Icy Terrain Research Articles

Dark ray craters on Ganymede: Impactor or endogenous origin

Through the spectral analysis of Galileo Near Infrared Mapping Spectrometer (NIMS) observations we now have a better understanding of the origin of dark ray craters (DRCs) on Ganymede. The analysis of NIMS observations show that DRCs are not a single compositional group, and at least some DRCs are the result of the excavation of endogenous material. DRCs overlying bright terrain may be entirely due to the excavation of the darker Ganymede hydrate material; the dark ejecta associated with the Tammuz impact is an example with its rays composed entirely of Ganymede hydrate. In contrast, three DRCs on the trailing hemisphere imaged by NIMS (Kittu, Amon, and Mir craters) show that a third component is present, with the ejecta being a mixture of water-ice, the hydrated non-ice material endogenous to Ganymede, and a less-hydrated, red, non-ice component. The spectrum of this second non-ice component is consistent with hydrated carbonaceous material, implying either a primitive impactor origin or excavation of primordial Ganymede non-ice material. This carbonaceous component is required at an abundance of about 40 to 50% in the ejecta of the three DRCs, assuming discrete mixing. It is absent in icy terrain but often present in regiones unassociated with DRCs, ranging in abundance in that terrain from 0 to again, about 50%. Its abundance in older, more primordial terrain suggests the carbonaceous material is endogenous to Ganymede. Thus, excavation of subsurface material appears capable of accounting for the diversity of DRCs. Additional spectral imaging observations of these and other DRCs are needed to verify this conclusion.

Discrete element modeling of planetary ice analogs: mechanical behavior upon sintering

Potentially habitable icy Ocean Worlds, such as Enceladus and Europa, are scientifically compelling worlds in the solar system and high-priority exploration targets. Future robotic exploration of Enceladus and Europa by in-situ missions would require a detailed understanding of the surface material and of the complex lander-surface interactions during locomotion or sampling. To date, numerical modeling approaches that provide insights into the icy terrain’s mechanical behavior have been lacking. In this work, we present a Discrete Element Model of porous planetary ice analogs that explicitly describes the microstructure and its evolution upon sintering. The model dimension is tuned following a Pareto-optimality analysis, the model parameters’ influence on the sample strength is investigated using a sensitivity analysis, and the model parameters are calibrated to experiments using a probabilistic method. The results indicate that the friction coefficient and the cohesion energy density at the particle-scale govern the macroscopic properties of the porous ice. Our model reveals a good correspondence between the macroscopic and bond strength evolutions, suggesting that the strengthening of porous ice results from the development of a large-scale network due to inter-particle bonding. This work sheds light on the multi-scale nature of the mechanics of planetary ice analogs and points to the importance of understanding surface strength evolution upon sintering to design robust robotic systems.Graphic abstract

Improving Visual Feature Extraction in Glacial Environments

Glacial science could benefit tremendously from autonomous robots, but previous glacial robots have had perception issues in these colorless and featureless environments, specifically with visual feature extraction. This translates to failures in visual odometry and visual navigation. Glaciologists use near-infrared imagery to reveal the underlying heterogeneous spatial structure of snow and ice, and we theorize that this hidden near-infrared structure could produce more and higher quality features than available in visible light. We took a custom camera rig to Igloo Cave at Mt. St. Helens to test our theory. The camera rig contains two identical machine vision cameras, one which was outfitted with multiple filters to see only near-infrared light. We extracted features from short video clips taken inside Igloo Cave at Mt. St. Helens, using three popular feature extractors (FAST, SIFT, and SURF). We quantified the number of features and their quality for visual navigation by comparing the resulting orientation estimates to ground truth. Our main contribution is the use of NIR longpass filters to improve the quantity and quality of visual features in icy terrain, irrespective of the feature extractor used.

Applicability of an ultra-long-range terrestrial laser scanner to monitor the mass balance of Muz Taw Glacier, Sawir Mountains, China

Glacier mass balance is a key component of glacier monitoring programs. Information on the mass balance of Sawir Mountains is poor due to a dearth of in-situ measurements. This paper introduces the applicability of an ultra-long-range terrestrial laser scanner (TLS) to monitor the mass balance of Muz Taw Glacier, Sawir Mountains, China. The Riegl VZ ® -6000 TLS is exceptionally well-suited for measuring snowy and icy terrain. Here, we use TLS to create repeated high spatiotemporal resolution DEMs, focusing on the annual mass balance (June 2, 2015 to July 25, 2016). According to TLS-derived high spatial resolution point clouds, the front variation (glacier retreat) of Muz Taw Glacier was 9.3 m. The mean geodetic elevation change was 4.55 m at the ablation area. By comparing with glaciological measurements, the glaciological elevation change of individual stakes and the TLS-derived geodetic elevation change of corresponding points matched closely, and the calculated balance was −3.864±0.378 m w.e.. This data indicates that TLS provides accurate results and is therefore suitable to monitor mass balance evolution of Muz Taw Glacier.

Ice-rich (periglacial) vs icy (glacial) depressions in the Argyre region, Mars: a proposed cold-climate dichotomy of landforms

On Mars, so-called “scalloped depressions” are widely observed in Utopia Planitia (UP) and Malea Planum (MP). Typically, they are rimless, metres- to decametres-deep, incised sharply, tiered inwardly, polygonised and sometimes pitted. The depressions seemingly incise terrain that is icy and possibly thermokarstic, i.e. produced by the thermal destabilisation of the icy terrain. Agewise, the depressions are thought to be relatively youthful, originating in the Late Amazonian Epoch. Here, we report the presence of similar depressions in the Argyre region (AR) (30–60° S; 290–355° E). More importantly, we separate and differentiate these landforms into two groups: (ice-rich) periglacial depressions (Type-1); and, (icy) glacial depressions (Type-2a-c). This differentiation is presented to the Mars community for the first time. Based on a suite of morphological and geological characteristics synonymous with ice-complexes in the Lena Peninsula (eastern Russia) and the Tuktoyaktuk Coastlands (Northwest Territories, Canada), we propose that the Type-1 depressions are ice-rich periglacial basins that have undergone volatile depletion largely by sublimation and as the result of thermal destabilisation. In keeping with the terms and associated definitions derived of terrestrial periglacial-geomorphology, ice-rich refers to permanently frozen-ground in which ice lenses or segregation ice (collectively referenced as excess ice) have formed. We suggest that the depressions are the product of a multi-step, cold-climate geochronology: Atmospheric precipitation and surface accumulation of an icy mantle during recent high obliquities. Regional or local triple-point conditions and thaw/evaporation of the mantle, either by exogenic forcing, i.e. obliquity-driven rises of aerial and sub-aerial temperatures, or endogenic forcing, i.e. along Argyre impact-related basement structures. Meltwater migration into the regolith, at least to the full depth of the depressions. Freeze-thaw cycling and the formation of excess ice. Sublimation of the excess ice and depression formation as high obliquity dissipates and near-surface ice becomes unstable. The Type-2 depressions exhibit characteristics suggestive of (supra-glacial) dead-ice basins and snow/ice suncups observed in high-alpine landscapes on Earth, e.g. the Swiss Alps and the Himalayas. Like the Type-1 depressions, the Type-2 depressions could be the work of sublimation; however, the latter differ from the former in that they seem to develop within a glacial-like icy mantle that blankets the surface rather than within an ice-rich and periglacially-revised regolith at/near the surface. Interestingly, the Type-2 depressions overlie the Type-1 depressions at some locations. If the periglacial/glacial morphological and stratigraphical dichotomy of depressions is valid, then this points to recent glaciation at some locations within the AR being precursed by at least one episode of periglaciation. This also suggests that periglaciation has a deeper history in the region than has been thought hitherto. Moreover, if the hypothesised differences amongst the Argyre-based depressions are mirrored in Utopia Planitia and Malea Planum, then perhaps this periglacial-glacial dichotomy and its associated geochronology are as relevant to understanding late period landscape-evolution in these two regions as it is in the AR?

Possible ice-wedge polygons and recent landscape modification by “wet” periglacial processes in and around the Argyre impact basin, Mars

The Argyre basin and associated rim-materials in the southern hemisphere of Mars are ancient, having been formed by the impact of a large body ∼4Gya. This notwithstanding, the regional landscape continues to be altered by a multiplicity of geological and geomorphological processes.Three landforms, whose close spatial-association is identified in a new geological map of the Argyre region (∼290–360°E; ∼30–72°S), feature prominently in the list of very Late Amazonian Epoch alterations:(a)Small-sized (⩽∼20m in diameter) and unsorted polygons that exhibit metre to sub-metre elevated margins or shoulders, giving them a low-centred appearance; in “wet” permafrost environments on Earth low-centred polygons (LCPs) often are underlain by ice-wedges.(b)Gullies, seemingly formed by “wet” flow(s) and incised by the LCPs.(c)A putative (possibly ice-rich) latitude-dependent mantle (LDM) that underlies the LCPs and spatially-convergent “wet” gullies in all of our observations.These landforms occur from the middle to the high (near-polar) latitudes of the region and overlie geological units of all ages.Hitherto, the presence of the LCPs has been reported only fleetingly in the literature and only in as much as they have been observed on the walls of a few scalloped depressions in mid-Utopia Planitia. By contrast, we report the ubiquitous occurrence of the LCPs in and around the Argyre impact-basin on gully-margins and adjacent slopes as well as on relatively-flat inter-crater terrain.On the basis of three separate but related lines of reasoning we hypothesise that ice wedges could be present beneath LCP margins in our study region. If we are correct then these LCP sites are geomorphological expressions of boundary conditions that were relatively warm and wet in the recent past.First, substantial ice-wedging in permafrost environments on Earth requires the availability of meltwater. If, as some researchers propose, the formation of some “wet” gullies at the martian mid-latitudes is induced by the localised (slope-side and crater-wall) thaw of the underlying LDM at the gully sites themselves, then meltwater also should be available for ice-wedging and the formation of LCPs at these sites. Interestingly, LCPs are observed on gully-channel walls as expected if meltwater is associated with gully formation; however, in some instances the LCPs are also observed on the slope-side terrain that extends for hundreds of metres beyond the channel walls and even above the gully alcoves. This suggests that the distribution of icy terrain affected by thaw could be much more substantial than has been suggested hitherto.Second, LCPs that are identical in shape and scale to the slope-side LCPs are observed on relatively flat inter-crater terrain (also underlain by the LDM) that is distal from the “wet” gullies. By contrast, here, their distribution extends for kilometres. This too could be indicative of meltwater being more extensive in the regional landscape than most workers have thought possible.Third, on Earth the “dryness” or the “wetness” of a permafrost environment determines whether LCP margins are underlain by sand or by ice. When the observed LCPs and major deposits of sand in the study region are plotted on our new map of the Argyre impact-basin, we see that these deposits are rarely proximal. On the other hand, the LDM underlies the LCPs in all instances and, if modified by thaw, seems to be a likelier source of margin fill for the LCPs than sand.

Frozen in Time: Gender, Fan Culture, and a Young Widow’s Icy Terrain

In the opening scenes of Douglas Sirk’s 1955 melodrama All That Heaven Allows (Hunter & Sirk, 1955), the precocious, college-aged daughter of the movie’s heroine describes the ancient Egyptian custom of “walling up the widow alive in the funeral chambers of her dead husband along with his other possessions, the theory being that she was a possession, too.” When she adds that “it doesn’t happen any more,” her widowed mother, played by Jane Wyman, asks wryly, “Doesn’t it?” As the film depicts, metaphorical walls still circumscribe the cultural and economic spaces inhabited by widows. This occurs in particularly telling ways for those whose late husbands, and/or the manner in which they died, are public and iconic. According to Bird (1992), supermarket tabloids sanitized the image of the late President John F. Kennedy after revelations of his marital infidelity, preferring to render him as the “heroic lover” while...

An overview of the descent and landing of the Huygens probe on Titan

Titan, Saturn's largest moon, is the only Solar System planetary body other than Earth with a thick nitrogen atmosphere. The Voyager spacecraft confirmed that methane was the second-most abundant atmospheric constituent in Titan's atmosphere, and revealed a rich organic chemistry, but its cameras could not see through the thick organic haze. After a seven-year interplanetary journey on board the Cassini orbiter, the Huygens probe was released on 25 December 2004. It reached the upper layer of Titan's atmosphere on 14 January and landed softly after a parachute descent of almost 2.5 hours. Here we report an overview of the Huygens mission, which enabled studies of the atmosphere and surface, including in situ sampling of the organic chemistry, and revealed an Earth-like landscape. The probe descended over the boundary between a bright icy terrain eroded by fluvial activity--probably due to methane-and a darker area that looked like a river- or lake-bed. Post-landing images showed centimetre-sized surface details.

Unusual Radar Echoes from the Greenland Ice Sheet

Airborne radar images of part of the Greenland ice sheet reveal icy terrain whose radar properties are unique among radar-studied terrestrial surfaces but resemble those of Jupiter's icy Galilean satellites. The 5.6- and 24-centimeter-wavelength echoes from the Greenland percolation zone, like the 3.5- and 13-centimeter-wavelength echoes from the icy satellites, are extremely intense and have anomalous circular and linear polarization ratios. However, the detailed subsurface configurations of the Galilean satellite regoliths, where heterogeneities are the product of prolonged meteoroid bombardment, are unlikely to resemble that within the Greenland percolation zone, where heterogeneities are the product of seasonal melting and refreezing.