragments of asteroid collisions to re-form in new combinations, he became inspired to explore whether this phenomenon could be linked to the generation of a magnetic field.

Based on their modeling, the researchers proposed that following an asteroid collision, new iron-heavy asteroids could form with a cold, rubble-pile inner core surrounded by a warmer liquid outer layer. When the colder core draws heat from the outer layer and releases lighter elements like sulphur, it initiates convection, leading to the creation of a magnetic field.

According to their model, such a dynamo effect could generate a magnetic field lasting several million years, a sufficient duration for its presence to be detected in iron meteorites by scientists billions of years later.

David Bercovici praised Zhang's creative solution, particularly the concept of a rubble-pile core resembling “dropping ice cubes into a molten metal,” where an optimal size would cool in space and sink quickly into the melted metal to form an inner core akin to Earth's, at least for a limited period.

This research represents a remarkable step forward in unraveling the mysteries of planetary magnetism and the fascinating origins of certain meteorites.

Source: Yale University

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