Dwarf Planet Ceres Research Articles

Long-term orbital and rotational motions of Ceres and Vesta

Context.The dwarf planet Ceres and the asteroid Vesta have been studied by the Dawn space mission. They are the two heaviest bodies of the main asteroid belt and have different characteristics. Notably, Vesta appears to be dry and inactive with two large basins at its south pole. Ceres is an ice-rich body with signs of cryovolcanic activity.Aims.The aim of this paper is to determine the obliquity variations of Ceres and Vesta and to study their rotational stability.Methods.The orbital and rotational motions have been integrated by symplectic integration. The rotational stability has been studied by integrating secular equations and by computing the diffusion of the precession frequency.Results.The obliquity variations of Ceres over [−20 : 0] Myr are between 2° and 20° and the obliquity variations of Vesta are between 21° and 45°. The two giant impacts suffered by Vesta modified the precession constant and could have put Vesta closer to the resonance with the orbital frequency 2s6−sV. Given the uncertainty on the polar moment of inertia, the present Vesta could be in this resonance where the obliquity variations can vary between 17° and 48°.Conclusions.Although Ceres and Vesta have precession frequencies close to the secular orbital frequencies of the inner planets, their long-term rotations are relatively stable. The perturbations of Jupiter and Saturn dominate the secular orbital dynamics of Ceres and Vesta and the perturbations of the inner planets are much weaker. The secular resonances with the inner planets also have smaller widths and do not overlap, contrary to the case of the inner planets.

The Mystery of Ceres' Activity

AbstractIn recent years, the dwarf planet Ceres has been found to release water vapor. Detailed investigation of the surface and subsurface by NASA's Dawn mission reveal localized patches of surface ice and an ice abundance of around 10% in the shallow subsurface, within a meter below the surface. Landis et al. (2019, https://doi.org/10.1029/2018JE005780) quantify the expected sublimation from the surface and subsurface ice reservoirs at Ceres, and the expected evaporation rates are factors of several lower than the observed ones. Although consideration of additional processes may possibly reduce the discrepancy, the origin of Ceres' exosphere is not yet clear.

An aqueously altered carbon-rich Ceres

The surface mineralogy of dwarf planet Ceres appears to be dominated by products of rock–fluid interactions, such as phyllosilicates—some of which are NH4-bearing—and carbonates1–3. Elemental concentrations derived from the inferred mineral mixing fractions, however, do not match measurements of H, C, K and Fe on Ceres4. A complicating factor in assessing Ceres’s unique surface composition is the secular accretion of asteroids typical of chondritic compositions. Here we show that Ceres’s mineral and elemental data can be explained by the presence of carbonaceous chondritic-like materials (~50–60 vol%), possibly due to infalling asteroids, admixed with aqueously altered endogenic materials that contain higher-than-chondritic concentrations of carbon. We find that Ceres’s surface may contain up to 20 wt% of carbon, which is more than five times higher than in carbonaceous chondrites. The coexistence of phyllosilicates, magnetite, carbonates and a high carbon content implies rock–water alteration played an important role in promoting widespread carbon chemistry. These findings unveil pathways for the synthesis of organic matter, with implications for their transport across the Solar System. Infrared and neutron spectroscopic observations by Dawn give contrasting results on the elemental composition of Ceres’s surface, which can be reconciled by assuming that Ceres’s surface contains ~20 wt% of carbon, coming from impacts by carbonaceous asteroids and/or generated by extensive aqueous alteration.

Ahuna Mons lonely no more

Volcanic domes are common in our Solar System but so far only one has been identified on dwarf planet Ceres. New research suggests that numerous volcanic domes may have formed throughout Ceres’s history, indicating that cryovolcanism may have once been more common on the dwarf planet.

Ceres’ opposition effect observed by the Dawn framing camera

Context. The surface reflectance of planetary regoliths may increase dramatically towards zero phase angle, a phenomenon known as the opposition effect (OE). Two physical processes that are thought to be the dominant contributors to the brightness surge are shadow hiding (SH) and coherent backscatter (CB). The occurrence of shadow hiding in planetary regoliths is self-evident, but it has proved difficult to unambiguously demonstrate CB from remote sensing observations. One prediction of CB theory is the wavelength dependence of the OE angular width. Aims. The Dawn spacecraft observed the OE on the surface of dwarf planet Ceres. We aim to characterize the OE over the resolved surface, including the bright Cerealia Facula, and to find evidence for SH and/or CB. It is presently not clear if the latter can contribute substantially to the OE for surfaces as dark as that of Ceres. Methods. We analyze images of the Dawn framing camera by means of photometric modeling of the phase curve. Results. We find that the OE of most of the investigated surface has very similar characteristics, with an enhancement factor of 1.4 and a full width at half maximum of 3° (“broad OE”). A notable exception are the fresh ejecta of the Azacca crater, which display a very narrow brightness enhancement that is restricted to phase angles <0.5° (“narrow OE”); suggestively, this is in the range in which CB is thought to dominate. We do not find a wavelength dependence for the width of the broad OE, and lack the data to investigate the dependence for the narrow OE. The prediction of a wavelength-dependent CB width is rather ambiguous, and we suggest that dedicated modeling of the Dawn observations with a physically based theory is necessary to better understand the Ceres OE. The zero-phase observations allow us to determine Ceres’ visible geometric albedo as pV = 0.094 ± 0.005. A comparison with other asteroids suggests that Ceres’ broad OE is typical for an asteroid of its spectral type, with characteristics that are primarily linked to surface albedo. Conclusions. Our analysis suggests that CB may occur on the dark surface of Ceres in a highly localized fashion. While the results are inconclusive, they provide a piece to the puzzle that is the OE of planetary surfaces.

True polar wander of Ceres due to heterogeneous crustal density

Ceres is the largest body in the main asteroid belt. It was recently explored by the Dawn mission to uncover strong similarities with other icy bodies. The morphological features observed on the surface of Ceres indicate a relatively wide range of water ice concentrations, leading us to investigate the magnitude and distribution of crustal density heterogeneities, and to consider whether they could have caused a reorientation of Ceres. Here, we present three independent and corroborating lines of evidence for the true polar wander of Ceres. Thanks to the global gravity inversion approach applied to the shape and gravity data of Ceres, we find crustal density heterogeneities up to approximately ±0.3 g cm−3, with a prominent positive density anomaly aligned with the equator, in the region of Ahuna Mons. The topography shows the remnants of an equatorial ridge compatible with the position of the palaeo-equator, and indicates that Ceres reoriented by approximately 36°, with the palaeo-pole following an indirect path to the current pole of Ceres. The tectonic patterns generated by the true polar wander are in close agreement with the location and orientation of the Samhain Catenae and Uhola Catenae crustal fractures. These results highlight the complex interior structure and richness of processes taking place in Ceres-scale icy bodies. The dwarf planet Ceres may have reoriented in the past due to a heterogeneously dense crust, a scenario consistent with gravity and topographic data and the distribution of crustal fractures.

Studying the Solar system with the International Pulsar Timing Array

Pulsar-timing analyses are sensitive to errors in the solar-system ephemerides (SSEs) that timing models utilise to estimate the location of the solar-system barycentre, the quasi-inertial reference frame to which all recorded pulse times-of-arrival are referred. Any error in the SSE will affect all pulsars, therefore pulsar timing arrays (PTAs) are a suitable tool to search for such errors and impose independent constraints on relevant physical parameters. We employ the first data release of the International Pulsar Timing Array to constrain the masses of the planet-moons systems and to search for possible unmodelled objects (UMOs) in the solar system. We employ ten SSEs from two independent research groups, derive and compare mass constraints of planetary systems, and derive the first PTA mass constraints on asteroid-belt objects. Constraints on planetary-system masses have been improved by factors of up to 20 from the previous relevant study using the same assumptions, with the mass of the Jovian system measured at 9.5479189(3)$\times10^{-4}$ $M_{\odot}$. The mass of the dwarf planet Ceres is measured at 4.7(4)$\times10^{-10}$ $M_{\odot}$. We also present the first sensitivity curves using real data that place generic limits on the masses of UMOs, which can also be used as upper limits on the mass of putative exotic objects. For example, upper limits on dark-matter clumps are comparable to published limits using independent methods. While the constraints on planetary masses derived with all employed SSEs are consistent, we note and discuss differences in the associated timing residuals and UMO sensitivity curves.

Thermal Stability of Water Ice in Ceres' Craters: The Case of Juling Crater

AbstractIce thermal stability on the surface of the dwarf planet Ceres is an important issue linked to the Herschel observations of water vapor around Ceres. One of these surficial ice deposits is located within the 20‐km crater Juling (35°S, 168°E). The study of water ice exposure in this specific crater is particularly interesting because it has been observed that the water ice abundance changes on a time scale of a few months. To understand the ice behavior, we applied a 3‐D finite element method thermophysical model to the study of Juling crater in order to determine the water ice sublimation rate. We use a detailed shape model of Ceres derived from optical imagery returned by the Framing Camera on board Dawn. We explore the effects of different heliocentric distances and different thermal inertia values, comparing our numerical predictions with the observational evidences returned by VIR and by the Herschel Space Observatory.

Ring‐Mold Craters on Ceres: Evidence for Shallow Subsurface Water Ice Sources

AbstractOne of the main tasks of the Dawn mission is to characterize the potentially ice‐rich crust of the dwarf planet Ceres. Ongoing studies reveal morphological features related to ice‐rich material such as pits or particular landslides. Here we report the identification of ring‐mold craters within the huge impact crater Occator. The Cerean ring‐mold craters exhibit strong morphological similarities to the ring‐mold craters on Mars, where ice‐rich material is thought to be involved in such crater development. We discuss the occurrence of water ice reservoirs in the subsurface and assume that ice‐rich material likely plays an important role in the development of ring‐mold craters on Ceres. The occurrence of ring‐mold craters on the surface of Ceres is not only a sign of water ice reservoirs in the subsurface but can also be used for the study of habitable zones on planetary bodies.

NIR reflectance spectroscopy of hydrated and anhydrous sodium carbonates at different temperatures

Recent space-based observations have revealed or suggested the existence of various types of carbonate salts in several Solar System bodies, such as Mars, Ceres, Enceladus, and Europa. Natrite is the main component of the crater Occator's faculae observed in detail by the Dawn spacecraft on the dwarf planet Ceres. Sodium carbonates are thought to form as precipitates in brines, originating in aqueous environments in the subsurface of Ceres and icy bodies. Here we report about near-infrared (0.8–4.2 μm) reflectance spectroscopic investigations on three compounds, namely natrite (anhydrous Na2CO3), monohydrated sodium carbonate (Na2CO3•H2O, thermonatrite) and decahydrate sodium carbonate (Na2CO3•10H2O, natron). Spectral measurements have been carried out in the overall temperature range 93–279 K, representative of planetary surfaces. The analysis of diagnostic spectral signatures shows different temperature-dependent trends for several band parameters, as well as different behavior as a function of the grain size for a given temperature. While spectra of natrite are characterized by several CO3 absorptions, broad and strong absorption features due to H2O dominate the spectra of heavily hydrated natron. The intermediate sample (monohydrated) shows multiple bands due to the overlap of CO3 and H2O vibrational modes. Our temperature-dependent laboratory spectra are compared with Dawn-VIR spectra of Ceres and with Galileo-NIMS spectra of Europa.

The geology of the Nawish quadrangle of Ceres: The rim of an ancient basin

Herein we present the geology of the Nawish quadrangle, located in the equatorial region of dwarf planet Ceres, named after one of the most prominent craters of the area. Geologic mapping was based on the image mosaics and digital terrain models derived from Dawn Framing Camera data. Interpretation of geologic units was supported by supplemental data, such as the multi spectral color images from the Framing Camera, and the spectral parameters derived from the Visible and Infrared Spectrometer (VIR) data, as well as Dawn gravity data. There is not a primary feature that dominates the geology of Nawish quadrangle, but rather several terrains overlap, and their relations explain the geology of the area. Crater size frequency distributions show that Nawish quadrangle is dominated by two distinct time domains. The central and eastern part of the quadrangle is topographically elevated, which we define as cratered highlands, and contains the older domain. The western lowlands show two younger domains related to impact craters Kerwan and Dantu, including the Kerwan smooth material and Dantu ejecta. This variation of elevation within the Nawish quadrangle is more than the half of the global topographic altitude variation on Ceres. Analysis and comparison of the topography of the Nawish quadrangle with surrounding ones shows that this quadrangle is dominated by the topography of the rim sector of a large, >800 km ancient impact basin, most likely the putative Vendimia Planitia. The Nawish quadrangle thus represents a sector of Ceres which has not undergone large-scale, post-Kerwan, intermediate age-events, but rather represents a place on Ceres where a well-preserved relict of old cerean crust can be studied, together with ejecta from more recent impact events.

Insights into Ceres's evolution from surface composition

AbstractInspired by the recent results of the Dawn mission, thermodynamic models of rock alteration and brine evaporation have been used to help understand the conditions under which water–rock interaction took place within the dwarf planet Ceres. This analysis constrains Ceres's early history and offers a framework within which future observations may be interpreted. A broad range of alteration conditions have been simulated using the Geochemist's Workbench and PHREEQC software, associated with the FREZCHEM model that constrains the consequences of freezing the liquid phase in equilibrium with the observed mineralogical assemblage. Comparison of the modeling results with observed surface mineralogy at Ceres indicates advanced alteration under a relatively high fugacity of hydrogen, a conclusion that is consistent with predictions for, and observations of, large ice‐rich bodies. The simulations suggest production of methane that could help regulate the redox environment and possibly form clathrate hydrates upon freezing of the early ocean. The detection of localized occurrences of natrite (sodium carbonate) at the surface of Ceres provides key constraints on the composition of fluids that are necessarily alkaline. In addition, the combined hydrothermal and freezing simulations suggest that hydrohalite may be abundant in Ceres's subsurface, similar to Earth's polar regions. The global homogeneity of Ceres's surface, made of material formed at depth, suggests a large‐scale formation mechanism, while local heterogeneities associated with impact craters and landslides suggest that some form of sodium carbonate and other salts are accessible in the shallow subsurface.

Spectral analysis of the Cerean geological unit crater central peak material as an indicator of subsurface mineral composition

The dwarf planet Ceres is a heavily cratered rocky body, and complex craters with a central peak are widely observed on its surface. These types of craters form when a large body impacts the surface, generating extreme temperatures and pressures. During the impact event a large volume of rock is raised from the subsurface and a central uplift is formed. The material composing the central uplift is called crater central peak material (ccp) and the spectral analysis of such geologic areas can provide information about the composition of Ceres’ subsurface. Reflectance spectra of 32 ccps, acquired by the VIR spectrometer on board the NASA/Dawn spacecraft, were analyzed and shows absorption bands located at about 2.7, 3.1, 3.4 and 4.0 µm which are also common on the Cerean surface. These absorptions are related, respectively, to Mg-phyllosilicates, NH4-phyllosilicates and Mg/Ca-carbonates.The spectral parameters considered in this work are: spectral slopes estimated between 1.2 µm and 1.9 µm, band depths at 2.7-, 3.1-, 3.4- and 4.0-µm, and band centers near 4.0-µm. The ccps spectral parameters were analyzed in conjunction with other Cerean parameters, such as the estimated depth of excavation of the material composing the central peak, in order to search for correlations and information about Ceres’ subsurface.Central peak material located polewards show stronger 2.7- and 3.1-µm band depths with respect to those at the equatorial region, suggesting that subsurface deposits closer to poles are probably richer in Mg- and NH4-phyllosilicates. The 3.4-µm spectral feature is also deeper in ccps located at poleward latitudes, similar to the phyllosilicates. Conversely, the 4.0-µm band does not show this trend with latitude.An increase in both 3.1- and 3.4-µm band depths with the estimated depth of excavation indicates that the spectral feature at 3.4-µm is the result of different contributions from carbonates and NH4-phyllosilicates, as expected. However, depending on their relative influence, the shape of the 3.4-µm spectral feature can vary.Phyllosilicates and carbonates are the resulting products of aqueous alteration of chondritic material and, given the increasing abundance of such minerals (in particular ammoniated phyllosilicates) with depth of excavation, it is likely that our investigation involved subsurface layers nearby the boundary between the volatile-rich crust and the silicate-rich mantle.Na-carbonate is found in the crater central peak material of Ernutet, Haulani and Ikapati, characterized by an estimated depth of excavation of about 6–9 km, where deposits of sodium carbonates could be locally present.

Composition of dwarf planet Ceres: Constraints from the Dawn spacecraft mission

Composition of dwarf planet Ceres: Constraints from the Dawn spacecraft mission

Ambient and cold‐temperature infrared spectra and XRD patterns of ammoniated phyllosilicates and carbonaceous chondrite meteorites relevant to Ceres and other solar system bodies

AbstractMg‐phyllosilicate‐bearing, dark surface materials on the dwarf planet Ceres have NH4‐bearing materials, indicated by a distinctive 3.06 μm absorption feature. To constrain the identity of the Ceres NH4‐carrier phase(s), we ammoniated ground particulates of candidate materials to compare their spectral properties to infrared data acquired by Dawn's Visible and Infrared (VIR) imaging spectrometer. We treated Mg‐, Fe‐, and Al‐smectite clay minerals; Mg‐serpentines; Mg‐chlorite; and a suite of carbonaceous meteorites with NH4‐acetate to exchange ammonium. Serpentines and chlorites showed no evidence for ammoniation, as expected due to their lack of exchangeable interlayer sites. Most smectites showed evidence for ammoniation by incorporation of NH4+ into their interlayers, resulting in the appearance of absorptions from 3.02 to 3.08 μm. Meteorite samples tested had weak absorptions between 3.0 and 3.1 μm but showed little clear evidence for enhancement upon ammoniation, likely due to the high proportion of serpentine and other minerals relative to expandable smectite phases or to NH4+ complexing with organics or other constituents. The wavelength position of the smectite NH4 absorption showed no variation between IR spectra acquired under dry‐air purge at 25 °C and under vacuum at 25 °C to −180 °C. Collectively, data from the smectite samples show that the precise center wavelength of the characteristic ~3.05 μm v3 absorption in NH4 is variable and is likely related to the degree of hydrogen bonding of NH4‐H2O complexes. Comparison with Dawn VIR spectra indicates that the hypothesis of Mg‐saponite as the ammonium carrier phase is the simplest explanation for observed data, and that Ceres dark materials may be like Cold Bokkeveld or Tagish Lake but with proportionally more Mg‐smectite.

Variations in the amount of water ice on Ceres' surface suggest a seasonal water cycle.

The dwarf planet Ceres is known to host a considerable amount of water in its interior, and areas of water ice were detected by the Dawn spacecraft on its surface. Moreover, sporadic water and hydroxyl emissions have been observed from space telescopes. We report the detection of water ice in a mid-latitude crater and its unexpected variation with time. The Dawn spectrometer data show a change of water ice signatures over a period of 6 months, which is well modeled as ~2-km2 increase of water ice. The observed increase, coupled with Ceres' orbital parameters, points to an ongoing process that seems correlated with solar flux. The reported variation on Ceres' surface indicates that this body is chemically and physically active at the present time.

Dawn mission's search for satellites of Ceres: Intact protoplanets don't have satellites

Upon its approach to orbit the dwarf planet Ceres in early 2015, optical navigation and dedicated satellite search images were acquired with the Dawn mission's framing camera 2. A team of searchers individually processed and examined the images for evidence of objects moving with Ceres. Completeness of search with respect to the space searched was calculated as a function of distance to Ceres and found to be complete down to 15 Ceres radii (Ceres' mean radius is 470 km). Upper limits of detectable magnitude were determined for each observed set of images and an upper limit in size was calculated assuming for the putative objects, Ceres' geometric albedo of 0.11. Nothing was found associated with Ceres down to a radius of 12 m for the most sensitive search, and down to a radius of 323 m for the least sensitive search circumstances. Examination of the physical properties of the 41 largest and most massive main belt asteroids suggests that large asteroids without satellites are intact and their interiors have internal strength. This is consistent with results from the Dawn mission at both Vesta and Ceres. Ceres' volatile-rich composition also is a likely contributor to both the absence of satellites at Ceres and of Ceres meteorites at Earth. These results suggest that collisional disruption creating rubble pile structure is a necessary condition for formation of satellites around main belt asteroids.

Spectral properties and geology of bright and dark material on dwarf planet Ceres

AbstractVariations and spatial distributions of bright and dark material on dwarf planet Ceres play a key role in understanding the processes that have led to its present surface composition. We define limits for “bright” and “dark” material in order to distinguish them consistently, based on the reflectance of the average surface using Dawn Framing Camera data. A systematic classification of four types of bright material is presented based on their spectral properties, composition, spatial distribution, and association with specific geomorphological features. We found obvious correlations of reflectance with spectral shape (slopes) and age; however, this is not unique throughout the bright spots. Although impact features show generally more extreme reflectance variations, several areas can only be understood in terms of inhomogeneous distribution of composition as inferred from Dawn Visible and Infrared Spectrometer data. Additional material with anomalous composition and spectral properties are rare. The identification of the composition and origin of the dark, particularly the darkest material, remains to be explored. The spectral properties and the morphology of the dark sites suggest an endogenic origin, but it is not clear whether they are more or less primitive surficial exposures or excavated subsurface but localized material. The reflectance, spectral properties, inferred composition, and geologic context collectively suggest that the bright and dark material tends to gradually change toward the average surface over time. This could be because of multiple processes, i.e., impact gardening/space weathering, and lateral mixing, including thermal and aqueous alteration, accompanied by changes in composition and physical properties such as grain size, surface temperature, and porosity (compaction).

Constraints on water vapor and sulfur dioxide at Ceres: Exploiting the sensitivity of the Hubble Space Telescope

Far-ultraviolet observations of dwarf-planet (1) Ceres were obtained on several occasions in 2015 and 2016 by the Cosmic Origins Spectrograph (COS) and the Space Telescope Imaging Spectrograph (STIS), both on board the Hubble Space Telescope (HST). We report a search for neutral gas emissions at hydrogen, oxygen and sulfur lines around Ceres from a potential teneous exosphere. No detectable exosphere emissions are present in any of the analyzed HST observations. We apply analytical models to relate the derived upper limits for the atomic species to a water exosphere (for H and O) and a sulfur dioxide exosphere (for S and O), respectively. The H and O upper limits constrain the H2O production rate at the surface to (2−4)×1026 molecules s−1 or lower, similar to or slightly larger than previous detections and upper limits. With low fluxes of energetic protons measured in the solar wind prior to the HST observations and the obtained non-detections, an assessment of the recently suggested sputter-generated water exosphere during solar energetic particle events is not possible. Investigating a sulfur dioxide-based exosphere, we find that the O and S upper limits constrain the SO2 density at the surface to values ∼ 1010 times lower than the equilibrium vapor pressure density. This result implies that SO2 is not present on Ceres’ sunlit surface, contrary to previous findings in HST ultraviolet reflectance spectra but in agreement with the absence of SO2 infrared spectral features as observed by the Dawn spacecraft.

Geologic mapping of the Ac-11 Sintana quadrangle: Assessing diverse crater morphologies

A geologic map at a scale of 1:1,000,000 of the Ac-11 Sintana quadrangle (21–66°S and 0–90°E) from the dwarf planet Ceres and based on data from NASA's Dawn spacecraft, was produced as part of a geologic mapping campaign in order to investigate the surface structure, stratigraphy, composition and surface modifying processes. The Sintana quadrangle is geologically dominated by cratered terrain with morphologically distinct crater types. The most prominent craters, Sintana, Hamori, Jarimba, Tupo, Annona and Darzamat, have complex structures including smooth crater material covering their floors, collapsed crater walls forming terraces, and central ridges. Multiple gravity-driven blocky mass wasting features indicate post-impact crater modification and are indicative of an ice-rich subsurface, in which there is no topographic or structural evidence of endogenic activity visible in the quadrangle. Absolute age estimates suggest that the entire surface in the quadrangle was resurfaced ∼1.1 Ga ago, possibly by Kerwan-related impact-induced melting.