Mastcam-Z is a multispectral, stereoscopic imaging investigation on the Mars 2020 mission’s
Perseverance
rover. Mastcam-Z consists of a pair of focusable, 4:1 zoomable cameras that provide broadband ...red/green/blue and narrowband 400-1000 nm color imaging with fields of view from 25.6° × 19.2° (26 mm focal length at 283 μrad/pixel) to 6.2° × 4.6° (110 mm focal length at 67.4 μrad/pixel). The cameras can resolve (≥ 5 pixels) ∼0.7 mm features at 2 m and ∼3.3 cm features at 100 m distance. Mastcam-Z shares significant heritage with the Mastcam instruments on the Mars Science Laboratory
Curiosity
rover. Each Mastcam-Z camera consists of zoom, focus, and filter wheel mechanisms and a 1648 × 1214 pixel charge-coupled device detector and electronics. The two Mastcam-Z cameras are mounted with a 24.4 cm stereo baseline and 2.3° total toe-in on a camera plate ∼2 m above the surface on the rover’s Remote Sensing Mast, which provides azimuth and elevation actuation. A separate digital electronics assembly inside the rover provides power, data processing and storage, and the interface to the rover computer. Primary and secondary Mastcam-Z calibration targets mounted on the rover top deck enable tactical reflectance calibration. Mastcam-Z multispectral, stereo, and panoramic images will be used to provide detailed morphology, topography, and geologic context along the rover’s traverse; constrain mineralogic, photometric, and physical properties of surface materials; monitor and characterize atmospheric and astronomical phenomena; and document the rover’s sample extraction and caching locations. Mastcam-Z images will also provide key engineering information to support sample selection and other rover driving and tool/instrument operations decisions.
This study aims to quantify the spatial distribution of terrestrial volcanic rootless cones and ice mounds for the purpose of identifying analogous Martian features. Using a nearest neighbor (NN) ...methodology, we use the statistics R (ratio of the mean NN distance to that expected from a random distribution) and c (a measure of departure from randomness). We interpret R as a measure of clustering and as a diagnostic for discriminating feature types. All terrestrial groups of rootless cones and ice mounds are clustered (R: 0.51–0.94) relative to a random distribution. Applying this same methodology to Martian feature fields of unknown origin similarly yields R of 0.57–0.93, indicating that their spatial distributions are consistent with both ice mound or rootless cone origins, but not impact craters. Each Martian impact crater group has R ≥ 1.00 (i.e., the craters are spaced at least as far apart as expected at random). Similar degrees of clustering preclude discrimination between rootless cones and ice mounds based solely on R values. However, the distribution of pairwise NN distances in each feature field shows marked differences between these two feature types in skewness and kurtosis. Terrestrial ice mounds (skewness: 1.17–1.99, kurtosis: 0.80–4.91) tend to have more skewed and leptokurtic distributions than those of rootless cones (skewness: 0.54–1.35, kurtosis: −0.53–1.13). Thus NN analysis can be a powerful tool for distinguishing geological features such as rootless cones, ice mounds, and impact craters, particularly when degradation or modification precludes identification based on morphology alone.
Cryovolcanic resurfacing is a popular mechanism to explain relatively young surface units on icy satellites of Jupiter, Saturn, Uranus, and Neptune. Prior to the Galileo data acquired between 1996 ...and 2001, Europa was thought to have undergone significant cryovolcanic resurfacing, facilitated by a global ocean beneath the icy surface. However, close examination of Galileo data at resolutions much better than those of Voyager images show that many of the features previously thought to be cryovolcanic are commonly best explained by other formative mechanisms, including tectonism and diapirism. In this study, I present an examination of the characteristics of a variety of Europan surface features for which effusive cryovolcanism is a possible origin, including apparently lobate “flows,” certain elliptical to circular lenticulae, and low‐lying, smooth, low‐albedo surfaces. A review of cryovolcanic eruption theory, together with Galileo data analysis of Europan surface geology and composition, indicates that cryovolcanism is a viable, though not unequivocal, explanation for some of these features. Some constraints on cryomagma properties and lithospheric structure are offered for these cases. The presence of small‐volume, low‐viscosity effusions is supported by observations and modeling. Some positive relief lenticulae could represent more viscous effusions, although diapirism may be a preferable explanation. However, strong evidence is lacking for cryovolcanic resurfacing on a large scale. On the basis of our experience with Galileo images of Europa (and Ganymede), Voyager‐era inferences for widespread cryovolcanism on icy satellites may be overstated and will need to be carefully reexamined in the light of new data from upcoming spacecraft missions.
The study of ~1300 juvenile and lithic blocks from a Vulcanian phase of the 1912 eruption of Novarupta provides new insight into the state of the magma as an eruption passes from sustained Plinian to ...dome growth. Blocks that were predominantly ballistically ejected were measured and sampled within an ~2–3-km radius from vent and supply a picture of a dynamic and complex shallow conduit prior to magma fragmentation in repeated small explosions. Extreme conduit heterogeneity is expressed in the diverse range of dacitic block types, including pumiceous, dense, banded, and variably welded breccia clasts, all with varied degrees of surface breadcrusting. We present new maps of block lithology and size, making Episode IV the most thoroughly mapped Vulcanian deposit to date. Sectorial regions rich in specific lithologies together with the block size data suggest multiple, small explosions. Modeling of block trajectories to reproduce the field data indicates that ejection velocities range from 50 to 124 m/s with a median of ~70 m/s. We propose that individual explosions originated from a heterogeneous shallow conduit characterized both by the juxtaposition of magma domains of contrasting texture and vesiculation state and by the intimate local mingling of different textures on short vertical and horizontal length scales at the contacts between these domains. In our model, each explosion disrupted the conduit to only shallow depths and tapped diverse, localized pockets within the conduit. This contrasts with existing models for repetitive Vulcanian explosions, and suggests that the dynamics of Episode IV were more complex than a simple progressive top-down evacuation of a horizontally stratified conduit.
We present a combined geomorphologic, multispectral, and geochemical analysis of crater floor rocks in Jezero crater based on data obtained by the Mast Camera Zoom and SuperCam instruments onboard ...the NASA Mars 2020 Perseverance rover. The combined data from this analysis together with the results of a comparative study with geologic sites on Earth allows us to interpret the origins of rocks exposed along the Artuby ridge, a ∼900 m long scarp of lower Máaz formation rocks. The ridge exposes rocks belonging to two morphologically distinct members, Artuby and Rochette, both of which have basaltic composition and are spectrally indistinguishable in our analysis. Artuby rocks consist of morphologically distinct units that alternate over the ridge, bulbous, hummocky, layers with varying thicknesses that in places appear to have flowed over underlying strata, and sub‐planar thinner laterally continuous layers with variable friability. The Rochette member has a massive appearance with pronounced pitting and sub‐horizontal partings. Our findings are most consistent with a primary igneous emplacement as lava flows, through multiple eruptions, and we propose that the thin layers result either from preferential weathering, interbedded ash/tephra layers, ʻaʻā clinker layers, or aeolian deposition. Our analyses provide essential geologic context for the Máaz formation samples that will be returned to Earth and highlight the diversity and complexity of geologic processes on Mars not visible from orbit.
Plain Language Summary
Characterization of the landing site for the Mars 2020 Perseverance rover mission yields insight into early solar system processes and provides essential context for Mars Sample Return. Here we have investigated crater floor rocks in Jezero crater that are exposed along a scarp called Artuby ridge with the Mast Camera Zoom (Mastcam‐Z) and SuperCam instruments onboard the Perseverance rover. The Artuby ridge displays a characteristically layered set of rocks with a basaltic composition that are spectrally and chemically indistinguishable in our investigation. We compare our observations from Jezero with well‐understood geologic deposits on Earth, from Hawaiʻi and New Mexico. We find that terrestrial lava flows can have complex interiors that replicate many features that we see in Mastcam‐Z images of the Artuby ridge, and thus, that the series of rocks exposed along the Artuby ridge are dominated by lava flows originating through multiple eruptions. There are a number of layers and textures of the rocks in our investigation that may not have originated as lava flows, that instead may be products of weathering, interbedding of lava and volcanic ash/tephra, or wind‐borne sediment deposition. Our results highlight the diversity of geologic units on Mars not visible from orbit.
Key Points
We investigated Artuby and Rochette member rocks of the Máaz formation in Jezero crater using Perseverance's Mast Camera Zoom and SuperCam data
Complex knobbly, foliated, vesicular, and layered lithologies are most consistent with lava flows originating through multiple eruptions
The Máaz formation in Jezero crater could be unrelated to the regional Circum–Isidis capping unit
It has been proposed that Jupiter's satellite Europa currently possesses a global subsurface ocean of liquid water. Galileo gravity data verify that the satellite is differentiated into an outer H2O ...layer about 100 km thick but cannot determine the current physical state of this layer (liquid or solid). Here we summarize the geological evidence regarding an extant subsurface ocean, concentrating on Galileo imaging data. We describe and assess nine pertinent lines of geological evidence: impact morphologies, lenticulae, cryovolcanic features, pull‐apart bands, chaos, ridges, surface frosts, topography, and global tectonics. An internal ocean would be a simple and comprehensive explanation for a broad range of observations; however, we cannot rule out the possibility that all of the surface morphologies could be due to processes in warm, soft ice with only localized or partial melting. Two different models of impact flux imply very different surface ages for Europa; the model favored here indicates an average age of ∼50 Myr. Searches for evidence of current geological activity on Europa, such as plumes or surface changes, have yielded negative results to date. The current existence of a global subsurface ocean, while attractive in explaining the observations, remains inconclusive. Future geophysical measurements are essential to determine conclusively whether or not there is a liquid water ocean within Europa today.
This study aims at quantifying the spatial distribution of cones within rootless cone groups (RCGs). Our data set consists of (1) seven Icelandic RCGs (identified through field investigations), (2) ...seven candidate RCGs on Mars (identified through Mars Orbiter Camera (MOC) and Thermal Emission Imaging System (THEMIS) images), and (3) four groups of impact craters on Mars (also identified through MOC and THEMIS images) to determine if they can be remotely distinguished from the RCGs purely on the basis of their spatial distribution. Several independent statistical techniques are used, including nearest neighbor analysis, analysis of variance (ANOVA), and linear alignment detection analysis. Our results indicate that the spatial distribution of each RCG is not random: Within a cone group, cones preferentially form near existing cones. The presence of at least one significant linear cone alignment in each RCG (and strong linear alignments in some groups) suggests that rootless cones form as the surface signature of preferred lava pathways. An ANOVA on mean nearest neighbor distances reveals the Martian cone groups to be statistically indistinguishable from the Icelandic RCGs, supporting existing interpretations that they represent rootless cone groups. A similar ANOVA showed that the Martian cone groups do not resemble the Martian impact crater clusters studied: The impact craters have significantly greater nearest neighbor distances and show no evidence of aggregation within a crater group.
We describe the discrete ballistic and wind‐advected products of a small, but exceptionally well‐characterized, explosive eruption of wall‐rock‐derived pyroclasts from Kīlauea volcano on 19 March ...2008 and, for the first time, integrate the size distribution of the two subpopulations to reconstruct the true size distribution of a population of pyroclasts as it exited from the vent. Based on thinning and fining relationships, the wind‐advected fraction had a mass of 6.1 × 105 kg and a thickness half distance of 110 m, placing it at the bottom end of the magnitude and intensity spectra of pyroclastic falls. The ballistic population was mapped, in the field and by using structure‐from‐motion techniques, to a diameter of > 10–20 cm over an area of ~0.1 km2, with an estimated mass of 1 × 105 kg. Initial ejection velocities of 50–80 m/s were estimated from inversion of isopleths. The total grain size distribution was estimated by using a mass partitioning of 98% of wind‐advected material and 2% of ballistics, resulting in median and sorting values of −1.7ϕ and 3.1ϕ. It is markedly broader than those calculated for the products of magmatic explosive eruptions, because the grain size of 19 March 2008 clast population is unrelated to a volcanic fragmentation event and instead was “inherited” from a population of talus clasts that temporary blocked the vent prior to the eruption. Despite a conspicuous near‐field presence, the ballistic subpopulation has only a minor influence on the grain size distribution because of its rapid thinning and fining away from source.
Key Points
Data for ballistic blocks and wind‐advected components merged as the first total grain size for an entire pyroclastic fall deposit
Ballistic data (via a combination of field measurements and structure from motion) has little influence on total grain size distribution
Grain size distribution of “wall‐rock” particles may be inherited and not due to explosive fragmentation
We investigate cryomagmatic mechanisms for the formation of the diffuse low-albedo margins of triple bands and haloes associated with elliptical lenticulae on Europa. One mechanism involves explosive ...venting of a gas-particle spray derived from a subsurface body of volatile-bearing water. Assuming the dark features represent cryoclastic deposits erupted from a medial or central vent, modeling the dynamics of the eruptive plumes indicates that eruption velocities of 30 to 250 m s
−1 and volatile contents of 0.1 to 20 wt% are required to produce deposits having the observed dimensions. Calculated heights for ballistic plumes range from <1 to ∼25 km. As an alternative mechanism, we consider conductive heating of lithospheric ice by a subsurface heat source (e.g., a warm ice diapir or cryomagmatic intrusion), which promotes enhanced sublimation of surface ice, producing local enrichment of nonice material. An analytical model describing a constant-temperature, infinite heat source places lower bounds on the time scales required to produce a detectable feature. A numerical treatment of more realistic geometries and boundary conditions allows cooling of the heat source to be modeled. We find that the thermal model satisfactorily explains features with the dimensions of minor lineaments and lenticulae haloes (a few kilometers) over time intervals of ∼10
4 to 10
5 years. The formation of a sublimation lag deposit proceeds rapidly once the ice temperature exceeds a threshold of ∼130 K. However, for triple bands measuring up to 25 km in width, additional heat sources, such as repeated or multiple intrusions, are necessary to reproduce the observed dimensions. This is consistent with the observation that well-developed triple bands typically have multiple medial ridge sets, each of which may represent a discrete tabular heat source. Although neither the volcanic nor intrusive/thermal model can be ruled out at this stage, the latter is a more satisfactory explanation for some characteristics of the low-albedo features analyzed in this study.
Infrared wavelength observations of lo by the Galileo spacecraft show that at least 12 different vents are erupting lavas that are probably hotter than the highest temperature basaltic eruptions on ...Earth today. In at least one case, the eruption near Pillan Patera, two independent instruments on Galileo show that the lava temperature must have exceeded 1700 kelvin and may have reached 2000 kelvin. The most likely explanation is that these lavas are ultramafic (magnesium-rich) silicates, and this idea is supported by the tentative identification of magnesium-rich orthopyroxene in lava flows associated with these high-temperature hot spots.
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