8 research outputs found
Detrital remanent magnetization in the solar nebula
No full textWe introduce the theoretical basis of a new form of remanent magnetization that likely formed on primitive bodies in the solar system. Accretional detrital remanent magnetization (ADRM) operates via “compass needle”-type alignment of ferromagnetic solids with locally uniform background fields in the solar nebula. Accretion of coherently aligned magnetic particles should have formed aggregates up to centimeters in size with significant net magnetic moment. We quantify several processes that constrain the likelihood of ADRM formation, finding that rotational gas damping and background field intensities expected for the solar nebula are sufficient to mutually align magnetic particles with diameters between ∼30 μm and several cm. The lower bound is dictated by Brownian motion or radiative torque while the upper bound is set by aerodynamic torque on non-spherical particles. Processes important for interstellar dust dynamics such as Larmor-type precession and Purcell torque are less significant in the solar nebula. ADRM can be potentially observed as zones of coherent magnetization in primitive chondrites and may be detected by spacecraft magnetic field observations on the surfaces of small bodies. Observational identification and characterization of ADRM would constrain the strength and geometry of magnetic fields in the early solar system, the accretion process of sub-meter sized objects, the formation regions of chondrite parent bodies, and the alteration history of chondritic components.United States. National Aeronautics and Space Administration. Origins Progra
ARCSECOND RESOLUTION MAPPING OF SULFUR DIOXIDE EMISSION IN THE CIRCUMSTELLAR ENVELOPE OF VY CANIS MAJORIS
No full textWe report Submillimeter Array observations of SO[subscript 2] emission in the circumstellar envelope (CSE) of the red supergiant VY Canis Majoris, with an angular resolution of ≈1''. SO[subscript 2] emission appears in three distinct outflow regions surrounding the central continuum peak emission that is spatially unresolved. No bipolar structure is noted in the sources. A fourth source of SO[subscript 2] is identified as a spherical wind centered at the systemic velocity. We estimate the SO[subscript 2] column density and rotational temperature assuming local thermal equilibrium (LTE) as well as perform non-LTE radiative transfer analysis using RADEX. Column densities of SO[subscript 2] are found to be ~10[superscript 16] cm[superscript –2] in the outflows and in the spherical wind. Comparison with existing maps of the two parent species OH and SO shows the SO2 distribution to be consistent with that of OH. The abundance ratio [fSO[subscript 2] over fSO] is greater than unity for all radii larger than 3 × 10[superscript 16] cm. SO[subscript 2] is distributed in fragmented clumps compared to SO, PN, and SiS molecules. These observations lend support to specific models of circumstellar chemistry that predict [fSO[subscript 2] over fSO] > 1 and may suggest the role of localized effects such as shocks in the production of SO2 in the CSE
Efficient early global relaxation of asteroid Vesta
No full textThe asteroid Vesta is a differentiated planetesimal from the accretion phase of Solar System formation. Although its present-day shape is dominated by a non-hydrostatic fossil equatorial bulge and two large, mostly unrelaxed impact basins, Vesta may have been able to approach hydrostatic equilibrium during a brief early period of intense interior heating. We use a finite element viscoplastic flow model coupled to a 1D conductive cooling model to calculate the expected rate of relaxation throughout Vesta’s early history. We find that, given sufficient non-hydrostaticity, the early elastic lithosphere of Vesta experienced extensive brittle failure due to self-gravity, thereby allowing relaxation to a more hydrostatic figure. Soon after its accretion, Vesta reached a closely hydrostatic figure with 40–200 My after formation, depending on the assumed depth of megaregolith. The Veneneia and Rheasilvia giant impacts, which generated most non-hydrostatic topography, must have therefore occurred >40–200 My after formation. Based on crater retention ages, topography, and relation to known impact generated features, we identify a large region in the northern hemisphere that likely represents relic hydrostatic terrain from early Vesta. The long-wavelength figure of this terrain suggests that, before the two late giant impacts, Vesta had a rotation period of 5.02 h (6.3% faster than present) while its spin axis was offset by 3.0 ° from that of the present. The evolution of Vesta’s figure shows that the hydrostaticity of small bodies depends strongly on its age and specific impact history and that a single body may embody both hydrostatic and non-hydrostatic terrains and epochs.National Science Foundation (U.S.). Graduate Research Fellowship Progra
Magnetic fields in the early solar system
No full textThesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2015.Cataloged from PDF version of thesis.Includes bibliographical references (pages 251-283).The first magnetic fields in the solar system were embedded in the ionized gas of the protoplanetary disk itself. Soon after, newly formed protoplanets may have harbored magnetic core dynamos. Paleomagnetic analysis of ancient samples permits direct constraints on these early solar system magnetic fields. Here I present paleomagnetic studies of several classes of meteorites. Experiments on inclusions of chondritic meteorites have led to some of the first constraints on the intensities of protoplanetary disk magnetic fields. Meanwhile, measurements of eucrites, a class of achondrites believed to originate from the asteroid Vesta, suggest that Vesta once hosted a magnetic core dynamo. New techniques developed during the course of these measurements permit ongoing and future investigations of the remanent magnetizations of new meteorites and terrestrial rocks. In support of the paleomagnetic results, I present analytical and numerical modeling of magnetic dust grain dynamics in the solar nebula and of the interior dynamics of differentiated asteroids capable of hosting magnetic dynamos.by Roger R. Fu.Ph. D
Micrometer-scale magnetic imaging of geological samples using a quantum diamond microscope
No full textRemanent magnetization in geological samples may record the past intensity and direction of planetary magnetic fields. Traditionally, this magnetization is analyzed through measurements of the net magnetic moment of bulk millimeter to centimeter sized samples. However, geological samples are often mineralogically and texturally heterogeneous at submillimeter scales, with only a fraction of the ferromagnetic grains carrying the remanent magnetization of interest. Therefore, characterizing this magnetization in such cases requires a technique capable of imaging magnetic fields at fine spatial scales and with high sensitivity. To address this challenge, we developed a new instrument, based on nitrogen-vacancy centers in diamond, which enables direct imaging of magnetic fields due to both remanent and induced magnetization, as well as optical imaging, of room-temperature geological samples with spatial resolution approaching the optical diffraction limit. We describe the operating principles of this device, which we call the quantum diamond microscope (QDM), and report its optimized image-area-normalized magnetic field sensitivity (20 µT⋅µm/Hz1/2), spatial resolution (5 µm), and field of view (4 mm), as well as trade-offs between these parameters. We also perform an absolute magnetic field calibration for the device in different modes of operation, including three-axis (vector) and single-axis (projective) magnetic field imaging. Finally, we use the QDM to obtain magnetic images of several terrestrial and meteoritic rock samples, demonstrating its ability to resolve spatially distinct populations of ferromagnetic carriers.United States. National Aeronautics and Space Administration. Planetary Major Equipment Program (NNX15AH72G)United States. National Aeronautics and Space Administration. Emerging Worlds ProgramNational Science Foundation (U.S.). Integrated Support Promoting Interdisciplinary Research and Education (INSPIRE) Program (grant EAR 1647504)National Science Foundation (U.S.). Electronics, Photonics and Magnetic Devices Program (grant 1408075)United States. Defense Advanced Research Projects Agency. Quantum Assisted Sensing And Readout Program (contract HR0011‐11‐C‐0073)Thomas F. Peterson Jr. (generous gift
Paleomagnetism. Solar nebula magnetic fields recorded in the Semarkona meteorite.
No full textMagnetic fields are proposed to have played a critical role in some of the most enigmatic processes of planetary formation by mediating the rapid accretion of disk material onto the central star and the formation of the first solids. However, there have been no experimental constraints on the intensity of these fields. Here we show that dusty olivine-bearing chondrules from the Semarkona meteorite were magnetized in a nebular field of 54 ± 21 microteslas. This intensity supports chondrule formation by nebular shocks or planetesimal collisions rather than by electric currents, the x-wind, or other mechanisms near the Sun. This implies that background magnetic fields in the terrestrial planet-forming region were likely 5 to 54 microteslas, which is sufficient to account for measured rates of mass and angular momentum transport in protoplanetary disks
Raw data for: Magnetic response and hardness enhancement by spontaneous directional coarsening of Fe2AlB2 in quasicrystal-rich matrix
No full textPreliminary part of the research was funded within the National Science Centre, Poland (NCN) research task No. 2018/02/X/ST5/02997 (Miniatura, based in Wroclaw University of Science and Technology, Poland - synthesis and thermal treatment, initial characterization).Most significant part of the data collected (magnetic, microstructural and atomic structure) was acquired within the National Science Centre, Poland (NCN) research grant No. 2020/36/C/ST5/00007 (Sonatina, based in the University of Wroclaw, Faculty of Chemistry, Poland). Hardness tests were performed from the PI's private funds. EBSD analyses were carried out at the Caltech GPS Division Analytical Facility, which is supported, in part, by NSF Grants EAR-0318518 and DMR-0080065.NV ODMR analyses were performed at the Department of Earth and Planetary Sciences, Harvard University, USA. The data contained within the dataset are only a part of data obtained within the mentioned projects that is associatd with one manuscript, that will be associated with the data after its publication.Miniatura project was aimed at determination, which alloy compositions can be doped with Si/B without causing the formation of other crystalline phases than the desired icosahedral phase and correlating this data with temperature stability, as well as determining changes in the quasi-lattice constant. This aimed to enable a more precise selection of alloy compositions in the subsequent Sonatina project. Sonatina project was aimed at development of the novel multi-phase aluminum-based alloy compositions that contain quasicrystalline phases and exhibit long-range magnetic order at near-room temperature. The task includes determination of structure, thermal stability and fundamental magnetic properties of the studied materials. Another aim was the unequivocal assignment of the investigated magnetic properties to the certain quasicrystalline microstructural phases of the chosen alloys.Person responsible for dataset preparation: Piotr Józef Bardziński (piotr.bardzinski@pwr.edu.pl, Department of Semiconductor Materials Engineering, WPPT, Wrocław University of Science and Technology, Wybrzeże Stanisława Wyspiańskiego 27, 50-370 Wrocław, Poland; former affiliation: Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14 St., 50-383 Wrocław, Poland where the project Sonatina was based)Co-investigators (another tasks of the project Sonatina, not associated with this dataset, involved more co-investigators): Piotr J. Bardziński (PI, currently employed at WUST Poland) and Marek Weselski (University of Wroclaw, Poland), Paul D. Asimow and Jinping Hu (Caltech, USA), Roger Rennan Fu (Harward, USA)Piotr Józef Bardzinski, Marek Weselski, Paul D. Asimow, Jinping Hu, Roger Rennan Fu. Magnetic response and hardness enhancement by spontaneous directional coarsening of Fe2AlB2 in quasicrystal-rich matrix. (related publication is submitted to journal).Please consult the Readme.txt file for additional information.</p
The missing large impact craters on Ceres
No full textAsteroids provide fundamental clues to the formation and evolution of planetesimals. Collisional models based on the depletion of the primordial main belt of asteroids predict 10–15 craters >400 km should have formed on Ceres, the largest object between Mars and Jupiter, over the last 4.55 Gyr. Likewise, an extrapolation from the asteroid Vesta would require at least 6–7 such basins. However, Ceres’ surface appears devoid of impact craters >∼280 km. Here, we show a significant depletion of cerean craters down to 100–150 km in diameter. The overall scarcity of recognizable large craters is incompatible with collisional models, even in the case of a late implantation of Ceres in the main belt, a possibility raised by the presence of ammoniated phyllosilicates. Our results indicate that a significant population of large craters has been obliterated, implying that long-wavelength topography viscously relaxed or that Ceres experienced protracted widespread resurfacing
