POSTDOCTORAL work
A 4,565 million years old record of the solar nebula field
Magnetic fields in protoplanetary disks are thought to play a prominent role in the formation of planetary bodies. Acting upon angular momentum transport, they can influence the motion of solids and accretion onto the star. By searching for the record of the solar nebula field preserved in meteorites, we aim at characterizing the strength of a disk field with a spatial and temporal resolution far superior to observations of extrasolar disks. The meteorite Erg Chech 002 formed from the volcanic crust of its parent body. We show that this meteorite carries an ancient magnetization, acquired only 2 million years after the formation of the first solids in the solar nebula. This magnetization reflects the intensity of the field in the disk at that epoch; it is one of the two oldest records to date of the solar nebula field. Magnetic fields are increasingly regarded as essential to the early phases of planetary accretion. Such paleomagnetic data are crucial in guiding the development of dynamical models to advance our understanding of planetary formation. |
The meteorite Erg Chech 002
(credit: Luc Labenne, Labenne Meteorites) |
The sample C0005 of asteroid Ryugu
(credit: JAXA) |
Paleomagnetic investigation of samples returned from asteroid Ryugu
The JAXA Hayabusa 2 mission returned 5.4 g of material from the C-type asteroid Ryugu. In this study, we investigated the possibility that magnetite and pyrrhotite, which are aqueous alteration products found in Ryugu samples, acquired a remanent magnetization reflecting the nebula field intensity. However, we found that none of our samples exhibit a stable natural remanent magnetization. This indicates that the aqueous alteration of Ryugu's parent body took place either in a field of a few µT, or in a very weak to null field. In the former scenario, the solar nebula field is the most likely magnetizing field, implying that aqueous alteration occurred before its dissipation, i.e., before ∼5 Myr after CAI formation. In the latter scenario, aqueous alteration must have occurred either after the dissipation of the nebula, or at an earlier epoch and a large heliocentric distance (> 5 au). The similarities between Ryugu samples and CI chondrites favor this second hypothesis. |
Estimating ancient field intensities from chemical remanent magnetizations in meteorites
Many meteorites experienced aqueous alteration on their parent body. During this process, magnetite usually forms, and will acquire a chemical remanent magnetization (CRM) if growing in the presence of a magnetic field. Therefore, magnetite-bearing meteorites are a potential source of invaluable data regarding the intensity of the solar nebula magnetic field and its effects on planetary accretion. The major limitation so far encountered is the lack of a well-defined empirical law relating the measured CRM to the intensity of the magnetizing field. In this work, we determine such an empirical law through a series of CRM acquisition experiments. This allows us to obtain more precise field intensity estimates from magnetite-bearing meteorite carrying a CRM. |
Comparing our empirical law with the one used so far in paleomagnetic studies
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DOCTORAL WORK
Magnetic evidence for planetesimal partial differentiation
Planetesimals may have experienced various degrees of melting, and some may have been only partially differentiated (i.e., with a metallic core, melted silicate mantle and unmelted crust). This would imply that some chondrites and achondrites could share common parent bodies, and that accretion was likely protracted to allow for the survival of chondritic crusts. The IIE iron meteorites are excellent candidate to investigate partial differentiation, as they contain both melted and unmelted silicate inclusions of common origin. Using a synchrotron-based technique, we measured the magnetization of two IIE irons. We found they both recorded a magnetic field most compatible with a dynamo-generated field powered by crystallization of their parent body’s core. This makes IIE irons the first meteorite group found to have preserved the record of all three layers of a partially-differentiated planetesimal: chondritic crust, achondritic mantle, metallic core. |
The IIE iron Techado
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The IIE iron Miles
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Timing planetesimal core crystallization and dynamo activity
The existence of numerous iron meteorite groups indicates that some planetesimals underwent melting that led to metal-silicate segregation, sometimes producing metallic cores. Meteorite paleomagnetic records suggest that crystallization of these cores led to the generation of dynamo magnetic fields. Here we propose the most extended time-resolved paleomagnetic record for the partially differentiated IIE iron meteorite parent body constrained by 40Ar/39Ar chronometry. We find that the core of the IIE parent body generated a dynamo, likely powered by core crystallization, starting before ~80 million years (Ma) after solar system formation and lasting at least 80 Ma. Such extended core crystallization suggests that the core composed a substantial fraction of the body, indicating efficient core formation within some partially differentiated planetesimals. |
Formation of the cloudy zone in iron-rich meteorites
The cloudy zone, a nanoscale intergrowth of Ni-rich “islands” and Ni-poor matrix, forms below 360°C in slow-cooled iron, stony-iron and iron-rich chondrite meteorites. The size of the islands inversely correlates with the meteorite’s cooling rate. The islands can also preserve the record of a magnetic field they experienced during growth. To take full advantage of these recording capacities, I created a numerical model of cloudy zone formation in the cooling environment of a meteorite’s parent body. I use this model to constrain magnetic field intensities and low-temperature cooling rates experienced by the meteorites. |
SEM image of the cloudy zone
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A big iron meteorite at the Smithsonian
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Size dependence of the magnetization in iron meteorite samples
The spacecraft of the NASA mission Psyche will establish whether the largest known metallic asteroid (16) Psyche is the core of an ancient planetesimal by searching for evidence of a remanent magnetic field imparted by an extinct dynamo. One way to experimentally constrain the expected magnetic intensity at Psyche is to study the magnetization of potential analogs: iron meteorites. We built a magnetometer array to measure the magnetization of meter-size meteorites at the Smithsonian Institution and I am now completing the study by measuring the magnetizations of cm- and mm-size samples. |
Impact craters on metallic targets
Estimate the relative surface ages and identify resurfacing events of (16) Psyche can be done by counting impact craters imaged by the spacecraft. However, limited attention has been drawn to impacts in metal-rich objects for planetary applications. More laboratory experiments and numerical simulations calibrated against them are needed. I conducted a suite of numerical simulations using a SPH numerical code aiming at reproducing high-velocity impact experiments conducted on steel targets. I investigated the effect of crucial parameters such as the equation of state or the initial flaw distribution in the material. |
SPH impact simulation
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Before my PhD
N-body simulation of a lander in a regolith bed
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Interaction between a lander and an asteroid regolith surface
Several landers have already touched asteroid surfaces. The behavior of the lander after first touchdown is a hard but critical variable to predict. This is because 1) the quality of the following measurements depends on the quality of the landing, and 2) the trajectory of the lander provides invaluable insights on the surface properties of the visited body. In this work, we explored numerically the influence of the lander and regolith mechanical properties, as well as regolith layer thickness on the outcome of a landing in microgravity. We also investigated how a postimpact visualization of the contact site(s) may help to infer non-observable properties of the regolith layer. |
Motion-driven grain size sorting in asteroids regolith
Understanding the connection between surface properties and internal structure on asteroids is essential given that most spacecraft instruments can only characterize the surface. However, because of their microgravity environment, small perturbations may be enough to disturb asteroid surfaces in complex ways. In this work, we used N-body simulations to compare how large boulders in a bed of small grains can reach the surface after repeated shakings. Such mechanism of grain segregation could explain the presence of large boulders at the surface of small bodies such as Itokawa, Ryugu, Bennu. |
The asteroid Itokawa and its boulders
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The asteroid (1) Ceres
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Influence of (1) Ceres on the dynamical evolution of asteroid families
Orbital resonances play a significant role in the long-term dynamical stability of planetary systems. In particular, secular resonances occur when the precession of an asteroid’s angular orbital elements is synchronized with that of a disturber, typically a planet. We considered for the first time the influence of the largest asteroid of the main belt, (1) Ceres, on the dynamical evolution of nearby asteroid families. This work highlights the importance of considering not only planets but also large neighboring asteroids in the study of the dynamics of asteroid families. |