Over the past several decades, orbital observations of lofted dust have revealed the importance of mineral aerosols as a climate forcing mechanism on both Earth and Mars. Increasingly detailed and ...diverse data sets have provided an ever-improving understanding of dust sources, transport pathways, and sinks on both planets, but the role of dust in modulating atmospheric processes is complex and not always well understood. We present a review of orbital observations of entrained dust on Earth and Mars, particularly that produced by the dust-laden structures produced by daytime convective turbulence called “dust devils”. On Earth, dust devils are thought to contribute only a small fraction of the atmospheric dust budget; accordingly, there are not yet any published accounts of their occurrence from orbit. In contrast, dust devils on Mars are thought to account for several tens of percent of the planet’s atmospheric dust budget; the literature regarding martian dust devils is quite rich. Because terrestrial dust devils may temporarily contribute significantly to local dust loading and lowered air quality, we suggest that martian dust devil studies may inform future studies of convectively-lofted dust on Earth.
As on Earth, martian dust devils form most commonly when the insolation reaches its daily and seasonal peak and where a source of loose dust is plentiful. However this pattern is modulated by variations in weather, albedo, or topography, which produce turbulence that can either enhance or suppress dust devil formation. For reasons not well understood, when measured from orbit, martian dust devil characteristics (dimensions, and translational and rotational speeds) are often much larger than those measured from the ground on both Earth and Mars. Studies connecting orbital observations to those from the surface are needed to bridge this gap in understanding. Martian dust devils have been used to remotely probe conditions in the PBL (e.g., CBL depth, wind velocity); the same could be done in remote locations on Earth. Finally, martian dust devils appear to play a major role in the dust cycle, waxing and waning in relative importance and spatial patterns of occurrence with the planet’s orbital state. Orbital studies of terrestrial dust devils would provide a basis for comparative planetology that would broaden the understanding of these dusty vortices on both planets.
History and Applications of Dust Devil Studies Lorenz, Ralph D.; Balme, Matthew R.; Gu, Zhaolin ...
Space Science Reviews,
11/2016, Letnik:
203, Številka:
1-4
Journal Article, Book Review
Recenzirano
Odprti dostop
Studies of dust devils, and their impact on society, are reviewed. Dust devils have been noted since antiquity, and have been documented in many countries, as well as on the planet Mars. As ...time-variable vortex entities, they have become a cultural motif. Three major stimuli of dust devil research are identified, nuclear testing, terrestrial climate studies, and perhaps most significantly, Mars research. Dust devils present an occasional safety hazard to light structures and have caused several deaths.
We investigate the surface morphology of a study area in western Utopia Planitia, Mars, which is characterized by a variety of landforms that resemble those of terrestrial periglacial landscapes. ...Polygonally fractured ground and thermokarst‐like depressions are found to be located in a young mantling deposit with a thickness of several tens of meters. We observe a latitudinal dependence of the degradation of this mantling deposit. Larger depressions, whose floors reveal the underlying basement rocks, cover a higher fraction of the total terrain in the southern part of the study area than in the northern part, indicating a more intense degradation of the mantle in the south. All depressions have an asymmetric cross section in north‐south direction, interpreted to be the result of the different solar radiation on differently oriented slopes. On the basis of our morphological observations, we develop a conceptual model for landscape evolution in western Utopia Planitia. It involves subaerial deposition of a layered, ice‐rich mantle and its subsequent degradation by polygon formation and sublimation. A terrestrial analog to the polygonally fractured mantling deposit and its thermokarst‐like depressions is the Siberian Ice Complex or “Yedoma,” which consists of subaerial ice‐rich deposits and is connected to nonglaciated landscapes with highly continental cold‐climatic environmental conditions. Our comparison suggests that no unusual or exotic processes need to be invoked to explain the current morphology of western Utopia. However, the young age of the deposition and degradation implies climatic excursions in the very recent past on Mars.
Scalloped depressions are a unique martian surface morphology found in the northern and southern hemisphere latitude-dependent dust and ice-rich surface mantles. These features exhibit a distinct ...asymmetric north–south slope profile, characterized by steep pole-facing scarps, flat floors and gentle equator-facing slopes. We examined High Resolution Stereo Camera (HRSC) images of the southern hemisphere to determine their longitudinal distribution, which revealed that a majority of scalloped terrain is located in the region of the southern wall of the Hellas Basin and northern Malea Planum. A detailed map of this area was produced where scallops were found to contour the southern wall of the basin, and where the ice-rich mantle was seen to be thickest. Scalloped terrain is concentrated along the topographic highs near the Amphitrites and Peneus Paterae and areal extent and depth decreases with increasing depth into the basin. We also examined existing hypothesis for the formation and evolution of scalloped depressions using High Resolution Imaging Science Experiment (HiRISE) images and data from the Thermal Emission Imaging System–Infrared (THEMIS–IR) and the Thermal Emission Spectrometer (TES). Our approach provides regional context for the development of scalloped terrains within the southern hemisphere, and offers detailed evidence of scallop depressions forming around small cracks, presumably caused by thermal contraction. Morphometric measurements show that scalloped depressions can be as much as 40
m deep, with typical depths of between 10 and 20
m. Our observations of scallop formation and development in the southern hemisphere support a solar-insolation model proposed by previous researchers (e.g. Morgenstern, A., Hauber, E., Reiss, D., van Gasselt, S., Grosse, G., Schirrmeister, L., 2007. J. Geophys. Res. 112, CiteID E06010; Lefort, A., Russell, P.S., Thomas, N., McEwen, A.S., Dundas, C.M., Kirk, R.L., 2009a. J. Geophys. Res. 114, E04005; Lefort, A., Russell, P.S., Thomas, N., 2009b. Icarus, in press). Observations made using HiRISE images suggest that scalloped depressions most likely form from small cracks in the mantle, which become larger and deeper through sublimation of interstitial ice from within the mantle. Sublimation is likely enhanced on equator-facing slopes because of increased solar insolation, which accounts for the asymmetric slope profile and hemispherical orientation and is demonstrated by THEMIS-IR images. We suggest that sublimation lag deposits can possibly be removed by dust devils or strong slope winds related to the Hellas Basin, offering an explanation as to why scalloped terrain is so abundant only in this area of the southern hemisphere. Daytime maximum summer temperatures suggest that sublimation in the study area of Malea Planum is possible under current conditions if the sublimation lag is removed. While it cannot be ruled out that scalloped terrain in Malea Planum is presently evolving, we attribute the extensive distribution to geologically recent obliquity excursions when conditions were more conducive to mesoscale modification of the ice-rich mantle.
Aeolian processes are the most active processes modifying the surface of Mars under present day climatic conditions. Besides wind streak changes and dune and ripple migrations, active dust devils ...occur frequently leaving numerous tracks on the Martian surface. These dust devil tracks (DDTs) are characterized by albedo changes with respect to their surroundings and are suggested to be caused by erosion of dust exposing coarser grained material. Here we show that DDTs with a cycloidal pattern analyzed in situ in southern Peru are formed by erosion of very coarse sands at the outer margins and its subsequent annular deposition in the central parts of dust devils. Field observations are supported by large-eddy simulations using typical dust devil parameters resembling the cycloidal morphology of the DDTs. Cycloidal DDTs observed on Mars resembling the Peruvian DDTs suggest an equivalent formation mechanism. Our results imply that the formation of DDTs on Mars are not solely due to dust erosion but also depositional processes and dust devils are strong enough to redistribute coarser grained material such as sands; hence they might contribute to the modification of the present day Martian landscape.
•In situ analysis of cycloidal dust devil tracks (DDTs) in southern Peru.•Formation by erosion of coarse sands at the outer margins and its subsequent deposition in the central parts.•Field observations are supported by large-eddy simulations.•Cycloidal DDTs observed on Mars resembling the Peruvian DDTs suggest an equivalent formation mechanism.•Dust devils on Mars might be strong enough to redistribute coarse grained material.
The increased volume, spatial resolution, and areal coverage of high-resolution images of Mars over the past 15 years have led to an increased quantity and variety of small-scale landform ...identifications. Though many such landforms are too small to represent individually on regional-scale maps, determining their presence or absence across large areas helps form the observational basis for developing hypotheses on the geological nature and environmental history of a study area. The combination of improved spatial resolution and near-continuous coverage significantly increases the time required to analyse the data. This becomes problematic when attempting regional or global-scale studies of metre and decametre-scale landforms. Here, we describe an approach for mapping small features (from decimetre to kilometre scale) across large areas, formulated for a project to study the northern plains of Mars, and provide context on how this method was developed and how it can be implemented.
Rather than “mapping” with points and polygons, grid-based mapping uses a “tick box” approach to efficiently record the locations of specific landforms (we use an example suite of glacial landforms; including viscous flow features, the latitude dependant mantle and polygonised ground). A grid of squares (e.g. 20km by 20km) is created over the mapping area. Then the basemap data are systematically examined, grid-square by grid-square at full resolution, in order to identify the landforms while recording the presence or absence of selected landforms in each grid-square to determine spatial distributions. The result is a series of grids recording the distribution of all the mapped landforms across the study area. In some ways, these are equivalent to raster images, as they show a continuous distribution-field of the various landforms across a defined (rectangular, in most cases) area. When overlain on context maps, these form a coarse, digital landform map.
We find that grid-based mapping provides an efficient solution to the problems of mapping small landforms over large areas, by providing a consistent and standardised approach to spatial data collection. The simplicity of the grid-based mapping approach makes it extremely scalable and workable for group efforts, requiring minimal user experience and producing consistent and repeatable results. The discrete nature of the datasets, simplicity of approach, and divisibility of tasks, open up the possibility for citizen science in which crowdsourcing large grid-based mapping areas could be applied.
•Grid mapping allows small landforms to be mapped over large areas.•Grid mapping forms digital landform maps best overlain on context maps.•A tick box approach differentiates grid mapping from traditional points and polygons.•The digital approach makes grid mapping scalable and workable for group efforts.•Grid mapping is ideal for citizen science as it is discrete, easy to use and dividable.
Dust is abundant in the Martian atmosphere and is continuously replenished by the entrainment of material from the surface of the planet. We find that the simple illumination of a dust bed at low ...atmospheric pressure provides a mechanism that efficiently lifts dust particles into the atmosphere. This lifting process is caused by two subtle effects within the dust bed: a greenhouse effect and thermophoresis. Laboratory and microgravity experiments show that the light flux needed for lift to occur is in the same range as that of the solar insolation available on Mars. This mechanism significantly lowers the threshold for dust entrainment by wind stress and may help explain the large amount of suspended dust on Mars overall. Specifically, this lifting process may help provide the initial lift necessary for dust devils and help trigger larger dust storms.
An intravalley paleolake (more than 400 m deep) was detected along the course of Shalbatana Vallis from the evidence of shorelines and the occurrence of a few fan‐delta deposits (including a ...Gilbert‐type delta). The fronts of all the sedimentary deposits strikingly match the same topographic contours (2800 and 3000 m below the Martian datum), indicating the paleolake water levels under which they formed. Also, the corresponding shorelines are visible along the Shalbatana Vallis walls. The peculiar settings of the lake suggest that Shalbatana Vallis was impounded during its final hydrological activity and that ponding of water lasted enough time to allow the formation and evolution of the lacustrine system. Water source is uncertain, but a composite sapping mechanism is hypothesized in order to take into account the amount of water required to excavate, transport, and deposit the materials found in the deposits. Previous works and new crater counting computations indicate that the paleolake was active during the Hesperian epoch; therefore, at that time, surface conditions were different from those of modern Mars and supportive of flow and ponding of water. It is unclear whether the hydrological activity was sustained entirely by a favorable climatic regime and secondary regional factors like volcanism, impact cratering, and tectonism could have also triggered/accelerated the local groundwater activity, implying that the system could have evolved relatively independent from climatic conditions. The latter eventuality and the regional importance of this research advised against an extrapolation of its results to the overall debate about Martian climatic‐geomorphological evolution.
We used a grid‐mapping technique to analyze the distribution of 13 water‐ and ice‐related landforms in Acidalia Planitia as part of a joint effort to study the three main basins in the northern ...lowlands of Mars, that is, Acidalia, Utopia, and Arcadia Planitiae. The landforms were mapped at full Context Camera resolution along a 300‐km‐wide strip from 20°N to 84°N. We identified four landform assemblages: (1) Geologically recent polar cap (massive ice), which superposes the latitude‐dependent mantle (LDM) (LA1); (2) ice‐related landforms, such as LDM, textured terrain, small‐scale polygons, scalloped terrain, large‐scale viscous flow features, and gullies, which have an overlapping distribution (LA2); (3) surface features possibly related to water and subsurface sediment mobilization (LA3; kilometer‐scale polygons, large pitted mounds, small pitted mounds, thumbprint terrain); and (4) irregularly shaped pits with raised rims on equator‐facing slopes. Pits are likely the result of an energetic release of volatiles (H2O, CO2, and CH4), rather than impact‐, volcanism‐, or wind‐related processes. LDM occurs ubiquitously from 44°N to 78°N in Acidalia Planitia. Various observations suggest an origin of air fall deposition of LDM, which contains less ice in the uppermost tens of meters in Acidalia Planitia than in Arcadia and Utopia Planitiae. However, LDM may be thicker and more extended in the past in Acidalia Planitia. The transition between LDM‐free terrain and LDM is situated further north than in Utopia and Arcadia Planitiae, suggesting different past and/or present climatic conditions among the main basins in the northern lowlands.
Plain Language Summary
We studied water and ice‐related landforms in the Acidalia Planitia, Mars. We used a new approach, a grid system of 20 × 20‐km cells, along a 300‐km‐wide strip (east‐west) from latitude 20°N to 84°N (south‐north). This work is a joint effort to study three major basins in the northern plains: Acidalia, Utopia, and Arcadia Planitiae. We conducted a regional mapping of specific landforms at 6 m/pixel resolution data and compared the results to different data products, such as geological maps, topography, radar, and climatic models. We proved that latitude‐dependent mantle occurs from 44°N to 78°N in Acidalia Planitia and has an air fall origin related to past climatic cycles. These deposits are composed of mixture of fine‐grained ice and dust. The distribution of this landform extends further south in Utopia and Arcadia Planitae suggesting different past/present climatic conditions in the northern lowlands.
Key Points
A grid‐mapping approach is demonstrated to be an effective technique to map small‐scale landforms in Acidalia Planitia
LDM begins to occur north of 44 degree N in Acidalia Planitia, a transition that is at a higher latitude than in Utopia and Arcadia Planitiae
Irregular‐shaped pits on equator‐facing scarps suggest an energetic release of volatiles (H2O, CO2, CH4)
Using the new High Resolution Stereo Camera (HRSC) data and other Martian data sets, we reconstructed the hydrological history of an unnamed complex crater in the Xanthe Terra region. The crater ...hosted a lacustrine basin fed by a dense and centripetal drainage system, developed along its inner rim, and by the Tyras Vallis channel. Where the Tyras Vallis opens into the crater, a prominent delta‐like feature is visible, characterized by a central terrace and two small longitudinal scarps. This deposit has been used as sedimentary recorder of the crater lake history and allowed assessment of the overall hydrological evolution. Two major stands of the water level have been inferred at 700 and 550 m above the crater floor, based on the correlation between the morphology and topography of the fan and the crater floor deposits. Our reconstruction reveals a complex sedimentary evolution of the fan, which underwent deltaic and alluvial sedimentation, as a result of the different lake water levels and Tyras Vallis supplies. A dominant erosional evolution of the fan‐delta was determined by the interaction between the fluvial characteristics and basin wave regime. Wave height analysis and morphological comparison with terrestrial analogues support this hypothesis. The lacustrine activity could be chronologically placed between the Late Noachian and the Hesperian. The climatic conditions could have allowed the recharge of the regional groundwater system by precipitation and episodic fluvial activity. However, also heating effects of cratering could have affected the system, rejuvenating or accelerating the recharge of the local aquifer.
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