Particle sieving and sorting under simulated martian conditions     

Luther W. Beegle  Gregory H. Peters  Rohit Bhartia  Luke Sollitt 《Icarus》2009,204(2):687-696

We report on sorting of small grained material under simulated martian conditions in order to better understand the nature of particle movement in the acquisition-to-analysis chain for future martian missions. We find that triboelectric charging when material is sieved is a major phenomenon that has to be understood and mitigation strategies explored in order to be able to successfully move particles under these types of conditions while minimizing cross sample talk. In different experimental set-ups, we have observed such phenomena as caking of the sieve, adhesion of particles to hardware, clodding of dry fines, and electrostatic repulsion. These phenomena occur when different experimental testing is performed with varied configurations and environmental conditions. Identifying these electrostatic effects can help us understand potential bias in the analytical instruments and to define the best operational protocols to collect samples on the surface of Mars. These experiments demonstrate the need for end-to-end system testing under the most realistic environmental conditions and platforms before mission configurations can be demonstrated before launch.  相似文献   

Ancient melting of mid-latitude snowpacks on Mars as a water source for gullies     

K.E. Williams  O.B. Toon  J.L. Heldmann  M.T. Mellon 《Icarus》2009,200(2):418-425

We hypothesize that during past epochs of high obliquity seasonal snowfields at mid-latitudes melted to produce springtime sediment-rich surface flows resulting in gully formation. Significant seasonal mid-latitude snowfall does not occur on Mars today. General Circulation Model (GCM) results, however, suggest that under past climate conditions there may have been centimeters of seasonal mid-latitude snowfall [Mischna, M.A., Richardson, M.I., Wilson, R.J., McCleese, D.J., 2003. J. Geophys. Res. Planets 108, doi:10.1029/2003JE002051. 5062]. Gully locations have been tabulated by several researchers (e.g. [Heldmann, J.L., Mellon, M.T., 2004. Icarus 168, 285–304; Heldmann, J.L., Carlsson, E., Johansson, H., Mellon, M.T., Toon, O.B., 2007. Icarus 188, 324–344; Malin, M.C., Edgett, K.S., 2000. Science 288, 2330–2335]) and found to correspond to mid-latitude bands. A natural question is whether the latitudinal bands where the gullies are located correspond to areas where the ancient snowfalls may have melted, producing runoff which may have incised gullies. In this study we model thin snowpacks with thicknesses similar to those predicted by [Mischna, M.A., Richardson, M.I., Wilson, R.J., McCleese, D.J., 2003. J. Geophys. Res. Planets 108, doi:10.1029/2003JE002051. 5062]. We model these snowpacks under past climate regimes in order to determine whether snowmelt runoff could have occurred, and whether significant amounts of warm soil (T>273 K) existed on both poleward and equatorward slopes in the regions where gullies exist. Both warm soil and water amounts are modeled because soil and water may have mixed to form a sediment-rich flow. We begin by applying the snowpack model of Williams et al. [Williams, K.E., Toon, O.B., Heldmann, J.E., Mellon, M., 2008. Icarus 196, 565–577] to past climate regimes characterized by obliquities of 35° (600 ka before present) and 45° (5.5 ma before present), and to all latitudes between 70° N and 70° S. We find that the regions containing significant snowmelt runoff correspond to the regions identified by Heldmann and Mellon [Heldmann, J.L., Mellon, M.T., 2004. Icarus 168, 285–304], Heldmann et al. [Heldmann, J.L., Carlsson, E., Johansson, H., Mellon, M.T., Toon, O.B., 2007. Icarus 188, 324–344] and Malin and Edgett [Malin, M.C., Edgett, K.S., 2000. Science 288, 2330–2335] as containing large numbers of gullies. We find that the snowmelt runoff (>1 mm, with equivalent rainfall rates of 0.25 mm/h) and warm soil (>1 cm depth) would have occurred on slopes within the gullied latitudinal bands. The snowfall amounts modeled are predicted to be seasonal [Mischna, M.A., Richardson, M.I., Wilson, R.J., McCleese, D.J., 2003. J. Geophys. Res. Planets 108, doi:10.1029/2003JE002051. 5062], and our modeling finds that under the previous climate regimes there would have been meltwater present on the slopes in question for brief periods of time, on the order of days, each year. Our model provides a simple explanation for the latitudinal distribution of the gullies, and also suggests that the gullies date to times when water migrated away from the present poles to the mid-latitudes.  相似文献   

The formation and evolution of youthful gullies on Mars: Gullies as the late-stage phase of Mars’ most recent ice age     

James L. Dickson  James W. Head 《Icarus》2009,204(1):63-86

Gullies are extremely young erosional/depositional systems on Mars that have been carved by an agent that was likely to have been comprised in part by liquid water [Malin, M.C., Edgett, K.S., 2000. Evidence for recent groundwater seepage and surface runoff on Mars. Science 288, 2330-2335; McEwen, A.S. et al., 2007. A closer look at water-related geologic activity on Mars. Science 317, 1706-1709]. The strong latitude and orientation dependencies that have been documented for gullies require (1) a volatile near the surface, and (2) that insolation is an important factor for forming gullies. These constraints have led to two categories of interpretations for the source of the volatiles: (1) liquid water at depth beneath the melting isotherm that erupts suddenly (“groundwater”), and (2) ice at the surface or within the uppermost layer of soil that melts during optimal insolation conditions (“surface/near-surface melting”). In this contribution we synthesize global, hemispheric, regional and local studies of gullies across Mars and outline the criteria that must be met by any successful explanation for the formation of gullies. We further document trends in both hemispheres that emphasize the importance of top-down melting of recent ice-rich deposits and the cold-trapping of atmospherically-derived H₂O frost/snow as important components in the formation of gullies. This provides context for the incorporation of high-resolution multi-spectral and hyper-spectral data from the Mars Reconnaissance Orbiter that show that (1) cold-trapping of seasonal H₂O frost occurs at the alcove/channel-level on contemporary Mars; (2) gullies are episodically active systems; (3) gullies preferentially form in the presence of deposits plausibly interpreted as remnants of the Late Amazonian emplacement of ice-rich material; and (4) gully channels frequently emanate from the crest of alcoves instead of the base, showing that alcove generation is not necessarily a product of undermining and collapse at these locations, a prediction of the groundwater model. We interpret these various lines of evidence to mean that the majority of gullies on Mars are explained by the episodic melting of atmospherically emplaced snow/ice under spin-axis/orbital conditions characteristic of the last several Myr.  相似文献   

A method to infer past surface mass balance and topography from internal layers in martian polar layered deposits     

Michelle R. Koutnik  Edwin D. Waddington 《Icarus》2009,204(2):458-470

Internal layers in ice masses can be detected with ice-penetrating radar. In a flowing ice mass, each horizon represents a past surface that has been subsequently buried by accumulation, and strained by ice flow. These layers retain information about relative spatial patterns of accumulation and ablation (mass balance). Internal layers are necessary to accurately infer mass-balance patterns because the ice-surface shape only weakly reflects spatial variations in mass balance. Additional rate-controlling information, such as the layer age, the ice temperature, or the ice-grain sizes and ice-crystal fabric, can be used to infer the absolute rate of mass balance. To infer mass balance from the shapes of internal layers, we solve an inverse problem. The solution to the inverse problem is the best set or sets of unknown boundary conditions or initial conditions that, when used in our calculation of ice-surface elevation and internal-layer shape, generate appropriate predictions of observations that are available. We also show that internal layers can be used to infer martian paleo-surface topography from a past era of ice flow, even though the topography may have been largely altered by subsequent erosion. We have successfully inferred accumulation rates and surface topography from internal layers in Antarctica. Using synthetic data, we demonstrate the ability of this method to solve the corresponding inverse problem to infer accumulation and ablation rates, as well as the surface topography, for martian ice. If past ice flow has affected the shapes of martian internal layers, this method is necessary to infer the spatial pattern and rate of mass balance.  相似文献   

Power law of dust devil diameters on Mars and Earth     

Ralph D. Lorenz 《Icarus》2009,203(2):683-684

Estimates from visual surveys of the frequency of dust devils, even at terrestrial localities known for their abundance, vary by some four orders of magnitude, making a quantitative hazard assessment difficult. Here I show (1) that new high-quality observations from Mars fit a power law size distribution, (2) that such a power law population can unify the discrepant terrestrial surveys, and (3) that the populations on the two planets appear similar.  相似文献   

Low-order dynamical behavior in the martian atmosphere: Diagnosis of general circulation model results     

Oscar Martínez-Alvarado  Irene M. Moroz  Peter L. Read  Stephen R. Lewis  Luca Montabone 《Icarus》2009,204(1):48-62

The hypothesis of a low dimensional martian climate attractor is investigated by the application of the proper orthogonal decomposition (POD) to a simulation of martian atmospheric circulation using the UK Mars general circulation model (UK-MGCM). In this article we focus on a time series of the interval between autumn and winter in the northern hemisphere, when baroclinic activity is intense. The POD is a statistical technique that allows the attribution of total energy (TE) to particular structures embedded in the UK-MGCM time-evolving circulation. These structures are called empirical orthogonal functions (EOFs). Ordering the EOFs according to their associated energy content, we were able to determine the necessary number to account for a chosen amount of atmospheric TE. We show that for Mars a large fraction of TE is explained by just a few EOFs (with 90% TE in 23 EOFs), which apparently support the initial hypothesis. We also show that the resulting EOFs represent classical types of atmospheric motion, such as thermal tides and transient waves. Thus, POD is shown to be an efficient method for the identification of different classes of atmospheric modes. It also provides insight into the non-linear interaction of these modes.  相似文献   

Towards self-consistent modeling of the martian dichotomy: The influence of one-ridge convection on crustal thickness distribution     

Tobias Keller  Paul J. Tackley 《Icarus》2009,202(2):429-443

In order to find an explanation for the origin of the martian crustal dichotomy, a number of recent papers have examined the effect of layered viscosity on the evolution of a degree-1 mantle convection, e.g. Roberts and Zhong [Roberts, J.H., Zhong, S., 2006. J. Geophys. Res. 111. E06013] and Yoshida and Kageyama [Yoshida, M., Kageyama, A., 2006. J. Geophys. Res. 111, doi:10.1029/2005JB003905. B03412]. It was found that a mid-mantle viscosity jump, combined with highly temperature- and depth-dependent rheology, are effective in developing a degree-1 convection within a short timescale. Such a layered viscosity profile could be justified by martian mineralogy. However, the effect of a degree-1 convective planform on the crustal thickness distribution has not yet been demonstrated. It is not obvious whether a thinner crust, due to sublithospheric erosion and crustal thinning, or a thicker crust, due to enhanced crustal production, would form above the hemisphere of mantle upwelling. Also, the general shape of the dichotomy, which is not strictly hemispherical, has not yet been fully investigated. Here we propose a model of the crustal patterns produced by numerical simulations of martian mantle convection, using the finite-volume multigrid code StagYY [Tackley, P.J., 2008. Phys. Earth Planet. Int. 107, 7-18, doi:10.1016/j.pepi.2008.08.005] A self-consistent treatment of melting, crustal formation and chemical differentiation has been added to models of three-dimensional thermal convection. This allows us to obtain global maps of the crustal thickness distribution as it evolves with time. The obtained results demonstrate that it is indeed possible to form a crustal dichotomy as a consequence of near degree-1 mantle convection early in Mars' history. We find that some of the observed patterns show intriguing first order similarities to the elliptical shape of the martian dichotomy. In all models, the region of thick crust is located over the region of mantle upwelling, which itself is a ridge-like structure spread over roughly one half of the planet, a planform we describe as “one-ridge convection.”  相似文献   

Effects of surface roughness and graybody emissivity on martian thermal infrared spectra     

Joshua L. Bandfield 《Icarus》2009,202(2):414-8420

Slopes are present in martian apparent surface emissivity observations collected by the Thermal Emission Spectrometer (TES) and the Thermal Emission Imaging System (THEMIS). These slopes are attributed to misrepresenting the surface temperature, either through incorrect assumptions about the maximum emissivity of surface materials or the presumption of a uniform surface temperature within the field of view. These incorrect assumptions leave distinct characteristics in the resulting apparent emissivity data that can be used to gain a better understanding of the surface properties. Surfaces with steep slopes typically have a variable surface temperatures within the field of view that cause distinct and highly variable slopes in apparent emissivity spectra based on the observing conditions. These properties are documented on the southwestern flank of Apollinaris Patera and can be reasonably approximated by modeled data. This spectral behavior is associated with extremely rough martian surfaces and includes surfaces south of Arsia Mons and near Warrego Valles that also appear to have high slopes in high resolution images. Surfaces with low maximum values of emissivity have apparent emissivity spectra with more consistent spectral slopes that do not vary greatly based on observing conditions. This spectral surface type is documented in Terra Serenum and is consistent with associated high resolution images that do not indicate the presence of a surface significantly rougher that the surrounding terrain.  相似文献   

The rate of granule ripple movement on Earth and Mars   总被引：1，自引：0，他引：1  

James R. Zimbelman  Rossman P. Irwin III  Fred Bunch  Scott Stevens 《Icarus》2009,203(1):71-10

The rate of movement for 3- and 10-cm-high granule ripples was documented in September of 2006 at Great Sand Dunes National Park and Preserve during a particularly strong wind event. Impact creep induced by saltating sand caused ∼24 granules min⁻¹ to cross each cm of crest length during wind that averaged ∼9 m s⁻¹ (at a height well above 1 m), which is substantially larger than the threshold for saltation of sand. Extension of this documented granule movement rate to Mars suggests that a 25-cm-high granule ripple should require from hundreds to thousands of Earth-years to move 1 cm under present atmospheric conditions.  相似文献   

Concentric crater fill in Utopia Planitia: History and interaction between glacial “brain terrain” and periglacial mantle processes     

Joseph S. Levy  David R. Marchant 《Icarus》2009,202(2):462-216

At martian mid-to-high latitudes, the surfaces of potentially ice-rich features, including concentric crater fill, lobate debris aprons, and lineated valley fill, typically display a complex texture known as “brain terrain,” due to its resemblance to the complex patterns on brain surfaces. In order to determine the structure and developmental history of concentric crater fill and overlying latitude-dependent mantle (LDM) material, “brain terrain” and polygonally-patterned LDM surfaces are analyzed using HiRISE images from four craters in Utopia Planitia containing concentric crater fill. “Brain terrain” and mantle surface textures are classified based on morphological characteristics: (1) closed-cell “brain terrain,” (2) open-cell “brain terrain,” (3) high-center mantle polygons, and (4) low-center mantle polygons. A combined glacial and thermal-contraction cracking model is proposed for the formation and modification of the “brain terrain” texture of concentric crater fill. A similar model, related to thermal contraction cracking and differential sublimation of underlying ice, is proposed for the formation and development of polygonally patterned mantle material. Both models require atmospheric deposition of ice, likely during periods of high obliquity, but do not require wet active layer processes. Crater dating of “brain terrain” and mantled surfaces suggests a transition at martian mid-latitudes from peak “glacial” conditions occurring within the past ∼10-100 My to a quiescent period followed by a cold-desert “periglacial” period during the past ∼1-2 My.  相似文献