Magnetic Properties of Iron Meteorites and Their Parent Bodies
This thesis investigates fundamental properties of the first planetary bodies of our solar system. Similar to Earth, some of these “planetesimals” underwent differentiation into a metallic core and a silicate mantle, and powered magnetic fields by the motion of their liquid cores via dynamo effect....
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Massachusetts Institute of Technology
2022
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| Online Access: | https://hdl.handle.net/1721.1/140026 https://orcid.org/0000-0002-4257-5318 |
| Summary: | This thesis investigates fundamental properties of the first planetary bodies of our solar system. Similar to Earth, some of these “planetesimals” underwent differentiation into a metallic core and a silicate mantle, and powered magnetic fields by the motion of their liquid cores via dynamo effect. Although most planetesimals no longer exist, records of their magnetic fields are preserved in meteorites and asteroids. These records offer the opportunity to better characterize the intrinsic properties of this primordial population. Here I present a series of paleomagnetic studies conducted on iron meteorites, potential carriers of such magnetic signatures.
First, I focus on the IIE iron meteorites. This peculiar meteorite group is thought to have formed on a planetesimal that underwent only partial differentiation, but the processes leading to the formation and evolution of such object remain poorly constrained. To better characterize these processes, I conduct synchrotron-based micromagnetic measurements on the IIE meteorites. One major outcome of this project is a time-resolved record of the dynamo activity of the IIE parent body. This record demonstrates that some partially-differentiated planetesimals formed sizable metallic cores and remained magnetically active for hundreds of millions of years. In addition, I develop a model of formation of the magnetic microstructures in iron-rich meteorites, which advances the field along two axes: it quantifies important sources of uncertainty in paleomagnetic data and serves as indicator of the cooling rate of these meteorites.
Second, I focus on the following observation: in contrast with the multiple evidence for magnetized meteorites, no magnetized asteroid has so far been identified. To explain this apparent discrepancy, it has been hypothesized that because magnetization decreases with sample size, it would be inherently undetectable at asteroid scale. To test this hypothesis, I present a new magnetometer array accommodating meter-size samples, and combine measurements of iron meteorites at multiple size scales. This work shows that measured magnetization need not be reduced to zero as size increases but instead may asymptote at a non-zero value. Consequently, size does not prevent asteroid magnetization to be detected, although multiple other factors may hinder the detection. |
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