Global Surveyor Mars Orbiter Camera Research Articles

The seasonal and spatial distribution of textured dust storms observed by Mars Global Surveyor Mars Orbiter Camera

Local and regional dust storms observed by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) exhibit three main types of textures in their visible top structures which we describe as “pebbled”, “puffy”, and “plume-like.” In this paper, we present the temporal and spatial distribution of each texture type. There is a pause in activity near the solstices for all three texture types, but the pause is more pronounced for pebbled and plume-like dust storms than for puffy dust storms. The average size of each texture type is usually much larger during the northern summer and fall (Ls=90–270°) than during the rest of the Martian year. Although all three textures types can be observed at all latitudes, plume-like dust storms tend to dominate the northern mid-latitudes, pebbled dust storms tend to dominate the southern mid-latitudes, and puffy dust storms tend to dominate the low latitudes. During the 2001 global dust storm in Mars Year 25, we found a progression from a combination of all three texture types in the early stage to mostly plume-like dust storms in the expansion and decay phases.

IDENTIFYING SURFACE CHANGES ON HRSC IMAGES OF THE MARS SOUTH POLAR RESIDUAL CAP (SPRC)

The surface of Mars has been an object of interest for planetary research since the launch of Mariner 4 in 1964. Since then different cameras such as the Viking Visual Imaging Subsystem (VIS), Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC), and Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) and High Resolution Imaging Science Experiment (HiRISE) have been imaging its surface at ever higher resolution. The High Resolution Stereo Camera (HRSC) on board of the European Space Agency (ESA) Mars Express, has been imaging the Martian surface, since 25th December 2003 until the present-day. HRSC has covered 100 % of the surface of Mars, about 70 % of the surface with panchromatic images at 10-20 m/pixel, and about 98 % at better than 100 

IDENTIFYING SURFACE CHANGES ON HRSC IMAGES OF THE MARS SOUTH POLAR RESIDUAL CAP (SPRC)

Abstract. The surface of Mars has been an object of interest for planetary research since the launch of Mariner 4 in 1964. Since then different cameras such as the Viking Visual Imaging Subsystem (VIS), Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC), and Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) and High Resolution Imaging Science Experiment (HiRISE) have been imaging its surface at ever higher resolution. The High Resolution Stereo Camera (HRSC) on board of the European Space Agency (ESA) Mars Express, has been imaging the Martian surface, since 25th December 2003 until the present-day. HRSC has covered 100 % of the surface of Mars, about 70 % of the surface with panchromatic images at 10-20 m/pixel, and about 98 % at better than 100 m/pixel (Neukum et. al., 2004), including the polar regions of Mars. The Mars polar regions have been studied intensively recently by analysing images taken by the Mars Express and MRO missions (Plaut et al., 2007). The South Polar Residual Cap (SPRC) does not change very much in volume overall but there are numerous examples of dynamic phenomena associated with seasonal changes in the atmosphere. In particular, we can examine the time variation of layers of solid carbon dioxide and water ice with dust deposition (Bibring, 2004), spider-like channels (Piqueux et al., 2003) and so-called Swiss Cheese Terrain (Titus et al., 2004). Because of seasonal changes each Martian year, due to the sublimation and deposition of water and CO2 ice on the Martian south polar region, clearly identifiable surface changes occur in otherwise permanently icy region. In this research, good quality HRSC images of the Mars South Polar region are processed based on previous identification as the optimal coverage of clear surfaces (Campbell et al., 2015). HRSC images of the Martian South Pole are categorized in terms of quality, time, and location to find overlapping areas, processed into high quality Digital Terrain Models (DTMs) and Orthorectified Images (ORIs) and projected into polar stereographic projection using DLR (Deutsches Zentrum für Luft- und Raumfahrt; German Aerospace Center)’s VICAR and GIS software with modifications developed by Kim & Muller (2009). Surface changes are identified in the Mars SPRC region and analysed based on their appearance in the HRSC images.

Orbital monitoring of martian surface changes

A history of martian surface changes is documented by a sequence of global mosaics made up of Mars Global Surveyor Mars Orbiter Camera daily color images from 1999 to 2006, together with a single mosaic from the Mars Reconnaissance Orbiter Mars Color Imager in 2009. These observations show that changes in the global albedo patterns of Mars take place by a combination of dust storms and strong winds. Many of the observed surface changes took place along the tracks of seasonally repeating winter dust storms cataloged by Wang and Richardson (2015). These storms tend to sweep dust towards the equator, progressively shifting albedo boundaries and continuing surface changes that began before the arrival of MGS. The largest and most conspicuous changes took place during the global dust storm of 2001 (MY 25), which blanketed Syrtis Major, stripped dust from the Tharsis region, and injected dust into Solis Planum. High wind speeds but low wind stresses are predicted in Syrtis, Tharsis and Solis by the NASA Ames GCM. Frequent changes in these regions show that dust accumulations are quickly removed by stronger winds that are not predicted by the GCM, but may result from smaller-scale influences such as unresolved topography.

The production of small primary craters on Mars and the Moon

We model the primary crater production of small (D<100m) primary craters on Mars and the Moon using the observed annual flux of terrestrial fireballs. From the size–frequency distribution (SFD) of meteor diameters, with appropriate velocity distributions for Mars and the Moon, we are able to reproduce martian and lunar crater-count chronometry systems (isochrons) in both slope and magnitude. We include an atmospheric model for Mars that accounts for the deceleration, ablation, and fragmentation of meteors. We find that the details of the atmosphere or the fragmentation of the meteors do not strongly influence our results. The downturn in the crater SFD from atmospheric filtering is predicted to occur at D∼10–20cm, well below the downturn observed in the distribution of fresh craters detected by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) or the Mars Reconnaissance Orbiter (MRO) Context Camera (CTX). Crater counts are conducted on the ejecta blanket of Zunil crater and the interior of Pangboche crater on Mars and North Ray and Cone craters on the Moon. Our model isochrons produce a similar slope and age estimate for the formation of Zunil crater as the Hartmann production function (∼1Ma). We derive an age of 35.1Ma for Pangboche when accounting for the higher elevation (>20km higher than Zunil), a factor ∼2 younger than estimated using the Hartmann production function which assumes 6mbar surface pressure. We estimate ages of 52.3Ma and 23.9Ma for North Ray and Cone crater respectively, consistent with cosmic ray exposure ages from Apollo samples. Our results indicate that the average cratering rate has been constant on these bodies over these time periods. Since our Monte Carlo simulations demonstrate that the existing crater chronology systems can be applied to date young surfaces using small craters on the Moon and Mars, we conclude that the signal from secondary craters in the isochrons must be relatively small at these locations, as our Monte Carlo model only generates primary craters.

The origin, evolution, and trajectory of large dust storms on Mars during Mars years 24–30 (1999–2011)

Mars Daily Global Maps (MDGM) derived from the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) and Mars Reconnaissance Orbiter (MRO) Mars Color Imager (MARCI) are used to study the distribution and evolution of large dust storms over the period from Mars years 24–30 (1999–2001). Large storms are defined here as discrete dust events visible in image sequences extending over at least 5 sols (Mars days) and where the dust covers areas beyond the origination region. A total of 65 large dust storms meeting these criteria are identified during the observational period and all are observed during the Ls=135–30° seasonal window. Dust storms originating in the northern and southern hemispheres appear to form two distinct families. All but two of the storms originating in the northern hemisphere are observed in two seasonal windows at Ls=180–240° and Ls=305–350°; while all but two of those originating in the southern hemisphere are observed during Ls=135–245°.None of the large dust storms originating in the northern hemisphere are observed to develop to global scale, but some of them develop into large regional storms with peak area >1×107km2 and duration on the order of several weeks. In comparison, large dust storms originating in the southern hemisphere are typically much smaller, except notably in the two cases that expanded to global scale (the 2001 and 2007 global storms).Distinct locations of preferred storm origination emerge from the dust storm image sequences, including Acidalia, Utopia, Arcadia and Hellas. A route (trajectory) ‘graph’ for the observed sequences is provided. The routes are highly asymmetric between the two hemispheres. In the south, for non-global dust storms, the main routes are primarily oriented eastwest, whereas in the north, the routes are primarily north–south and zonally-concentrated into meridional channels. In a few impressive cases, storms originating in the northern hemisphere are observed to “flush” through Acidalia and Utopia, across the equator, and then branch in the low- and mid-southern latitudes. The origin of the 2007 global dust storm is ambiguous from the imaging data. Immediately prior to the global storm, a dust storm sequence from Chryse is identified. This storm’s connection to the explosive expansion observed to start from Noachis/West Hellas is unclear due to image coverage. This paper further identifies and describes three different styles of dust storm development, which we refer to as “consecutive dust storms”, “sequential activation” and “merging.” The evolution of a given dust storm sequence can exhibit different combinations of these growth styles at different stages of development. Dust storm sequences can overlap in time, which makes them good candidate to grow into larger scale.

Curvilinear features in the southern hemisphere observed by Mars Global Surveyor Mars Orbiter Camera

We have used the complete set of Mars Global Surveyor (MGS) Mars Daily Global Maps (MDGMs) to study martian weather in the southern hemisphere, focusing on curvilinear features, including frontal events and streaks. “Frontal events” refer to visible events that are morphologically analogous to terrestrial baroclinic storms. MDGMs show that visible frontal events were mainly concentrated in the 210–300°E (60–150°W) sector and the 0–60°E sector around the southern polar cap during L s = 140–250° and L s = 340–60°. The non-uniform spatial and temporal distributions of activity were also shown by MGS Thermal Emission Spectrometer transient temperature variations near the surface. “Streaks” refer to long curvilinear features in the polar hood or over the polar cap. They are an indicator of the shape of the polar vortex. Streaks in late winter usually show wavy segments between the 180° meridian and Argyre. Model results suggest that the zonal wave number m = 3 eastward traveling waves are important for their formation.

Model for Formation of Dunes at the North Martian Pole

The Mars Global Surveyor Mars Orbiter Camera (MOC) took images of a series of strange horseshoe-shaped dunes at the North Martian pole in 2004. These dunes would be formed due to the strong Martian winds whose pattern is different from that on the Earth. We study the cause of the formation of these dunes and make a model for them. In this model, wind speed near the north Martian pole can be evaluated based on the shape of the dunes. We also estimate the surpassing speed of dunes of different sizes.

North polar frontal clouds and dust storms on Mars during spring and summer

The complete archive of Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) Mars Daily Global Maps (MDGM) are used to study north polar clouds and dust storms that exhibit frontal structures during the spring and summer ( L s 0–180°). Results show that frontal events generally follow the edge of the polar cap during spring and mid/late summer with a gap in the distribution in early summer. The exact duration and timing of the gap vary from year to year. Ten to twenty percent of spring and summer time frontal events exhibit complex morphologies. Distinct temperature signatures are associated with features observed in images in many but not all cases. The general travel paths of the frontal events are eastward around the polar cap. Westward paths exist only at the edge of the polar cap in late spring/early summer. Occasionally, the paths curve toward or away from the polar cap in certain longitude sectors.

Characteristics of large Martian dust devils using Mars Odyssey Thermal Emission Imaging System visual and infrared images

A search for Martian dust devils has been carried out, using Mars Odyssey Thermal Emission Imaging System (THEMIS) visible‐wavelength images. Simultaneous THEMIS thermal infrared wavelength images were then processed and analyzed to investigate the thermal properties of the dust devils observed; 3079 images were checked, concentrating on northern spring, summer, and autumn (LS from 0° to 270°, 20°S to 50°N). Mars Express High Resolution Stereo Camera, Mars Global Surveyor Mars Orbiter Camera, and other THEMIS visible images were used for comparison to potentially rule out any ambiguous geological features. Eight clear examples of dust devils have been found in five separate images, with a comparable number of unconfirmed possible devils. The rarity of dust devils observed is believed to result from a combination of the difficulty in identifying dust devils in medium resolution THEMIS data and the fact that the Mars Odyssey orbit flyover local time is later in the afternoon than would be optimum for dust devil searching. The temporal distribution of dust devil activity appears to be weighted more toward later afternoon, compared to Earth, but this may be a sampling effect due to size variation with time of sol, greater coverage later in the sol, or the small‐number statistics. The thermal infrared images indicate that the lofted dust in the column is cooler than the surrounding surface and must be equilibrating with the atmosphere in the dust devil. This energy transfer is estimated to be about 10% of the heat flux energy that is available to drive the systems. The ground shadowed by the dust column also appears colder than the surroundings, because of reduced solar illumination. From the visible‐wavelength images, the shadows of the dust columns were used to estimate the column opacity, which in turn gave estimates of the dust loadings, which ranged from 1.9 × 10−5 to 1.5 × 10−4 kg m−3, similar to lander‐based observations. No thermal or visible trails are associated with the dust devils, indicating that the surface equilibrates quickly after the devil has passed and that track counting as a dust devil survey technique must underestimate dust devil populations and consequently dust loading calculations, confirming previous work.

Surface albedo observations at Gusev Crater and Meridiani Planum, Mars

During the Mars Exploration Rover mission, the Pancam instrument has periodically acquired large‐scale panoramic images with its broadband (739 ± 338 nm) filter in order to estimate the Lambert bolometric albedo of the surface along each rover's traverse. In this work we present the full suite of such estimated albedo values measured to date by the Spirit and Opportunity rovers along their traverses in Gusev Crater and Meridiani Planum, respectively. We include estimated bolometric albedo values of individual surface features (e.g., outcrops, dusty plains, aeolian bed forms, wheel tracks, light‐toned soils, and crater walls) as well as overall surface averages of the 43 total panoramic albedo data sets acquired to date. We also present comparisons to estimated Lambert albedo values taken from the Mars Global Surveyor Mars Orbiter Camera (MOC) along the rovers' traverses, and to the large‐scale bolometric albedos of the sites from the Viking Orbiter Infrared Thermal Mapper (IRTM) and Mars Global Surveyor/Thermal Emission Spectrometer (TES). The ranges of Pancam‐derived albedos at Gusev Crater (0.14 to 0.25) and in Meridiani Planum (0.10 to 0.18) are in good agreement with IRTM, TES, and MOC orbital measurements. These data sets will be a useful tool and benchmark for future investigations of albedo variations with time, including measurements from orbital instruments like the Context Camera and High Resolution Imaging Science Experiment on Mars Reconnaissance Orbiter. Long‐term, accurate albedo measurements could also be important for future efforts in climate modeling as well as for studies of active surface processes.

Ultrahigh resolution topographic mapping of Mars with MRO HiRISE stereo images: Meter‐scale slopes of candidate Phoenix landing sites

The objectives of this paper are twofold: first, to report our estimates of the meter‐to‐decameter‐scale topography and slopes of candidate landing sites for the Phoenix mission, based on analysis of Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images with a typical pixel scale of 3 m and Mars Reconnaissance Orbiter (MRO) High Resolution Imaging Science Experiment (HiRISE) images at 0.3 m pixel−1 and, second, to document in detail the geometric calibration, software, and procedures on which the photogrammetric analysis of HiRISE data is based. A combination of optical design modeling, laboratory observations, star images, and Mars images form the basis for software in the U.S. Geological Survey Integrated Software for Imagers and Spectrometers (ISIS) 3 system that corrects the images for a variety of distortions with single‐pixel or subpixel accuracy. Corrected images are analyzed in the commercial photogrammetric software SOCET SET (® BAE Systems), yielding digital topographic models (DTMs) with a grid spacing of 1 m (3–4 pixels) that require minimal interactive editing. Photoclinometry yields DTMs with single‐pixel grid spacing. Slopes from MOC and HiRISE are comparable throughout the latitude zone of interest and compare favorably with those where past missions have landed successfully; only the Mars Exploration Rover (MER) B site in Meridiani Planum is smoother. MOC results at multiple locations have root‐mean‐square (RMS) bidirectional slopes of 0.8–4.5° at baselines of 3–10 m. HiRISE stereopairs (one per final candidate site and one in the former site) yield 1.8–2.8° slopes at 1‐m baseline. Slopes at 1 m from photoclinometry are also in the range 2–3° after correction for image blur. Slopes exceeding the 16° Phoenix safety limit are extremely rare.

Context Camera Investigation on board the Mars Reconnaissance Orbiter

The Context Camera (CTX) on the Mars Reconnaissance Orbiter (MRO) is a Facility Instrument (i.e., government‐furnished equipment operated by a science team not responsible for design and fabrication) designed, built, and operated by Malin Space Science Systems and the MRO Mars Color Imager team (MARCI). CTX will (1) provide context images for data acquired by other MRO instruments, (2) observe features of interest to NASA's Mars Exploration Program (e.g., candidate landing sites), and (3) conduct a scientific investigation, led by the MARCI team, of geologic, geomorphic, and meteorological processes on Mars. CTX consists of a digital electronics assembly; a 350 mm f/3.25 Schmidt‐type telescope of catadioptric optical design with a 5.7° field of view, providing a ∼30‐km‐wide swath from ∼290 km altitude; and a 5000‐element CCD with a band pass of 500–700 nm and 7 μm pixels, giving ∼6 m/pixel spatial resolution from MRO's nearly circular, nearly polar mapping orbit. Raw data are transferred to the MRO spacecraft flight computer for processing (e.g., data compression) before transmission to Earth. The ground data system and operations are based on 9 years of Mars Global Surveyor Mars Orbiter Camera on‐orbit experience. CTX has been allocated 12% of the total MRO data return, or about ≥3 terabits for the nominal mission. This data volume would cover ∼9% of Mars at 6 m/pixel, but overlapping images (for stereo, mosaics, and observation of changes and meteorological events) will reduce this area. CTX acquired its first (instrument checkout) images of Mars on 24 March 2006.

Recent low-latitude freeze–thaw on Mars

Outside polar latitudes, features corresponding to surface thaw have yet to be identified on Mars. The youthful gully landforms observed at mid-high latitude [Malin, M., Edgett, K., 2000. Science 288, 2330–2335] are the nearest candidate, but the source (and nature) of the gully carving agent remains controversial [e.g., Musselwhite, D.S., Swindle, T.D., Lunine, J.I., 2001. Geophys. Res. Lett. 28, 1283–1285; Mellon, M.T., Phillips, R.J., 2001. J. Geophys. Res. 106, 1–15; Knauth, L.P., Burt, D.M., 2002. Icarus 158, 267–271; Costard, F., Forget, F., Mangold, N., Peulvast, J.P., 2002. Science 295, 110–113; Christensen, P.R., 2003. Nature 422, 45–48; Treiman, A.H., 2003. J. Geophys. Res. 108]. At higher obliquity than the present epoch, near-surface ground ice should be present globally [Mellon, M.T., Jakosky, B.M., 1995. J. Geophys. Res. 100 (E6), 11781–11799], populated by condensation of atmospheric water vapour in the top few metres of the regolith, or emplaced as dusty ice sheets reaching down towards the equator. The latitudinal restriction of these gullies to regions poleward of ±30° appears to argue against a thaw component to their formation—since ground ice is present and stable at all latitudes at high obliquity, the current (low) obliquity regime should result in ground ice thaw at low latitudes, where insolation and daytime temperatures are currently greatest, and this is not observed. A previously undescribed meltwater sequence in the Cerberus plains, at 20° N/187° E, shows that comparable, but much more continuous, and mappable melting and surface runoff have occurred in the geologically recent past at near-equatorial latitudes on Mars. Polygonal ground in the Cerberus plains is seen by the Mars Global Surveyor Mars Orbiter Camera (MOC) to suffer sequential, regional-scale volatile-loss consistent with thaw of near-surface ground ice under periglacial conditions. This degradation is continuously sampled by a single MOC strip, showing an icy landscape undergoing thaw modification and collapse, and may form the first evidence of equatorial wet-based glaciation during late Amazonian time, with indications of melting within the last million years. The dissolution and re-formation of polygonal ground links this landform to freeze–thaw processes, providing the conclusion to a question that has been the subject of debate for three decades—whether Mars' polygonal grounds require ice to form—and a consistent explanation for the fate of the water that carved the great outflow channels, much of which may still reside as ground ice in the regolith. This thaw occurs in the Cerberus Formation; deposits that are considered to be magmatic in origin, and the type formation for late-stage, “plains-style” volcanism on Mars [Keszthelyi, L., McEwen, A.S., Thordarson T., 2000. J. Geophys. Res. 105, 15027–15049]. By superposing large numbers of small impact craters, polygonal ground in the Cerberus plains sustains previous suggestions of a non-magmatic origin for this and other landforms in the region [Page, D.P., Murray, J.B., 2006. Icarus 183, 46–54]. Together, these periglacial landforms document evidence of climate change much younger than is currently recognised by crater counts, with important implications for age constraints on young surfaces and absolute age determinations by this method. It is tentatively suggested that this melting may be occurring today, with a striking correspondence between permafrost thaw in the Cerberus plains, the high atmospheric methane flux currently observed over this region [Mumma, M.J., Novak, R.E., DiSanti, M.A., Bonev, B.P., Dello Russo, N., 2004. Bull. Am. Astron. Soc. 36, 1127; Krasnopolsky, V.A., Maillard, J.P., Owen, T.C., 2004. Icarus 172, 537–547; Formisano, V., Atreya, S., Encrenaz, T., Ignatiev, N., Giuranna, M., 2004. Science 306, 1758–1761], and the only latitude zone on Mars—equatorward of 30° N—where melting of ground ice is thought possible in the current climate [Haberle, R.M., McKay, C.P., Schaeffer, J., Cabrol, N.A., Grin, E.A., Zent, A.P., Quinn, R., 2001. J. Geophys. Res. 106 (E10), 23317–23326; Lobitz, B., Wood, B.L., Averner, M.M., McKay, C.P., 2001. Proc. Natl. Acad. Sci. 98, 2132–2137]. Low-latitude polygonal ground as transient, and hydrologically active over wide areas transforms our understanding of the recent climatic evolution of Mars, supporting models of atmospheric water-ice migration [Mischna, M., Richardson, M.I., Wilson, R.J., McCleese, D.J., 2003. J. Geophys. Res. 108 (E6). 5062], complex, volatile stratigraphies [Clifford, S.M., Parker, T.J., 2001. Icarus 154, 40–79], and hypothesised, geologically recent ‘ice ages’ [Head, J.W., Mustard, J.F., Kreslavsky, M.A., Milliken, R.E., Marchant, D.R., 2003. Nature 426, 797–802]. The temporal coincidence of glacial epochs on the Earth and Mars during the Quaternary and latest Amazonian would suggest a coupled system linking both [Sagan, C., Young, A.T., 1973. Nature 243, 459].

Stratigraphic architectures spotted in southern Melas Chasma, Valles Marineris, Mars

The distribution in space and time of liquid water on Mars is a haunting question because of its relevance to astrobiology and astroclimatology. To date, most orbital observations which attest to past fluvial and lacustrine activity on Mars have been dedicated to surficial landforms (i.e., drainage networks and depositional fans). Here we report an unprecedented identification of typical stratigraphic architectures made in Mars Global Surveyor Mars Orbiter Camera images of layered material in southern Melas Chasma. A particular set of strata is arranged in three depositional sequences bounded by stratigraphic unconformities. The sequences show spectacular, steeply-inclined clinoforms, and a broad channel-like depression. There are the same complex stratal patterns in Valles Marineris on Mars as there are in terrestrial deposits. Insights into these three-dimensional deposit geometries are used to tentatively isolate specific depositional processes and point to ancient subaqueous settings. Findings in southern Melas mark out a very attractive spot to which the search for ancient habitable environments on Mars could be directed.

Present-Day Impact Cratering Rate and Contemporary Gully Activity on Mars

The Mars Global Surveyor Mars Orbiter Camera has acquired data that establish the present-day impact cratering rate and document new deposits formed by downslope movement of material in mid-latitude gullies on Mars. Twenty impacts created craters 2 to 150 meters in diameter within an area of 21.5 x 10(6) square kilometers between May 1999 and March 2006. The values predicted by models that scale the lunar cratering rate to Mars are close to the observed rate, implying that surfaces devoid of craters are truly young and that as yet unrecognized processes of denudation must be operating. The new gully deposits, formed since August 1999, are light toned and exhibit attributes expected from emplacement aided by a fluid with the properties of liquid water: relatively long, extended, digitate distal and marginal branches, diversion around obstacles, and low relief. The observations suggest that liquid water flowed on the surface of Mars during the past decade.

Mars Orbiter Camera observations of Martian dust devils and their tracks (September 1997 to January 2006) and evaluation of theoretical vortex models

A multiyear, planet‐wide survey of Martian dust devils was conducted using observations from Mars Global Surveyor Mars Orbiter Camera, acquired through 21 January 2006. A total of 223,350 images were surveyed and 11,456 dust devils were seen in 0.4% of the images, 11.5% in the Southern and 88.5% in the Northern Hemisphere. Dust devils were observed at latitudes from 71.9°S to 62.2°N, over a range of surface albedos (Am∼0.11–0.22) and elevations from Hellas (−8750 m) to Arsia Mons (+17,250 m). The light‐ and dark‐toned streaks created by dust devils were observed from 80°S to 80°N and changed on timescales as short as 1 month. At mid‐to‐high latitudes, seasonal changes in streak patterns contribute to the seasonal “wave of darkening” observed telescopically from Earth. Dust devils were observed in all seasons in both hemispheres with the exception of Ls = 202.8°–281.5° in the north. Peak activity occurred during midsummer in each hemisphere. Five regions in Amazonis, Syria‐Claritas, Meridiani, and Gusev were monitored regularly. Amazonis had the largest dust devils and was the most active planet‐wide, with annual activity occurring from Ls∼8.5°–197°. Interannual variability resulted from dust storms and planet‐encircling dust hazes, which were observed to initiate and abate dust devil activity. There was no evidence suggesting dust devils cause or lead to initiation of dust storms. Model‐derived tangential wind speeds of large vortices were &gt;20 m s−1 at 20 m above the surface. Dust flux calculations suggest that dust devils are a contributor to the background dust opacity observed through northern spring and summer.

Dune migration and slip face advancement in the Rabe Crater dune field, Mars

Eight overlapping images of a dune slip face in Rabe Crater (35°E, 44°S) from the Mars Global Surveyor Mars Orbiter Camera show changes interpreted to be multiple grainflow events that would indicate present‐day sand saltation and dune migration. New occurrences of these features appear sporadically throughout late southern summer and early fall, and then no further changes occur throughout winter. By the following summer the pattern of old streaks had been almost completely covered by new dark streaks. Assuming that this activity is typical from year to year, migration rates are estimated to be on the order of 1–2 cm per martian year, produced by south to southeasterly winds that blow mostly during the southern spring and early summer. This slow migration rate is consistent with a present‐day sediment state that is either transport or availability limited.

Dust devil tracks and wind streaks in the North Polar Region of Mars: A study of the 2007 Phoenix Mars Lander Sites

The 65–72 latitude band of the North Polar Region of Mars, where the 2007 Phoenix Mars Lander will land, was studied using satellite images from the Mars Global Surveyor (MGS) Mars Orbiter Camera Narrow‐Angle (MOC‐NA) camera. Dust devil tracks (DDT) and wind streaks (WS) were observed and recorded as surface evidence for winds. No active dust devils (DDs) were observed. 162 MOC‐NA images, 10.3% of total images, contained DDT/WS. Phoenix landing Region C (295–315W) had the highest concentration of images containing DDT/WS per number of available images (20.9%); Region D (130–150W) had the lowest (3.5%). DDT and WS direction were recorded for Phoenix landing regions A (110–130W), B (240–260W), and C to infer local wind direction. Region A showed dominant northwest‐southeast DDT/WS, Region B showed dominant north‐south, east‐west and northeast‐southwest DDT/WS, and region C showed dominant west/northwest – east/southeast DDT/WS. Results indicate the 2007 Phoenix Lander has the highest probability of landing near DDT/WS in landing Region C. Based on DDT/WS linearity, we infer Phoenix would likely encounter directionally consistent background wind in any of the three regions.

Interannual variability of water ice clouds over major martian volcanoes observed by MOC

Using Mars Global Surveyor Mars Orbiter Camera daily global maps, cloud areas have been measured daily for water ice clouds associated with the topography of the major volcanoes Olympus Mons, Ascraeus Mons, Pavonis Mons, Arsia Mons, Elysium Mons, and Alba Patera. This study expands on that of Benson et al. [Benson, J.L., Bonev, B.P., James, P.B., Shan, K.J., Cantor, B.A., Caplinger, M.A., 2003. Icarus 165, 34–52] by continuing their cloud area measurements of the Tharsis volcanoes, Olympus Mons and Alba Patera for an additional martian year (August 2001–May 2003) and by also including Elysium Mons measurements from March 1999 through May 2003. The seasonal trends in cloud activity established by Benson et al. [Benson, J.L., Bonev, B.P., James, P.B., Shan, K.J., Cantor, B.A., Caplinger, M.A., 2003. Icarus 165, 34–52] for the five volcanoes studied earlier are corroborated here with an additional year of coverage. For volcanoes other than Arsia Mons, interannual variations that could be associated with the large 2001 planet encircling dust storm are minimal. At Arsia Mons, where cloud activity was continuous in the first two years, clouds disappeared totally for ∼85° of L S ( L S = 188 ° – 275 ° ) due to the dust storm. Elysium Mons cloud activity is similar to that of Olympus Mons, however the peak in cloud area is near L S = 130 ° rather than near L S = 100 ° .