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Before NASA’s Dawn mission, the dwarf planet Ceres was widely believed to contain a substantial ice-rich layer below its rocky surface. The existence of such a layer has significant implications for Ceres’s formation, evolution, and astrobiological potential. Ceres is warmer than icy worlds in the outer Solar System and, if its shallow subsurface is ice-rich, large impact craters are expected to be erased by viscous flow on short geologic timescales. Here we use digital terrain models derived from Dawn Framing Camera images to show that most of Ceres’s largest craters are several kilometres deep, and are therefore inconsistent with the existence of an ice-rich subsurface. We further show from numerical simulations that the absence of viscous relaxation over billion-year timescales implies a subsurface viscosity that is at least one thousand times greater than that of pure water ice. We conclude that Ceres’s shallow subsurface is no more than 30% to 40% ice by volume, with a mixture of rock, salts and/or clathrates accounting for the other 60% to 70%. However, several anomalously shallow craters are consistent with limited viscous relaxation and may indicate spatial variations in subsurface ice content. The dwarf planet Ceres is thought to have an ice-rich layer in its shallow subsurface. The morphologies of craters, however, suggest little relaxation by viscous flow has occurred and instead indicate a subsurface that is less than 40% ice.

A key stage in planet formation is the evolution of a gaseous and magnetized solar nebula. However, the lifetime of the nebular magnetic field and nebula are poorly constrained. We present paleomagnetic analyses of volcanic angrites demonstrating that they formed in a near-zero magnetic field (<0.6 microtesla) at 4563.5 ± 0.1 million years ago, ~3.8 million years after solar system formation. This indicates that the solar nebula field, and likely the nebular gas, had dispersed by this time. This sets the time scale for formation of the gas giants and planet migration. Furthermore, it supports formation of chondrules after 4563.5 million years ago by non-nebular processes like planetesimal collisions. The 1core dynamo on the angrite parent body did not initiate until about 4 to 11 million years after solar system formation.

We provide an overview of the experimental techniques, measurement modalities, and diverse applications of the quantum diamond microscope (QDM). The QDM employs a dense layer of fluorescent nitrogen-vacancy (NV) color centers near the surface of a transparent diamond chip on which a sample of interest is placed. NV electronic spins are coherently probed with microwaves and optically initialized and read out to provide spatially resolved maps of local magnetic fields. NV fluorescence is measured simultaneously across the diamond surface, resulting in a wide-field, two-dimensional magnetic field image with adjustable spatial pixel size set by the parameters of the imaging system. NV measurement protocols are tailored for imaging of broadband and narrowband fields, from DC to GHz frequencies. Here we summarize the physical principles common to diverse implementations of the QDM and review example applications of the technology in geoscience, biology, and materials science.

Magnetic 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.

The timing of the formation of the Earth's inner core remains a major mystery in the history of Earth's deep interior, with estimates ranging from >1 billion years to <500 million years. Inner core nucleation is expected to be characterized in the paleomagnetic record by a drop in magnetic field strength prior to inner core nucleation, followed by a sharp increase in strength after nucleation. Paleointensity data from the 1 Ga–500 Ma age range are, however, exceptionally sparse (with fewer than a dozen studies), which largely prevents any definitive conclusions. This study presents new paleointensity results from whole rocks aged 510 ± 5 Ma from the Florida Mountains in southwestern New Mexico. Exceptionally low paleointensity estimates (<2 μT) were measured from three sites in granite and syenite outcrops of the southwestern portion of the Florida Mountains. Detailed rock magnetic and imaging investigations, including Quantum Diamond Microscopy, suggested that the two were unreliable because their remanence was unlikely a pure thermoremanent magnetization. The third site is more trustworthy and gave an estimate of 1.2 ± 0.2 μT (N = 5) corresponding to a virtual dipole moment of 0.4×1022Am2 $0.4\\times {10}^{22}\\,{\\text{Am}}^{2}$, which is of a similar magnitude to the lower bound of estimates from the Ediacaran (635–541 Ma). Such a low estimate at 510 Ma appears inconsistent with recent claims that the field strengthened rapidly following inner core nucleation in the late Ediacaran. Nevertheless, the risk of this single estimate being unrepresentative of the long‐term field should be recognized alongside the urgent need for more paleointensity data spanning the interval 540–440 Ma.

A better understanding of the relative roles of internal climate variability and external contributions, from both natural (solar, volcanic) and anthropogenic greenhouse gas forcing, is important to better project future hydrologic changes. Changes in the evaporative demand play a central role in this context, particularly in tropical areas characterized by high precipitation seasonality, such as the tropical savannah and semi-desertic biomes. Here we present a set of geochemical proxies in speleothems from a well-ventilated cave located in central-eastern Brazil which shows that the evaporative demand is no longer being met by precipitation, leading to a hydrological deficit. A marked change in the hydrologic balance in central-eastern Brazil, caused by a severe warming trend, can be identified, starting in the 1970s. Our findings show that the current aridity has no analog over the last 720 years. A detection and attribution study indicates that this trend is mostly driven by anthropogenic forcing and cannot be explained by natural factors alone. These results reinforce the premise of a severe long-term drought in the subtropics of eastern South America that will likely be further exacerbated in the future given its apparent connection to increased greenhouse gas emissions. Speleothems from the Savanna region in Brazil documents the occurrence of an unprecedented long-term drought driven by anthropogenic forcing. Staring in the 1970´s the current drought is the most severe that has struck the region in the past 700 years.

In well‐buffered modern soils, higher annual rainfall is associated with enhanced soil ferrimagnetic mineral content, especially of ultrafine particles that result in distinctive rock magnetic properties. Hence, paleosol magnetism has been widely used as a paleoprecipitation proxy. Identifying the dominant mechanism(s) of magnetic enhancement in a given sample is critical for reliable inference of paleoprecipitation. Here, we use high‐resolution magnetic field and electron microscopy to identify the grain‐scale setting and formation pathway of magnetic enhancement in two modern soils developed in higher (∼580 mm/y) and lower (∼190 mm/y) precipitation settings from the Qilianshan Range, China. We found that both soils contain 1–30 μm aeolian Fe‐oxide grains with indistinguishable rock magnetic properties, while the higher‐precipitation soil contains an additional population of ultrafine (<150 nm) magnetically distinct magnetite grains. We show that the in situ precipitation of these ultrafine particles, likely during wet‐dry cycling, is the only significant magnetic enhancement mechanism in this soil. These results demonstrate the potential of quantum diamond microscope magnetic microscopy to extract magnetic information from distinct, even intimately mixed, grain populations. This information can be used to evaluate the contribution of distinct enhancement mechanisms to the total magnetization. Plain Language Summary Reconstructing how natural climate variations in the past influenced rainfall patterns is important for understanding how rainfall would respond to our current changing climate. The amount and properties of microscopic, magnetic minerals in soil can change due to variation in soil moisture; therefore, characterizing the magnetic properties of soils can aid in quantifying past rainfall. We use the quantum diamond microscope (QDM), a device that allows micrometer‐scale mapping of magnetic sources in rock and soil samples, to investigate the magnetic properties of two soils formed in low‐ and high‐rainfall environments. We find that, although both soils contain wind‐blown, magnetic dust, only the high‐rainfall soil contains an abundant, highly magnetic population of magnetite grains formed in soil pore spaces during repeated cycles of wetting and drying. These observations demonstrate the dominant pathway by which soil magnetism responds to rainfall and showcase the ability of QDM mapping to reliably identify the mechanism of magnetism modification in soils. Key Points Both high and low precipitation soils contain aeolian grain population with indistinguishable magnetic properties High precipitation soil alone contains anhysteretic remanent magnetization‐susceptible, <150 nm magnetites inferred to be formed from wet‐dry cycling in pore spaces Magnetic field microscopy is able to quantify rock magnetic properties of intimately mixed grain populations and pinpoint their locations

Dusty olivine (olivine containing multiple sub-micrometer inclusions of metallic iron) in chondritic meteorites is considered an ideal carrier of paleomagnetic remanence, capable of maintaining a faithful record of pre-accretionary magnetization acquired during chondrule formation. Here we show how the magnetic architecture of a single dusty olivine grain from the Semarkona LL3.0 ordinary chondrite meteorite can be fully characterized in three dimensions, using a combination of focused ion beam nanotomography (FIB-nT), electron tomography, and finite-element micromagnetic modeling. We present a three-dimensional (3D) volume reconstruction of a dusty olivine grain, obtained by selective milling through a region of interest in a series of sequential 20 nm slices, which are then imaged using scanning electron microscopy. The data provide a quantitative description of the iron particle ensemble, including the distribution of particle sizes, shapes, interparticle spacings and orientations. Iron particles are predominantly oblate ellipsoids with average radii 242 ± 94 × 199 ± 80 × 123 ± 58 nm. Using analytical TEM we observe that the particles nucleate on sub-grain boundaries and are loosely arranged in a series of sheets parallel to (001) of the olivine host. This is in agreement with the orientation data collected using the FIB-nT and highlights how the underlying texture of the dusty olivine is crystallographically constrained by the olivine host. The shortest dimension of the particles is oriented normal to the sheets and their longest dimension is preferentially aligned within the sheets. Individual particle geometries are converted to a finite-element mesh and used to perform micromagnetic simulations. The majority of particles adopt a single vortex state, with \"bulk\" spins that rotate around a central vortex core. We observed no particles that are in a true single domain state. The results of the micromagnetic simulations challenge some preconceived ideas about the remanence-carrying properties of vortex states. There is often not a simple predictive relationship between the major, intermediate, and minor axes of the particles and the remanence vector imparted in different fields. Although the orientation of the vortex core is determined largely by the ellipsoidal geometry (i.e., parallel to the major axis for prolate ellipsoids and parallel to the minor axis for oblate ellipsoids), the core and remanence vectors can sometimes lie at very large (tens of degrees) angles to the principal axes. The subtle details of the morphology can control the overall remanence state, leading in some cases to a dominant contribution from the bulk spins to the net remanence, with profound implications for predicting the anisotropy of the sample. The particles have very high switching fields (several hundred millitesla), demonstrating their high stability and suitability for paleointensity studies.

Zircon crystals from the Jack Hills, Western Australia, are one of the few surviving mineralogical records of Earth’s first 500 million years and have been proposed to contain a paleomagnetic record of the Hadean geodynamo. A prerequisite for the preservation of Hadean magnetization is the presence of primary magnetic inclusions within pristine igneous zircon. To date no images of the magnetic recorders within ancient zircon have been presented. Here we use high-resolution transmission electron microscopy to demonstrate that all observed inclusions are secondary features formed via two distinct mechanisms. Magnetite is produced via a pipe-diffusion mechanism whereby iron diffuses into radiation-damaged zircon along the cores of dislocations and is precipitated inside nanopores and also during low-temperature recrystallization of radiation-damaged zircon in the presence of an aqueous fluid. Although these magnetites can be recognized as secondary using transmission electron microscopy, they otherwise occur in regions that are indistinguishable from pristine igneous zircon and carry remanent magnetization that postdates the crystallization age by at least several hundred million years. Without microscopic evidence ruling out secondary magnetite, the paleomagnetic case for a Hadean–Eoarchean geodynamo cannot yet been made.

The asteroid Vesta is the smallest known planetary body that has experienced large-scale igneous differentiation. However, it has been previously uncertain whether Vesta and similarly sized planetesimals formed advecting metallic cores and dynamo magnetic fields. Here we show that remanent magnetization in the eucrite meteorite Allan Hills A81001 formed during cooling on Vesta 3.69 billion years ago in a surface magnetic field of at least 2 microteslas. This field most likely originated from crustal remanence produced by an earlier dynamo, suggesting that Vesta formed an advecting liquid metallic core. Furthermore, the inferred present-day crustal fields can account for the lack of solar wind ion-generated space weathering effects on Vesta.