The surface of Mars has preserved the record of early environments in which its basaltic crust was altered by liquid water. These aqueous environments have survived in the form of hydrological ...morphologies and alteration minerals, including clays and hydrated salts. Because these minerals probe on Earth aqueous environments compatible with biotic activity, understanding their formation processes on Mars is of great exobiological relevance and also offers insight into Earth's now erased ancient water environments. Using remote sensing, we conducted a large‐scale investigation of the distribution, composition, age, and geomorphic settings of hydrous minerals on Mars, providing a sharpened global view of the early aqueous environments and their evolution with time. Aqueous alteration seems to have produced clays on a planetary scale but these are found to be restricted to the oldest observable terrains on Mars (∼4 Gyr). However, very diverse aqueous environments have also been found which suggest widespread, complex aqueous settings from the surface to kilometric depths, and spanning over 1 Gyr. By building a robust statistical sample of detections, the global trends inferred here attempt to provide a broad view of our current understanding of hydrous minerals on Mars and provide context for more localized, in‐depth analyses. Collectively, these trends suggest that at least transient conditions have existed on Mars which may have been favorable for pre‐biotic to biotic activity.
Key Points
Mars experienced aqueous alteration on a planetary scale
Hydrous mineral diversity reveals diversity of formation environments
Most of the alteration took place ~4 Gyr ago but still occurred 1 Gyr later
Definitive exposures of pristine, ancient crust on Mars are rare, and the finding that much of the ancient Noachian terrain on Mars exhibits evidence of phyllosilicate alteration adds further ...complexity. We have analyzed high‐resolution data from the Mars Reconnaissance Orbiter in the well‐exposed Noachian crust surrounding the Isidis basin. We focus on data from the Compact Reconnaissance Imaging Spectrometer for Mars as well as imaging data sets from High Resolution Imagine Science Experiment and Context Imager. These data show the lowermost unit of Noachian crust in this region is a complex, brecciated unit of diverse compositions. Breccia blocks consisting of unaltered mafic rocks together with rocks showing signatures of Fe/Mg‐phyllosilicates are commonly observed. In regions of good exposure, layered or banded phyllosilicate‐bearing breccia rocks are observed suggestive of pre‐Isidis sedimentary deposits. In places, the phyllosilicate‐bearing material appears as a matrix surrounding mafic blocks, and the mafic rocks show evidence of complex folded relationships possibly formed in the turbulent flow during emplacement of basin‐scale ejecta. These materials likely include both pre‐Isidis basement rocks as well as the brecciated products of the Isidis basin–forming event at 3.9 Ga. A banded olivine unit capped by a mafic unit covers a large topographic and geographic range from northwest of Nili Fossae to the southern edge of the Isidis basin. This olivine‐mafic cap combination superimposes the phyllosilicate‐bearing basement rocks and distinctly conforms to the underlying basement topography. This may be due to draping of the topography by a fluid or tectonic deformation of a previously flatter lying morphology. We interpret the draping, superposed olivine‐mafic cap combination to be impact melt from the Isidis basin–forming event. While some distinct post‐Isidis alteration is evident (carbonate, kaolinite, and serpentine), the persistence of olivine from the time of Isidis basin suggests that large‐scale aqueous alteration processes had ceased by the time this unit was emplaced.
Olivine and Pyroxene Diversity in the Crust of Mars Mustard, J. F; Poulet, F; Gendrin, A ...
Science (American Association for the Advancement of Science),
03/2005, Letnik:
307, Številka:
5715
Journal Article
Recenzirano
Odprti dostop
Datafromthe Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) on the Mars Express spacecraft identify the distinct mafic, rock-forming minerals olivine, low-calcium ...pyroxene (LCP), and high-calcium pyroxene (HCP) on the surface of Mars. Olivine- and HCP-rich regions are found in deposits that span the age range of geologic units. However, LCP-rich regions are found only in the ancient Noachian-aged units, which suggests that melts for these deposits were derived from a mantle depleted in aluminum and calcium. Extended dark regions in the northern plains exhibit no evidence of strong mafic absorptions or absorptions due to hydrated materials.
The structure and composition of cometary constituents, down to their microscopic scale, are critical witnesses of the processes and ingredients that drove the formation and evolution of planetary ...bodies toward their present diversity. On board Rosetta's lander Philae, the Comet Infrared and Visible Analyser (CIVA) experiment took a series of images to characterize the surface materials surrounding the lander on comet 67P/Churyumov-Gerasimenko. Images were collected twice: just after touchdown, and after Philae finally came to rest, where it acquired a full panorama. These images reveal a fractured surface with complex structure and a variety of grain scales and albedos, possibly constituting pristine cometary material.
The composition of the ancient martian crust is a key ingredient in deciphering the environment and evolution of early Mars. We present an analysis of the composition of large craters in the martian ...northern plains based on data from spaceborne imaging spectrometers. Nine of the craters have excavated assemblages of phyllosilicates from ancient, Noachian crust buried beneath the plains' cover. The phyllosilicates are indistinguishable from those exposed in widespread locations in the southern highlands, demonstrating that liquid water once altered both hemispheres of Mars.
We present the distribution of olivine on Mars, derived from spectral parameters based on the 1 µm olivine absorption band. The olivine can be defined with respect to two spectral end‐members: type 1 ...corresponds to olivine with low iron content and/or small grain size and/or small abundance, and type 2, which corresponds to olivine with higher iron content and/or larger grain size and/or larger abundance. The spatial and statistical analysis of the global olivine distribution points out five major geological settings where olivine is detected: (1) Early Hesperian olivine‐bearing smooth crater floors and flat intercrater plains throughout the southern highlands; (2) olivine deposits around the three main basins Argyre, Hellas, and Isidis; (3) olivine in intercrater dunes, crater ejecta, or extended deposits in the northern plains; (4) olivine associated with outcrops and sand in the floor of Valles Marineris; and (5) olivine‐bearing butte outcrops in the vicinity of Hellas. The geological context, the age, and the composition of the olivine detections associated with these five major geological settings are detailed. Their origin and the implication of their occurrence on the composition of the Martian mantle and crust, as well as on the evolution of Mars volcanism are discussed.
Key Points
Global mapping and analysis of olivine bearing deposits
Identification of five major geological settings
Implications on volcanic and internal evolution of Mars
The Hayabusa2 spacecraft arrived at the near-Earth carbonaceous asteroid 162173 Ryugu in 2018. We present Hayabusa2 observations of Ryugu's shape, mass, and geomorphology. Ryugu has an oblate ..."spinning top" shape, with a prominent circular equatorial ridge. Its bulk density, 1.19 ± 0.02 grams per cubic centimeter, indicates a high-porosity (>50%) interior. Large surface boulders suggest a rubble-pile structure. Surface slope analysis shows Ryugu's shape may have been produced from having once spun at twice the current rate. Coupled with the observed global material homogeneity, this suggests that Ryugu was reshaped by centrifugally induced deformation during a period of rapid rotation. From these remote-sensing investigations, we identified a suitable sample collection site on the equatorial ridge.
The recent identification of large deposits of sulphates by remote sensing and in situ observations has been considered evidence of the past presence of liquid water on Mars. Here we report the ...unambiguous detection of diverse phyllosilicates, a family of aqueous alteration products, on the basis of observations by the OMEGA imaging spectrometer on board the Mars Express spacecraft. These minerals are mainly associated with Noachian outcrops, which is consistent with an early active hydrological system, sustaining the long-term contact of igneous minerals with liquid water. We infer that the two main families of hydrated alteration products detected-phyllosilicates and sulphates--result from different formation processes. These occurred during two distinct climatic episodes: an early Noachian Mars, resulting in the formation of hydrated silicates, followed by a more acidic environment, in which sulphates formed.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The structure of the upper layer of a comet is a product of its surface activity. The Rosetta Lander Imaging System (ROLIS) on board Philae acquired close-range images of the Agilkia site during its ...descent onto comet 67P/Churyumov-Gerasimenko. These images reveal a photometrically uniform surface covered by regolith composed of debris and blocks ranging in size from centimeters to 5 meters. At the highest resolution of 1 centimeter per pixel, the surface appears granular, with no apparent deposits of unresolved sand-sized particles. The thickness of the regolith varies across the imaged field from 0 to 1 to 2 meters. The presence of aeolian-like features resembling wind tails hints at regolith mobilization and erosion processes. Modeling suggests that abrasion driven by airfall-induced particle "splashing" is responsible for the observed formations.
We here reassess the global distribution of several key mineral species using the entire OMEGA/Mars Express VIS‐NIR imaging spectrometer data set, acquired from orbit insertion in January 2004 to ...August 2010. Thirty‐two pixels per degree global maps of ferric oxides, pyroxenes and olivines have been derived. A significant filtering process was applied in order to exclude data acquired with unfavorable observation geometries or partial surface coverage with water and CO2 frosts. Because of strong atmospheric variations over the 3.6 Martian years of observations primarily due to the interannual variability of the aerosol opacity, a new filter based on the atmospheric dust opacity calibrated by the Mars Exploration Rovers measurements has also been implemented. The Fe3+absorption features are present everywhere on the surface, with a variety of intensities indicating distinct formation processes. The pyroxene‐bearing regions are localized in low albedo regions, while the bright regions are spectrally comparable to anhydrous nanophase ferric oxides. The expanded data set increases by a factor of about 2, the number of olivine detections reported in previous OMEGA‐based studies. Olivine is mainly detected in three types of areas over the Martian surface: discontinuous patches on the terraces of the three main basins; smooth inter‐crater plains and smooth crater floors throughout the southern highlands; and crater sand dunes, crater ejectas and extended bedrock exposures in the northern plains. Olivine is also detected in the low albedo pyroxene‐bearing dunes surrounding the northern polar cap.
Key Points
Global distribution of several key mineral species of the Martian surface
Use of the full OMEGA data set
Significant filtering process applied on data
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