Large asteroid impacts have long been attributed to imparting long‐lived heat in the upper crust, as well as widespread fracturing and porosity. When an impact occurs on or near an ocean environment, ...displaced water rushes back filling the crater and percolating down into the fractured crust. The significant heat and fracturing from impact allow for extensive hydrothermal activity. Hydrothermal alteration has been observed at the 180 km Chicxulub impact structure in Yucatán, Mexico. Previous studies estimate widespread hydrothermal transport and activity within the Chicxulub structure, but these processes are largely dependent on the assumed post‐impact permeability distribution. In this work, we present an impact simulation that tracks fragmentation as well as the generation of porosity and permeability during the Chicxulub impact event. The generation of porosity during tensile failure results in final porosities (up to 40%) that are up to a factor of 4 higher than previous models and in better agreement with drill core data. We find that both fragmentation and porosity contribute to overall permeability of the Chicxulub structure. Estimated permeabilities (up to 10−14 m2) are greater than measured values from drill cores because of the contribution from large‐scale fragmentation, which cannot be resolved in cm‐diameter drill cores. The larger porosities and permeabilities computed in this work suggest that the volume of hydrothermal activity generated by Chicxulub were 10 times more than previously estimated for Chicxulub and 100 times more than the Yellowstone caldera.
Plain Language Summary
The Chicxulub impact event that led to the extinction of the dinosaurs 66 million years ago hit the Earth on a carbonate platform leaving a 180 km wide impact crater onto what is now Yucatán, Mexico. The impact caused widespread fracturing of the carbonate crust and underlying granite. The extent of this fracturing and what effect it had on hydrothermal activity is of great interest. Several drill cores have been unearthed from within the crater by scientific expeditions. In this work, we build on previous impact simulations of the event using an updated code to model and estimate the extent of fragmentation in the carbonate and granite. Specifically, we model the formation of porosity (void space) and fragmented materials and estimate permeability (the interconnectedness of void space or fractures) and compare with what has been measured and observed in the drill cores for various regions within the crater. We find that the impact likely created more permeable space than what is estimated from drill core data. More permeable space may suggest more hydrothermal activity could be sustained as water from the ocean rushed back into the fractured, warm crust. Hydrothermal systems from the Chicxulub impact may have been 100 times larger than the modern Yellowstone Caldera.
Key Points
We simulate impact‐induced porosity with iSALE that is comparable to porosity measured in two different drill cores
We find the permeabilities introduced by the Chicxulub impact event may be greater than those measured from the M0077A and Yax‐1 drill cores
The output from this work will be useful and necessary for constraining the longevity and evolution of hydrothermal systems
•New approached to detect olivine on the Vesta surface have been developed.•We confirm detections in the Arruntia and Bellicia regions.•New detections were found in the Albana and Pomponia ...regions.•Different scenarios about the olivine origin on Vesta are discussed.
The discovery of olivine on Vesta’s surface by the VIR imaging spectrometer onboard the Dawn space mission has forced us to reconsider our views of Vestan petrogenetic models. Olivines were expected to be present in the interior of Vesta: in the mantle of a vertically layered body as invoked by the magma ocean models, or at the base (or within) the mantle–crust boundary as proposed by fractionation models. Olivines have been detected by VIR-Dawn in two wide areas near Arruntia and Bellicia, regions located in the northern hemisphere. Interestingly, these olivine-rich terrains are far from the Rheasilvia and the more ancient Veneneia basins, which are expected to have excavated the crust down to reach the mantle. In this work we present our attempts to identify other undetected olivine rich areas on Vesta by using spectral parameters sensitive to olivine such as the Band Area Ratio (BAR) and other specific parameters created for the detection of olivines on Mars (forsterite, fayalite and a generic olivine index). As a preliminary step we calibrated these parameters by means of VIS–IR spectra of different HED meteorite samples: behaviors versus sample grain size and albedo were analyzed and discussed. We selected the BAR and the Forsterite Index as the best parameters that can be used on Vesta. A cross-correlation analysis has been applied in order to detect olivine signature on the VIR hyperspectral cubes. These detections have then been confirmed by an anti-correlation analysis between the BAR and one of the olivine parameters, independent of the first method applied.
In agreement with the recent discovery, Arruntia and Bellicia were found to be as the most olivine-rich areas, i.e. where the parameter values are strongest. In addition we detected 6 new regions, all but one located in the Vesta north hemisphere. This result confirms again that the old petrogenetic models cannot be straightforwardly applied to Vesta and should be reshaped in the view of these new detections. An alternative and very recent option can be represented by the model according to which surface “eruption” of material from the mantle, including olivine can reach the surface of Vesta.
•A photo-geologic map of Ceres North Pole Ac-1 Asari quadrangle has been produced with Dawn Framing Camera images at a resolution of 35 m/pixel.•Lobate materials are associated with impact cratering ...and are possibly formed by high speed flows. Their abundance does not appear to be latitude dependent.•Approximately 1-km large bright areas are found on the floor of few craters, within permanently shadowed regions, and might originate from infall of exogenic material.
The Dawn Framing Camera repeatedly imaged Ceres’ North Pole quadrangle (Ac-1 Asari, latitudes >66°N) at a resolution of ∼35 m/pixel through a panchromatic filter, enabling the derivation of a digital terrain model (DTM) and an ortho-rectified mosaic. Using this dataset, a photo-geologic map and stratigraphy, complemented with absolute model ages of impact craters, were produced. We identified the following key surface features: an ancient 4.5 km high isolated dome with a non-impact origin; recent lobate materials on crater interiors possibly formed as high-speed flows of collapsed rim material; and recent bright areas in permanently shadowed regions (PSRs), which we interpret as ice accumulation mostly by infall of exogenic material. Crater morphologies and dimensions do not differ from those in other quadrangles, suggesting the widespread influence of a rheologically weak target during the crater formation process. There is a paucity of lobate materials associated with impact cratering, in contrast to previous identifications with lower spatial resolution imagery.
During its first two flybys of Mercury, the MESSENGER spacecraft acquired images confirming that pervasive volcanism occurred early in the planet's history. MESSENGER's third Mercury flyby revealed a ...290-kilometer-diameter peak-ring impact basin, among the youngest basins yet seen, having an inner floor filled with spectrally distinct smooth plains. These plains are sparsely cratered, postdate the formation of the basin, apparently formed from material that once flowed across the surface, and are therefore interpreted to be volcanic in origin. An irregular depression surrounded by a halo of bright deposits northeast of the basin marks a candidate explosive volcanic vent larger than any previously identified on Mercury. Volcanism on the planet thus spanned a considerable duration, perhaps extending well into the second half of solar system history.
The Dawn spacecraft mission has provided extensive new and detailed data on Vesta that confirm and strengthen the Vesta–howardite–eucrite–diogenite (HED) meteorite link and the concept that Vesta is ...differentiated, as derived from earlier telescopic observations. Here, we present results derived by newly calibrated spectra of Vesta. The comparison between data from the Dawn imaging spectrometer—VIR—and the different class of HED meteorites shows that average spectrum of Vesta resembles howardite spectra. Nevertheless, the Vesta spectra at high spatial resolution reveal variations in the distribution of HED‐like mineralogies on the asteroid. The data have been used to derive HED distribution on Vesta, reported in Ammannito et al. (2013), and to compute the average Vestan spectra of the different HED lithologies, reported here. The spectra indicate that, not only are all the different HED lithologies present on Vesta, but also carbonaceous chondritic material, which constitutes the most abundant inclusion type found in howardites, is widespread. However, the hydration feature used to identify carbonaceous chondrite material varies significantly on Vesta, revealing different band shapes. The characteristic of these hydration features cannot be explained solely by infalling of carbonaceous chondrite meteorites and other possible origins must be considered. The relative proportion of HEDs on Vesta's surface is computed, and results show that most of the vestan surface is compatible with eucrite‐rich howardites and/or cumulate or polymict eucrites. A very small percentage of surface is covered by diogenite, and basaltic eucrite terrains are relatively few compared with the abundance of basaltic eucrites in the HED suite. The largest abundance of diogenitic material is found in the Rheasilvia region, a deep basin, where it clearly occurs below a basaltic upper crust. However, diogenite is also found elsewhere; although the depth to diogenite is consistent with one magma ocean model, its lateral extent is not well constrained.
Mercury's images obtained by the 1974 Mariner 10 flybys show extensive cratered landscapes degraded into vast knob fields, known as chaotic terrain (AKA hilly and lineated terrain). For nearly half a ...century, it was considered that these terrains formed due to catastrophic quakes and ejecta fallout produced by the antipodal Caloris basin impact. Here, we present the terrains' first geologic examination based on higher spatial resolution MESSENGER (MErcury Surface Space ENvironment GEochemistry and Ranging) imagery and laser altimeter topography. Our surface age determinations indicate that their development persisted until ~1.8 Ga, or ~2 Gyrs after the Caloris basin formed. Furthermore, we identified multiple chaotic terrains with no antipodal impact basins; hence a new geological explanation is needed. Our examination of the Caloris basin's antipodal chaotic terrain reveals multi-kilometer surface elevation losses and widespread landform retention, indicating an origin due to major, gradual collapse of a volatile-rich layer. Crater interior plains, possibly lavas, share the chaotic terrains' age, suggesting a development associated with a geothermal disturbance above intrusive magma bodies, which best explains their regionality and the enormity of the apparent volume losses involved in their development. Furthermore, evidence of localized, surficial collapse, might reflect a complementary, and perhaps longer lasting, devolatilization history by solar heating.
We present global lithological maps of the Vestan surface based on Dawn mission's Visible InfraRed (VIR) Spectrometer acquisitions with a spatial sampling of 200 m. The maps confirm the results ...obtained with the data set acquired by VIR with a spatial sampling of 700 m, that the reflectance spectra of Vesta's surface are dominated by pyroxene absorptions that can be interpreted within the context of the distribution of howardites, eucrites, and diogenites (HEDs). The maps also partially agree with the ground and Hubble Space Telescope observations: they confirm the background surface being an assemblage of howardite or polymict eucrite, as well as the location of a diogenitic‐rich spot; however, there is no evidence of extended olivine‐rich regions in the equatorial latitudes. Diogenite is revealed on the Rheasilvia basin floor, indicating that material of the lower crust/mantle was exposed. VIR also detected diogenites along the scarp of Matronalia Rupes, and the rims of Severina and a nearby, unnamed crater, and as ejecta of Antonia crater. The diogenite distribution is fully consistent with petrological constraints; although the mapped distribution does not provide unambiguous constraints, it favors the hypothesis of a magma ocean.
The peculiar object P/2010 A2 was discovered in January 2010 and given a cometary designation because of the presence of a trail of material, although there was no central condensation or coma. The ...appearance of this object, in an asteroidal orbit (small eccentricity and inclination) in the inner main asteroid belt attracted attention as a potential new member of the recently recognized class of main-belt comets. If confirmed, this new object would expand the range in heliocentric distance over which main-belt comets are found. Here we report observations of P/2010 A2 by the Rosetta spacecraft. We conclude that the trail arose from a single event, rather than a period of cometary activity, in agreement with independent results. The trail is made up of relatively large particles of millimetre to centimetre size that remain close to the parent asteroid. The shape of the trail can be explained by an initial impact ejecting large clumps of debris that disintegrated and dispersed almost immediately. We determine that this was an asteroid collision that occurred around 10 February 2009.
We present observations obtained with the Near Infrared Spectrograph on JWST of the five Jupiter Trojans that will be visited by the Lucy spacecraft—the Patroclus–Menoetius binary, Eurybates, Orus, ...Leucus, and Polymele. The measured 1.7–5.3 μ m reflectance spectra, which provide increased wavelength coverage, spatial resolution, and signal-to-noise ratio over previous ground-based spectroscopy, reveal several distinct absorption features. We detect a broad OH band centered at 3 μ m that is most prominent on the less-red objects Eurybates, Patroclus–Menoetius, and Polymele. An additional absorption feature at 3.3–3.6 μ m, indicative of aliphatic organics, is systematically deeper on the red objects Orus and Leucus. The collisional fragment Eurybates is unique in displaying an absorption band at 4.25 μ m that we attribute to bound or trapped CO _2 . Comparisons with other solar system small bodies reveal broad similarities in the 2.7–3.6 μ m bands with analogous features on Centaurs, Kuiper Belt objects (KBOs), and the active asteroid 238P. In the context of recent solar system evolution models, which posit that the Trojans initially formed in the outer solar system, the significant attenuation of the 2.7–3.6 μ m absorption features on Trojans relative to KBOs may be the result of secondary thermal processing of the Trojans’ surfaces at the higher temperatures of the Jupiter region. The CO _2 band manifested on the surface of Eurybates suggests that CO _2 may be a major constituent in the bulk composition of Trojans, but resides in the subsurface or deeper interior and is largely obscured by refractory material that formed from the thermophysical processes that were activated during their inward migration.
Abstract
The Lucy Mission accomplishes its science during a series of five flyby encounters with seven Trojan asteroid targets. This mission architecture drives a concept of operations design that ...maximizes science return, provides redundancy in observations where possible, features autonomous fault protection, and utilizes onboard target tracking near closest approach. These design considerations reduce risk during the relatively short time-critical periods when science data is collected. The payload suite consists of a color camera and infrared imaging spectrometer, a high-resolution panchromatic imager, and a thermal infrared spectrometer. The mission design allows for concurrent observations of all instruments. Additionally, two spacecraft subsystems will also contribute to the science investigations: the Terminal Tracking Cameras will obtain wide field-of-view imaging near closest approach to determine the shape of each of the Trojan targets and the telecommunication subsystem will carry out Doppler tracking of the spacecraft to determine the mass of each of the Trojan targets.
PDF
