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Ceres is a 940-km-diameter dwarf planet that is predominantly composed of silicates and water ice. In Ceres’ partially differentiated interior, extrusive processes have led to the emplacement on its surface of domes with heights of kilometres. Here we report the analysis of a gravity anomaly detected by the Dawn spacecraft, which is associated with the geologically recent dome Ahuna Mons. By modelling the anomaly with a mass concentration method, we determine that the subsurface structure includes a regional mantle uplift, which we interpret as a plume. This structure is the probable source of fluids forming Ahuna Mons and, together with constraints from the dome’s morphology, indicates a rheological regime corresponding to a slurry of brine and solid particles. We propose that the properties of such a solid–liquid mixture can explain the viscous relaxation and the mineralogy of the dome. The presence of a plume and of slurry material indicate recent convection in a mud-bearing mantle. The inferred slurry extrusion on Ceres differs from the water-dominated cryovolcanism of icy satellites, and so reveals compositional and rheological diversity in extrusive phenomena on planetary surfaces.

Several of the impact craters on Ceres have sets of fractures on their floors. These fractures appear similar to those found within a class of lunar craters referred to as floor‐fractured craters(FFCs). We have cataloged the Ceres FFCs according to the classification scheme designed for the Moon. An analysis of the depth to diameter ratio for Ceres craters shows that, like lunar FFCs, the Ceres FFCs are anomalously shallow. Large (>50 km) Ceres FFCs are most consistent with Class 1 lunar FFCs, while smaller craters on Ceres are more consistent with Class 4 lunar FFCs. This suggests that Ceres FFCs may similarly be undergoing fracturing due to the intrusion of a low‐density material below the craters. While on the Moon (and Mars) the intrusive material is hypothesized to be silicate magma, cryomagmatic intrusions are more likely responsible for the formation of the Ceres FFCs. However, new models suggest that at least some of the FFC fractures may have formed due to the solid‐state flow of a low‐viscosity and low‐density material into the crater wall. Several of the impact craters on the asteroid Ceres have sets of fractures on their floors. It is unclear what could have caused these fractures to form. The only known mechanism for fracturing the floor of impact craters involves volcanism, which is only known to occur on planets like Earth and Mars, not on asteroids like Ceres. This paper explores ways in which the crater floor fractures on Ceres could have formed. Several of the impact craters on Ceres appear similar to a class of lunar craters referred to as floor‐fractured cratersCeres' floor‐fractured craters may have formed due to the intrusion of a low‐density material below the cratersSome of the fractured crater floors may have formed due to the solid‐state flow of a low‐viscosity and low‐density material into the crater

Five decades of observations of Ceres suggest that the dwarf planet has a composition similar to carbonaceous meteorites and may have an ice-rich outer shell protected by a silicate layer. NASA’s Dawn spacecraft has detected ubiquitous clays, carbonates and other products of aqueous alteration across the surface of Ceres, but surprisingly it has directly observed water ice in only a few areas. Here we use Dawn Framing Camera observations to analyse lobate morphologies on Ceres’ surface and we infer the presence of ice in the upper few kilometres of Ceres. We identify three distinct lobate morphologies that we interpret as surface flows: thick tongue-shaped, furrowed flows on steep slopes; thin, spatulate flows on shallow slopes; and cuspate sheeted flows that appear fluidized. The shapes and aspect ratios of these flows are different from those of dry landslides—including those on ice-poor Vesta—but are morphologically similar to ice-rich flows on other bodies, indicating the involvement of ice. Based on the geomorphology and poleward increase in prevalence of these flows, we suggest that the shallow subsurface of Ceres is comprised of mixtures of silicates and ice, and that ice is most abundant near the poles.

Ceres has only a small spin axis tilt (4°), and craters near its rotational poles can experience permanent shadow and trap volatiles, as is the case on Mercury and on Earth's Moon. Topography derived from stereo imaging by the Dawn spacecraft is used to calculate direct solar irradiance that defines the extent of the permanently shadowed regions (PSRs). In the northern polar region, PSRs cover ∼1800 km2or 0.13% of the hemisphere, and most of the PSRs are cold enough to trap water ice over geological time periods. Based on modeling of the water exosphere, water molecules seasonally reside around the winter pole and ultimately an estimated 0.14% of molecules get trapped. Even for the lowest estimates of the amount of available water, this predicts accumulation rates in excess of loss rates, and hence, there should be fresh ice deposits in the cold traps. Permanently shadowed regions (PSRs) identified in the north polar region of CeresNorthern PSR area is about 1800 km2based on topography‐derived illumination modelAccording to exosphere model calculations, fresh ice deposits are expected in the cold traps

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.

Energetic charged particles trapped in planetary radiation belts are hazardous to spacecraft. Planned missions to iron‐rich asteroids with possible strong remanent magnetic fields require an assessment of trapped particles energies. Using laboratory measurements of iron meteorites, we estimate the largest possible asteroid magnetic moment. Although weak compared to moments of planetary dynamos, the small body size may yield strong surface fields. We use hybrid simulations to confirm the formation of a magnetosphere with an extended quasi‐dipolar region. However, the short length scale of the field implies that energetic particle motion would be nonadiabatic, making existing radiation belt theories not applicable. Our idealized particle simulations demonstrate that chaotic motions lead to particle loss at lower energies than those predicted by adiabatic theory, which may explain the energies of transiently trapped particles observed at Mercury, Ganymede, and Earth. However, even the most magnetized asteroids are unlikely to stably trap hazardous particles. Radiation belts are regions in space filled with energetic charged particles trapped by a planetary magnetic field. To date, radiation belts were found around Earth, Jupiter, Saturn, Uranus, and Neptune. Understanding radiation belts is important because they can be hazardous to spacecraft. In addition, their emission, if detected remotely, can reveal a planet's magnetic field. The future exploration of asteroids and exoplanets may lead to the discovery of more magnetized bodies, including the upcoming NASA mission to asteroid (16) Psyche, the largest known metal‐rich planetary object. Existing radiation belt theory was developed for known radiation belts surrounding the large, highly magnetized planets in the solar system. However, the nature of particle trapping should differ for small bodies like asteroids. We examine these differences to provide predictive tools for the existence of belts that can be applied to any kind of magnetosphere. We find a class of bodies that can sustain belt‐like structures but where particle trajectories are chaotic, preventing prolonged stable trapping and associated energization. We show that Mercury and Ganymede's transient trapping is consistent with our predictions. Finally, we show that although asteroids may stably trap low‐energy protons and electrons, even the most strongly magnetized metallic asteroids cannot form belts that pose a risk to typical spacecraft hardware. Meteorite paleomagnetism and hybrid modeling imply that asteroids may form magnetospheres and trap charged particlesPlanning of missions to asteroids requires assessing trapped particle energies, but existing models are not valid for such magnetospheresA new nonadiabatic trapping criterion shows that asteroids should not have hazardous particle radiation belts Meteorite paleomagnetism and hybrid modeling imply that asteroids may form magnetospheres and trap charged particles Planning of missions to asteroids requires assessing trapped particle energies, but existing models are not valid for such magnetospheres A new nonadiabatic trapping criterion shows that asteroids should not have hazardous particle radiation belts

Assessment of Antarctic rebound is complicated by two issues: (1) The total ice volume at Last Glacial Maximum is contentious, with estimates ranging from just a few meters to several tens of meters of equivalent eustatic sea level rise. (2) The late-Holocene mass budget is also uncertain. Space-based geodesy may provide important data in the coming years for estimating the recent ice mass balance state of Antarctica. Toward this end, GPS has an important role for isolating the solid earth movements that are associated with postglacial rebound. Here we provide numerical examples of vertical motions that are predicted by coupling realistic glacial load histories to 20th century ice mass imbalance estimates for the Antarctic Peninsula. The main complexity revealed by these examples is the striking difference among predictions that have an oscillatory mass change during the last 5000 to 50 years, as opposed to those having a continuous (non-oscillatory) mass drawdown of the grounded ice sheet.

An airborne gravity study of the western Weddell sea, east of the Antarctic Peninsula, has shown that floating pack‐ice provides a useful radar altimetric reference surface for altitude and vertical acceleration correction to airborne gravimetry. Airborne gravimetry provides an important alternative to satellite altimetry for the sea‐ice covered regions of the world since satellite altimeters are not designed or intended to provide accurate geoidal heights in areas where significant sea‐ice is present within the radar footprint. Errors in radar corrected airborne gravimetry are primarily sensitive to the variations in the second derivative of the sea‐ice reference surface in the frequency pass‐band of interest. With the exception of imbedded icebergs the second derivative of the pack‐ice surface closely approximates that of the mean sea‐level surface at wavelengths > 10–20 km. With the airborne method the percentage of ice coverage, the mixture of first and multi‐year ice and the existence of leads and pressure ridges prove to be unimportant in determining gravity anomalies at scales of geophysical and geodetic interest, provided that the ice is floating and not grounded. In the Weddell study an analysis of 85 crosstrack miss‐ties distributed over 25 data tracks yields an rms error of 2.2 mGals. Significant structural anomalies including the continental shelf and offsets and lineations interpreted as fracture zones recording the early spreading directions within the Weddell Sea are observed in the gravity map.

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 generated dynamo magnetic fields. Here we describe the magnetic history of the partially differentiated IIE iron meteorite parent body. This is the first planetesimal for which we have a time‐resolved paleomagnetic record constrained by 40Ar/39Ar chronometry spanning several tens of million years (Ma). We find that the core of the IIE parent body generated a dynamo, likely powered by core crystallization, starting before 78 ± 13 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 ( ≳13%–19% core‐to‐body radius ratio depending on the body’s radius), indicating efficient core formation within some partially differentiated planetesimals. Planetesimals were the first planetary bodies that formed in the solar system and meteorites are fragments of these planetesimals. Within the first million years of the solar system, some planetesimals melted and formed metallic cores overlain by a rocky mantles. The loss of heat and release of buoyant fluids generated through the crystallization of these cores could have caused the residual liquid to churn, generating currents that created a magnetic field by the dynamo effect. Some meteorites contain minerals that align their magnetic moments with such magnetic fields, analogous to a compass needle in Earth’s field. Even though the ancient field disappeared billions of years ago, this alignment can still be retained by meteorites today. Because core solidification and generation of magnetic fields are intrinsically related, the magnetic record of meteorites is a powerful proxy for investigating the solidification and thermal history of planetesimals. Here, we present a time‐resolved record captured by three meteorites from the same parent planetesimal of a magnetic field powered by the solidification of their parent planetesimal’s core. It is the most extended record of such fields for which we have absolute ages and supports the hypothesis that some planetesimals efficiently melted and formed significantly large metallic cores. Using IIE iron meteorites, we present the most extended record of dynamo activity on a planetesimal constrained by radiometric datingThis extends the epoch of planetesimal dynamo activity to 160 Ma after solar system formation, indicating protracted core crystallizationThis argues for efficient metal‐silicate separation to form a central metallic core with a radius representing >13%–19% of the body radius Using IIE iron meteorites, we present the most extended record of dynamo activity on a planetesimal constrained by radiometric dating This extends the epoch of planetesimal dynamo activity to 160 Ma after solar system formation, indicating protracted core crystallization This argues for efficient metal‐silicate separation to form a central metallic core with a radius representing >13%–19% of the body radius