Wind erosion of layered sediments on Mars: The role of terrain

For submission to ROSES - Solar System Workings 2014 (NNH14ZDA001N-SSW)

1. Table of contents............................................................................................................0

2. Scientific/Technical/Management................................................................................1

2.1 Executive Summary...............................................................................................1

2.2 Goals of the Proposed Study.................................................................................1

2.3 Relevance to NASA Strategic Goals.....................................................................1

2.4 Scientific Background............................................................................................1

2.4.1. Wind Erosion on Mars..................................................................................3

2.4.2. Slope winds...................................................................................................3

2.4.3. Growth and form of sedimentary mounds....................................................4

2.5 Technical Approach and Methodology................................................................5

2.5.1. Application of the Mars Regional Atmospheric Modeling System..............5

2.5.2. Numerical experiments with idealized craters and canyons.........................6

2.5.3. Consideration of the effect of sedimentary infill (sedimentary mounds).....8

2.5.4. Simulation of slope-eroding winds for geologically realistic terrain............9

2.5.5. Incorporation of slope winds into landscape evolution model...................10

2.5.6. Assumptions and caveats............................................................................11

2.6 Impact of Proposed Work...................................................................................11

2.7 Relevance of Proposed Work..............................................................................12

2.8 Work Plan ............................................................................................................12

2.8.1. Work plan....................................................................................................12

2.8.2. Planned calculations and the parameters explored.....................................13

3. References.....................................................................................................................15

4. Biographical sketches..................................................................................................205. Current and Pending Support....................................................................................256. Statements of Commitment.........................................................................................267. Budget Justification.....................................................................................................27 6.1.1. Personnel and Work Efforts 6.1.2. Facilities and Equipment 6.2 Budget Details8. Subcontract to the SETI Institute ............................................................................28

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2. Scientific/Technical/Management:

2.1 Executive SummarySlope-enhanced wind erosion is the dominant process shaping layered sediments on Mars today, and the sedimentary rock record may be predominantly a record of aeolian processes. Ubiquitous downslope-oriented yardangs, a paucity of small craters on steep slopes, and the existence of moats girdling mounds that have layers exposed around their perimeters all suggest that wind erosion defines the present-day outcrop topography of layered sediments such as Gale crater’s mound (Mt. Sharp / Aeolis Mons), low-latitude alluvial-fan deposits, and the Valles Marineris interior layered deposits. Despite the importance of aeolian denudation on Mars, there is currently no physical model of the effect of long-term wind erosion on Martian landscape evolution (and vice versa). We propose to fill this gap by utilizing mesoscale models to parameterize the effect of slope winds on Martian wind erosion, and incorporating this understanding into a landscape evolution model capable of probing atmosphere-landscape coupling over longer timescales. We shall thus obtain:- 1) a parameterization of the effect of terrain on wind erosion at the scale of sedimentary mounds and the craters and canyons that host them; 2) quantitative constraints on the processes and pattern of terrain-influenced near-surface winds on Mars at atmospheric pressures 6-384 mbar; 3) predictions of how evolving, erodible topography couples to the terrain-influenced erosive windfield. Therefore, the proposed work will improve our understanding of atmosphere-surface interaction on both modern and ancient Mars.

2.2 Goal of the proposed studyThe primary objective of the proposed work is to constrain the role of slope winds in shaping sedimentary accumulations using long-term erosion potential inferred from the windfield output of mesoscale models. This will involve the following steps:

Step 1. Mesoscale numerical experiments with idealized crater/canyon topography.Step 2. Additional mesoscale runs with sedimentary infill (sediment mounds and sheets).Step 3. Compare model output to geological data in complex terrain.Step 4. Run landscape evolution model incorporating parameterization of mesoscale results.

We hypothesize that slope-wind enhanced erosion can explain the nearly-universal (though poorly understood) “moat-and-mound” topography of layered-sediment-hosting craters and canyons.

2.4 Scientific background

2.3.1. Wind erosion on Mars: Wind erosion occurs when surface wind stresses are high enough for saltation, allowing saltating sand-sized particles to strike erodible surfaces [Greeley & Iverson, 1982; Anderson, 1986; Kok et al., 2012]. On Mars, saltating sand sized particles are in active motion [e.g., Bourke et al., 2008; Chojnacki et al., 2011; Silvestro et al., 2011], at rates that predict aeolian erosion of bedrock at 10-50 μm/yr [Bridges et al., 2012a]. Within the last ~0.1 Ma, wind has mobilized particles ranging from dust aggregates to hematite granules [Sullivan et al., 2008, Golombek et al., 2010]. Aeolian abrasion of sedimentary rock has occurred within the last roughly 1-10 Ka [Golombek et al., 2010; Figure

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1] and at Yellowknife Bay in Gale crater, rapid retreat of a >2m-high scarp due to aeolian erosion ~80 Ma is required by coincident 3He, 36Ar, and 21Ne exposure ages [Farley et al., 2014]. These recent findings make a compelling case for aeolian erosion on modern Mars, and cap four decades of research into Martian aeolian bedforms, saltation and aeolian erosion [e.g., Sagan, 1973; Iverson et al., 1975; Ward, 1979; Thomson et al., 2008; de Silva et al. 2010; Montgomery et al., 2012; and many others]. Intriguingly, the observed locations of sand transport cannot be reproduced by General Circulation Models (GCMs), which suggests that mesoscale winds (not the regional-to-global winds resolved by GCMs) are responsible for saltation [Bridges et al., 2013; Chojnacki et al., 2011]. The mesoscale circulation within craters and canyons is dominated by slope winds as a consequence of Mars’ thin atmosphere [e.g. Rafkin & Michaels, 2003; Spiga & Forget, 2009, Vasavada et al., 2012; Tyler & Barnes, 2013, Pla-García et al., 2014]. These high-relief regions are where most sulfate-bearing sedimentary rocks are found. The sedimentary mounds of the Valles Marineris, Gale, and the Medusae Fossae Formation, as well as layered dust aggregates on the flanks of large volcanoes, show downslope-oriented yardangs and grooves, a paucity of small craters, and (frequently) ferric-oxide lags - indicating geologically recent or ongoing wind erosion [Roach et al., 2010]. With erosion rates outpacing cratering for many sedimentary-rock outcrops [Malin et al., 2007], and geologic and model estimates agreeing on the potential for many km of cumulative erosion [Armstrong & Leovy, 2005], wind erosion is the most important process changing mesoscale topography on Mars today and has been a first-order control on landscape evolution in sedimentary terrain.

Aeolian erosion was also important earlier in Mars history. Aeolian materials likely represent a volumetrically significant component of the ancient sedimentary rock record [Grotzinger & Milliken, 2012]; most of the observed sedimentary bedforms at the Opportunity and Spirit landing sites are sand dune foresets [Hayes et al., 2011]; and many aeolian materials exist within the strata of the Gale mound [Anderson & Bell, 2010, Milliken et al. 2014, Kocurek & Ewing, 2012]. Aeolian deflation/erosion surfaces within the sedimentary record of Mars are suggested by laterally extensive unconformities with a smooth, non-horizontal expression [e.g., Malin & Edgett, 2000; Kerber & Head, 2010; Holt et al., 2010; Okubo, 2010; Fueten et al., 2008; Zabrusky et al., 2012; Zimbelman & Scheidt, 2012, Kite et al., submitted]. Therefore, geologically recent wind erosion links present-day aeolian activity to the shaping of

Figure 1. Evidence for slope wind erosion of layered sediments on Mars, at a variety of length scales. Left panel: blueberry lag from aeolian erosion surrounds 30cm-diameter block ejected from ~1-10 Ka crater [Golombek et al. 2010]; center panel, yardangs from West Candor Chasma (MOC NA M1301494; 2km across). Right panel: Mesoscale topographic undulations within the Candor canyon sediments (image is ~600km across).

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sedimentary archives extending towards Mars’ more-habitable early period, and may also be a modern analog for a process that has operated (to varying degrees) throughout Mars history.

2.4.2. Slope windsThe early loss of much of Mars’ atmosphere has made Mars a natural laboratory for studying the coupling between terrain and slope-wind erosion. With an atmospheric pressure close to the triple point of water, erosion by liquid water is no longer significant at the mesoscale, so steep basaltic slopes with many km of relief have persisted for Gyr (sedimentary deposits on Mars are much less resistant to abrasion than unweathered basalt; Herkenhoff et al.

2008). Because of the thin atmosphere and weak greenhouse effect, the surface is close to radiative equilibrium. The combination of high relief, a 130K low-latitude diurnal temperature cycle, and an atmospheric lapse rate that is smaller than Earth’s (and very poorly coupled to surface temperature) leads to strong diurnally-reversing slope winds [e.g. Kass et al., 2003]. Slope winds are particularly strong within the equatorial craters and canyons that host sedimentary rock mounds, where coriolis effects are weak and relief is particularly high. The thin atmosphere also allows for topographic control of the large-scale circulation [e.g. Zalucha et al., 2010], and slope effects drive regional winds over even very gentle slopes [e.g., Savijarvi & Siili, 1993].

Slope wind studies on Earth have validated semi-analytic treatments of katabatic winds (and drainage flows) that make idealized assumptions about entrainment and topography, but also shown their limitations, especially in areas of complex topography where strongly nonlinear effects dominate [e.g. Ellison & Turner, 1959; Manins & Sawford, 1979; Parish & Bromwich,

1987; Horst & Doran, 1986; Papadopoulos et al., 1997; Shapiro & Federovich, 2007, Trachte et al., 2010]. Semi-analytic models do not consider long-term changes in atmospheric pressure, inertial-runout effects, or terrain-landscape feedbacks. Small-scale topography-windfield coupling produces sand dunes, but mesoscale topography-windfield coupling is not understood in part because slope wind erosion of bedrock is uncommon on Earth [Rohrmann et al., 2013]. There is no simple existing parameterization for slope winds in realistic terrain.

The proposed work will bring together the existing knowledge base on wind erosion and on slope winds.

[SHOW JUVENTAE] Figure 2. Example of MRAMS output, showing atmospheric response in a region of complex topography (Kite et al., 2011a.)

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Figure 3 . Examples of layered sediments within mounds, surrounded by moats. (Left) At the 30km-diameter Opportunity rover field site, a thin tongue of sedimentary sulfates is three-quarters encircled by a moat. (Center) Radar cross section of Korolev Crater’s ice mound. (Right) Gale Crater. Credits: UMSF; ASI/SHARAD/Jack Holt; DLR/ESA.

2.4.3. Growth and form of sedimentary moundsMost of Mars’ sulfate-bearing sedimentary rocks are in the form of intra-crater or intra-canyon mounded deposits surrounded by moats. Moats are typically 10-20 km wide. Most researchers agree that wind erosion is responsible for shaping the moats and mounds [e.g. Murchie et al., 2009; Okubo, 2010; Andrews-Hanna, 2012; Kite et al., 2013b]. However, identifying the physical mechanism(s) that account for the development of sedimentary mounds and moats has been challenging because physically motivated parameterizations of the coupling between terrain and slope-wind erosion are lacking. It is this gap that the proposed work will fill. Several processes may contribute to slope-wind erosion:- (i) breakdown of sedimentary layers to wind-transportable fragments by processes associated with chemical transformations, such as weathering and/or volume changes associated with hydration state changes [e.g., Chipera & Vaniman, 2007]; (ii) physical degradation of

hillslopes by mass wasting, followed by aeolian removal of talus to maintain steep slopes and allow continued mass wasting; (iii) aeolian erosion of weakly salt-cemented sediments [Shao, 2000, Ch. 9]; (iv) aeolian abrasion of bedrock [Wang et al., 2011]. These processes range from transport-limited to detachment-limited, and predict correspondingly different shear-stress dependencies, threshholds for erosion, and mesoscale mound morphologies (Fig. XX).

Figure XX. Here will go a figure showing the different mound morphologies for different erosion rules.

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2.5 Proposed workOur approach exploits the decoupling of timescales between the brief strong gusts that are responsible for wind erosion, and the millions of years needed to substantially reshape the topography that steers the gusts. Therefore, we run mesoscale models with fixed topography, and use the output from a grid of mesoscale models to obtain a parameterization for incorporation into a landscape evolution model.

2.5.1. Description of the MRAMS (Mars Regional Atmospheric Modeling System).

We will use MRAMS, which is derived from the terrestrial RAMS code [Pielke et al. 1992] and has been adapted to Mars problems by Co-I Michaels and Collaborator Rafkin.  MRAMS was used for entry, descent and landing simulations for the Mars Exploration Rovers, Mars Phoenix, and Mars Science Laboratory [Rafkin et al. 2001; Michaels and Rafkin, 2008, Vasavada et al. 2012] and has also been used in LES mode to study aeolian processes including dust lifting [Fenton & Michaels, 2010]. Because of our focus on dynamics, the aerosol microphysics capabilities of MRAMS [e.g. Michaels 2006] will not be used:- instead, dust will be specified using a simple, fixed Conrath-nu profile (both dust storm and low-dust conditions will be considered), and water ice will be zeroed out, leading to a several-fold improvement in computational speed. Water vapor will be included only as a passive, noncondensible tracer, and initial and boundary conditions will be chosen self-consistently so that water vapor is never saturated. Consistent with theory for saltation on Mars [Kok et al., 2012], we assume that the density of saltating grains at a given time is insufficient to modify the wind profile within the surface layer.

Vertical resolution will be varied from 2.3 km at the top of the model to 3 m near the ground. Horizontal resolution will be adjusted to be the lesser of 3km or 1.5% of the width of the feature being simulated (crater or canyon). Output will be sampled every 60s in order to capture short-lived wind events. Calculations shall be carried out on the Midway cluster at U. Chicago. CPU requirements are set by the longest allowable timestep, which decreases with increasing simulated relief. From experience gained during a prior collaboration [Kite et al. 2011a, 2011b], we expect to spend ≤1 CPU month for idealized-terrain runs and ~2 CPU months for Valles Marineris simulations. Midway’s capabilities easily satisfy all our CPU and storage requirements.

Periodic boundary conditions in the horizontal dimensions will be employed, and an absorbing (“sponge”) upper boundary condition will be used. MRAMS shall be initialized with no motion and spun up until output from successive sols has converged; we expect this will require 2-4 simulated sols (longer for high-pressure runs). Other initial and boundary conditions will be varied, as specified below.

2.5.2. Step 1: Numerical experiments with idealized craters and canyons.Initially we will use idealized topography to simulate a diurnal cycle of slope winds. We hypothesize that the strongest winds occur near the bottom of the slope and in a ‘runout zone’ on the floor. The existence and width of this runout zone is crucial because it can enhance erosion and/or prevent accumulation, defining the observed moats.

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Figure 4. South-to-north vertical cross-section across Valles Marineris as simulated by MRAMS. Wind speed is shaded, temperature (K) is contoured. Upslope winds are noted along the canyon walls, and compensating subsidence is evidence in the center of the canyon. This compensating flow is poorly represented in semi-analytic models.

Input to the model will be as follows. Idealized topography for craters will be axisymmetric, using a typical depth:diameter ratio for mound-hosting craters on Mars (3 km depth, a 1km high rim, 20° rim and wall slope and a flat floor). There shall be a central peak summiting at the elevation of surrounding plains and with 20° slopes. Idealized topography for canyons will have prismatic symmetry: a 5km deep trough with no rim, 20° wall slopes and a flat floor. As appropriate for equatorial layered sediments, there will be no Coriolis force in the horizontal plane. Diurnal solar forcing will be constant and equinoctial (0.50 sols of sunlight) at Mars’ mean distance from the Sun, but local time will be tracked in an E-W sense in order to permit a diurnal thermal tide. The surrounding terrain will be flat, and the distance to the edge of the model domain shall be no less than 3000 km including lower-resolution nest grids. Thermal inertia retrievals near strong terrain are unreliable because of slope winds [Spiga et al., 2011]; we will adopt a uniform thermal inertia of 230 J m -2 K-1 s-1/2 and uniform albedo 0.23 (corresponding to thermophysical class C of Putzig et al., 2005). We assume uniform aerodynamic roughness 10-2 m, intermediate between roughnesses calculated for the MPF and PHX sites [Hébrard et al., 2012]. The atmosphere shall be initialized with a Meridiani-like vertical thermal profile.

Output will consist of shear velocity (magnitude and direction) at all surface points. From this we will derive maps of the mean, maximum and skewness (gustiness) of the windfield. We will convolve this with existing theories for sediment transport and wind erosion to calculate the gross bedform-normal transport and erosion potential at each point as a function of the cohesion/abrasion susceptibility of the substrate. The theories employed [Shao, 2001; Kok, 2012] will be appropriate for (i) transport limited sand, (ii) soil, (iii) weakly salt-cemented soil, (iv) detachment-limited bedrock abrasion. [Specifically, ….. ] We will measure the runout distance/correlation length scale for each model run.

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Figure 5. Rationale for length scales chosen for the idealized model runs. Blue dots correspond to nonpolar craters, red squares correspond to canyons, and green dots correspond to polar ice mounds. Vertical dashed lines correspond to model runs discussed in the text. Gray vertical lines show range of uncertainty in largest-mound width Valles Marineris/circum-Chryse mounds. Blue dot to left of “G” corresponds to Gale Crater. Width is defined as polygon area divided by the longest straight-line length that can be contained within that polygon. Normalized mound width does not keep pace with increasing container size, a trend that we will investigate using the results from Step 2.

The following parameters will be varied: First, we will carry out a set of runs varying width:- craters 20 km, 40 km, 80 km

(reference crater), 160 km, and 320 km diameter; and canyons 60 km, 120 km (reference canyon) and 240 km wide. These dimensions are of particular interest, based on our survey of mound-hosting craters and canyons on Mars (Figure 5). We will also carry out runs for 2 km crater diameter and 10km canyon (=valley) width, to look for interesting behavior at small length scale as observed in Meteor Crater, Arizona [Kiefer & Zhong, 2011]. Mars has lost CO2

over time, so we will vary atmospheric for our reference crater and reference canyon. From the reference case at 6 mbar, we will model 24, 96 and finally 384 mbar (Earthlike atmospheric density). This will also allow us to investigate the transition from Earthlike to Marslike katabatic winds, and to testing the prediction from GCMs that a thick early atmosphere would have enabled higher rates of wind erosion [Armstrong & Leovy, 2005]. Because of the longer thermal time constant of denser atmospheres, these runs will require proportionately longer spin-up time. We will investigate the effect of wall slope by carrying out runs at 5° and 30° slope for the reference cases. To determine the effect of dust on slope winds, we will carry out 1 run for the reference crater case under high-dust (τIR ~3) conditions, maintaining a Conrath-ν profile in the vertical. To investigate katabatic-anabatic asymmetries, we will carry out one crater run with reversed topography. This geologically unrealistic run will allow us to separate the effect of divergent flow (daytime upslope) from day-night asymmetry for the crater case. In order to link to the general circulation (and the effects of changing orbital forcing), we will test the effect of a synoptic background wind field of 5 m/s imposed at the boundary (perpendicular to the canyon), and seperately to a Coriolis force (f-plane approximation) appropriate for 50° latitude (50° is the approximate latitude of Galle and Spallanzani, which contain the highest-latitude sedimentary mounds on Mars). Finally, we will carry out one run at 0.75x present-day solar luminosity. A significant advantage of using smooth, idealized topography is that it allows for a larger timestep, and so more runs for the same computational expense. In total, we propose 28 runs for Step 1.

2.5.3. Step 2: Consideration of the effect of sedimentary infill (sheets and mounds). We hypothesize that the presence of a sedimentary mound intensifies wind erosion potential within the crater/canyon.

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In step 2 we introduce sedimentary infill to the containers (craters/canyons) modeled in step 1. We will consider both sedimentary sheets (filling the crater to uniform elevation; e.g. Asimov crater), and sedimentary mounds. Mars sedimentary rock mounds tend to steepen near their toe, so we will adopt initial mound profiles of the form z ∝ sqrt(1 - x2), where z is elevation and x is distance from the center of symmetry of the container. Output will be the same as for the previous runs. In total, we will carry out XX runs in step 2. For each of the runs in step 1 (except the reversed-topography case), we will introduce infill of (half the height for sheet) and (full height and typical moat width for mound). Next, we specify a “reference” crater and a “reference” canyon. For these two “reference” container geometries, we will change infill thickness (X runs; <parameters>), infill width, wall slope, and container width. Additional runs will include:

Stepwise erosion of nearly-filled container. We will initialize the “reference” crater and canyon. We will define an erosion rate map using the with a threshold u* of 90% of the maximum wind speed experienced anywhere in the model domain during the first run using a cohesive-soil wind erosion law for the sedimentary infill and zero erosion elsewhere. The erosion rate map will be used to construct an eroded topography differing from the previous cycle by at most 1/5 of the original thickness of sedimentary infill, and the mesoscale model rerun on this altered topography. We will repeat this cycle 7 times for each container type.

As in Task 1, we will carry out a run with synoptic u = 5 m/s. We will also investigate asymmetric mound placement (1 simulation).

Icelike material properties. Taking account of reports of slope-wind erosion being important in the north polar ice

mounds (Brothers et al. 2013, Brothers & Holt 2013), we will carry out 1 crater simulation with TI = 2000 for the mound.

Corrugated sheet: In these experiments we will corrugate the entire landscape (inside and outside the canyon) with small and large amplitude topographic oscillations oriented perpendicular to the canyon long axis. We will vary both amplitude and wavelength. The goal here is to determine if there is a preferred wavelength for slope-wind erosion on Mars that might correspond to the observed mode in moat width (15-20km).

Central peak test: Many mound-hosting craters on Mars (including Gale) have central peaks. To quantify the influence of these peaks on the erosion of the whole crater, we will , and difference the

By regressing results from Tasks 1 and 2, we will determine the explanatory power of the following topographic parameters in explaining mesoscale patterns of maximum shear stress

Diagram of stepwise erosion

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across high-relief Martian landscapes: (a) local slope, (b) drainage area, (c) vertical distance and (d) horizontal distance from furthest ridge, (e) vertical and (f) horizontal distance from nearest ridge, (g) potential energy in drainage area assuming uniform thickness of drainage flow, (h) all of the above criteria but with inverted topography (for upslope winds), and additional parameters, both jointly and separately. We will then use these results together with an information criterion to select a parameterization with an appropriate number of independent variables (some of the variables listed are not independent). Finally, we will compare the results to predictions from hydraulic (semi-analytic) theory, and analyze the residuals. Alongside this empirical approach (essentially multivariate regression), we will attempt to develop a physical theory to account for the numerical output.

2.5.4. Step 3: Simulation of slope-eroding winds for geologically realistic terrain.For layered sediments in Candor Chasma, we hypothesize that the strongest wind stresses occur in terrain that has undergone the highest rates of geologically recent erosion.

The floor of Candor Chasma is a sedimentary outcrop with very few impact craters, indicating high rates of erosion [Malin et al., 2007]. These high rates of erosion of sedimentary rock make Candor Chasma a suitable site to compare our wind/erosion models to geologic constraints on resurfacing. We will simulate winds at Candor Chasma using 4-5 nested grids forced at the outermost (hemispheric) nest by the NASA Ames Mars GCM. To constrain long-term wind erosion, we require four-season 24-hour output, climatological dust for each season, and no water cycle. Mesoscale output generated for mission support purposes does not satisfy these criteria. There is no evidence for strong control of orbital forcing on synoptic equatorial winds over the last 5 Mya, which is sufficient for determining the deflation rate recorded by the relative density of the small craters. (NEEDS PRELIMINARY) We will also calculate predicted yardang orientations (from km-scale shear stress vectors) [Sefton-Nash et al. 2014], pattern of erosion at mesoscale (10s-100s km), and rates of erosion. We will employ the full wind speed history to sedimentary transport and erosion for the detachment limited case [e.g., Wang et al., 2011], making the simplifying approximation dz/dt ≈ ke (u* – u*c)α

with α = 3 or 4 [Kok et al., 2012]. This full-history calculation will allow us to determine whether nighttime winds, daytime winds, or both are important for wind erosion, and also to determine whether erosion rate can be approximated as a function of the maximum wind speed only. We will also carry out 1 control experiment at perihelion season using zero wind at the outermost model boundaries in order to isolate the contribution of the general circulation to wind erosion. (Total: 5 experiments for Task 3).

Each of these predictions is testable using existing CTX and HiRISE images of West Candor Chasma that are available in the PDS. Yardang orientations will be plotted where visible and the residuals relative to prediction calculated on a ½ degree grid across the chasm [Sefton-Nash et al., 2014]. For the part of the model domain corresponding to sedimentary rock, we will convert from relative to absolute erosion rates using the mechanical properties of kieserite and epsomite that have recently been measured [Grindrod et al., 2010] to set abrasion susceptibility [ENOUGH? NEED A CLOSURE. SAY]. When erosion rates are high, small-crater frequency is inversely proportional to crater-obliteration rate [e.g., Smith et al., 2008; Kite et al., 2013x]. Crater size-frequency distributions will be collated (for sedimentary rock outcrops only, and excluding areas of obvious mass wasting and landslides) using a CTX

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basemap and available HiRISE. The crater density in Candor Chasma is low, so we will bin craters in order of the predicted erosion rate at that crater’s location which will allow us to compare the trend and magnitude of aeolian erosion appropriately. Extremely resistant (caprock) surfaces will be excluded. Our approach to obtaining crater-obliteration rates from crater counts will use Bayesian fitting (Kite et al. 2013x). Bayesian fitting has the advantage that size bins containing a small number of craters can contribute to the fit, whereas they are usually discarded when sqrt(N) error bars are incorporated (Figure YY). Published crater-counts for Mars layered sediments confirm that sufficient craters are present for analysis, and show the expected shallowing of the crater-size frequency curve expected for wind erosion (Sefton-Nash et al. 2014, Kite et al. 2013x). Because converting crater size-frequency curves to an erosion rate requires the assumption that crater obliteration is due to surface lowering, rather than crater infilling, we consider this only a relative (rather than absolute) estimate of erosion rate.

Finally, we will compare models to data to assess the performance of our model. This requires setting a threshold wind speed for wind erosion. We will assume that the threshold wind speed for erosion is the (atmospheric-pressure-dependent) threshold for saltation, with erosion above the threshold depending on the kinetic energy .

2.5.5. Step 4: Incorporation of slope winds into landscape evolution model.We hypothesize that slope wind/landscape feedbacks played a significant role in the current shape of moats and mounds on Mars, including Gale Crater’s Mt. Sharp / Aeolis Mons.

In this final step we will incorporate the parameterization linking topography to wind erosion as an erosion rule in a landscape evolution model.Landscape evolution models trade decreased detail for the ability to model processes over geological time [Howard 2007, Ferrier et al., 2013, Whipple & Tucker, 1999]. We will adapt our computationally inexpensive landscape evolution model (Kite et al., 2013b) to implement

Figure 6. Preliminary work using landscape evolution model, showing simulated sedimentary mound growth and form for one example of a hypothetical idealized atmosphere-topography feedback (from Kite et al. 2013b). Colored lines correspond to snapshots of the mound surface equally spaced in time (blue being early and red being late). Black line corresponds to the initial nonerodible “container” topography. Topographic change is the balance of an atmospheric source term and wind erosion. In this hypothetical idealized case, the atmospheric source term is uniform in space and constant in time [e.g., Michalski & Niles, 2012] and the stratigraphy and geomorphology therefore results solely from slope-wind/terrain coupling, which is parameterized using an exponential kernel. See Kite et al. [2013b] for details of the coupling

Figure YY. Here we show preliminary work getting an erosion rate out of Sefton-Nash et al. 2014.

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the erosion rule obtained from. The model currently simulates landscape evolution in one horizontal dimension (radius or width) (Figure 6); we will extend this to two dimensions in our proposed work.

Following incorporation of the erosion rule obtained from the mesoscale runs, we will carry out parameter sweeps in the landscape evolution model. Because of the minimal computational cost of the landscape evolution model, we can carry out a large number of parameter sweeps. These shall include:- (i) nonerodible container initially overfilled with erodible material; (ii) nonerodible container initially half-filled with erodible material; (iii) coupled growth and wind erosion using uniform deposition. We shall also explore (iv) competing aeolian and fluvial processes (using Howard, 2007, for the fluvial processes; the marssim code is open-sourced at http://csdms.colorado.edu/). . Each of these parameter sweeps will consist of a wide range of crater and canyon dimensions, synoptic wind speeds, and wall slope angles. In each case, we will remove material from the landscape-evolution model domain as it is detached from the substrate, consistent with the small volumes of loose material adjacent to sedimentary-rock mounds on Mars today [e.g. Anderson & Bell, 2010].

The landscape evolution model will allow us to leverage the relatively small ensemble (~102

runs) of mesoscale models to explore a much wider range of parameter space. Thus we can determine if moats and moats are generic outcomes of slope wind erosion on Mars (supporting our hypothesis) or alternatively if special circumstances are required for moats and mounds to form from slope winds (disfavoring our hypothesis).

This model will allow study of 2-way mesoscale atmosphere geomorphology feedbacks on Mars. For example, the landscape evolution model will generate a large number of physically motivated predictions for the hypothesis that slope wind/terrain coupling played a significant role in the layer orientations and stratigraphy within sedimentary mounds on Mars (parameter sweep iii above), which can be tested from orbit (with HiRISE stereo DTMs), and by MSL as it ascends the Gale mound.

2.5.6 Assumptions and caveatsIt is worth emphasizing the limitations and assumptions of these modeling methods. First, this is a model-driven proposal whose primary goal is improved understanding of the patterns and processes of long-term wind erosion and landscape evolution. As with terrestrial landscape evolution research, global constraints on the absolute rates of landscape evolution will require calibration from cosmogenic isotopes, laboratory studies, and ultimately radiogenic dating, all of which are beyond the scope of this proposal. Second, we assume that armoring (lag formation) processes do not vary strongly across the model domain at the mesoscale. This means that the model is inapplicable to plains traversed by the Opportunity rover, where both slopes (<<1°) and long-term average erosion rates (~1 nm/yr) are small (Golombek et al. 2014) relative to the crater and canyon sites that we focus on (Smith et al. 2008). Finally, we track the energy available for erosion, but we do not track tools responsible for erosion in detail (there is no bookkeeping for abrading clasts). Because our ultimate goal is to develop a landscape evolution model, we assume that over long timescale tools are available.

2.6 Impact of proposed work

Figure 6. Preliminary work using landscape evolution model, showing simulated sedimentary mound growth and form for one example of a hypothetical idealized atmosphere-topography feedback (from Kite et al. 2013b). Colored lines correspond to snapshots of the mound surface equally spaced in time (blue being early and red being late). Black line corresponds to the initial nonerodible “container” topography. Topographic change is the balance of an atmospheric source term and wind erosion. In this hypothetical idealized case, the atmospheric source term is uniform in space and constant in time [e.g., Michalski & Niles, 2012] and the stratigraphy and geomorphology therefore results solely from slope-wind/terrain coupling, which is parameterized using an exponential kernel. See Kite et al. [2013b] for details of the coupling

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Current and Decadal-Survey-recommended missions. MSL is a mission to a layered sediment mound which is undergoing wind erosion which exposes layers, most of which are consistent with atmospherically transported sediments [Anderson & Bell, 2010]. The proposed work is relevant to understanding sand dunes, geomorphology and sedimentology at Gale Crater. Our landscape evolution modeling is also relevant to Mars Sample Return. Wind exhumation determines the depth of burial and pressure-temperature-time history of exposed samples, which is key to diagenesis including thermal alteration of organic matter (Farley et al. 2013)

Scientific priorities. The proposed work addresses two of the key questions defined by a recent review paper by members of the Mars sedimentary geology community [Grotzinger et al., 2011]: “How Did Source-to-Sink Sediment Transport Systems Evolve on Mars?”, and “In What Ways Did Martian Sedimentary Rocks Become Modified after Their Deposition?” For example, the Medusae Fossae Formation shows yardangs and mesoscale undulations which may result from the interaction of slope winds with the synoptic flow. The proposed work on slope-wind erosion is relevant (to be expanded) to the origin of sedrocks/stratigraphy on an early mars where wind erosion important, the origin of sand in dunes, the origin(s) of Valles Marineris [Andrews-Hanna, 2012], the growth and form of the ice mounds, the formation of ferric-oxide lags (e.g., Weitz et al., in press, sequence stratigraphy, and the possible universal length scale of moat width.

the similarly weak polar ice deposits have a stratigraphy that strongly suggests strong slope-wind erosion at both ~10^1 and 10^2 km scale

Main records of long-term climate change on Mars come from sedimentary rocks, but the sedimentary rocks that we can sample are a wind-eroded subset of the original extent. Not knowing the pattern and process of wind erosion that sets extent of the sedimentary rocks and the unconformities within them has major implications: are they coastal deposits, evaporites, or indurated loess? Also implications for geochemical reservoirs (Niles VM 2012), polar sedimentation and polar processes, and even tectonics. This motivates the development of a physical model of long-term wind erosion on Mars. Because the winds are strongly influenced by mesoscale terrain (cite REMS here), this implies mesoscale model is appropriate scale.

Coupling between planet-shaping processes. Large-scale exhumation can trigger tectonic uplift, and this has been proposed for the Qaidam Basin on Earth [Kapp et al., 2011] and for Valles Marineris formation [Andrews-Hanna, 2012]. In addition to the equatorial layered sediments that are the focus of this proposal, slope-enhanced winds define both the large-scale and small-scale topography of the north polar layered deposits (Chasma Boreale and spiral troughs) and circum-polar ice mounds, and played an important role in landscape evolution there [Holt et al., 2010; Smith & Holt, 2010; Conway et al., 2012, Brothers et al. 2013, Smith & Holt?].

Layered sediments are the best available archives of long-term environmental change on Mars, but they constitute a wind-eroded subset of the original deposits. Wind erosion is actively abrading the layered sediments today, and Our lack of understanding of the role of wind erosion in shaping the sedimentary rocks has major implications for the interpretation of the sedimentary rocks (are they coastal deposits, evaporites sourced by groundwater upwelling, or

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indurated windblown material?), for geochemical reservoir budgeting and balancing (Niles VM) and even tectonics (Andrews-Hanna).

Possible tentative link to habitability

In theory, one-to-one mapping between a landscape and a pattern of erosion implies that the model can be inverted for past landscapes, as has been demonstrated for channel networks on Earth [Abrams et al., 2009, others?]. In detail, this is not possible for wind erosion on Mars because of umodelled diffusive geologic processes, and especially because the presence of essentially nonerodible material (basalt) leads to degeneracies when the flow of time is reversed. Nevertheless, with care and only for sediment-dominated landscapes such as the MFF, it may be possible to place some constraints on past landscapes.

2.7 Relevance of proposed workOur proposed work will advance knowledge about the effect of the Martian atmosphere on the surface, the effect of terrain on the atmospheric circulation, and links to the growth and form of ancient layered sediments. Therefore, our proposal is within the scope of Solar System Workings call, specifically “Evolution and modification of surfaces: [… D]evelop theoretical […] bases for understanding [physical] features in the context of the varying conditions through time after formation.” Our proposal is highly relevant to Goals III.A.6 and Goal III.A.2 outlined in the Mars Exploration Program Analysis Group (MEPAG) Science Goals Document (and also addresses issues raised in Goals II.A.4 and III.A.3.) Goal III.A.6. is to “Characterize surface-atmosphere interactions on Mars” and Goal IIIA.2. is to “evaluate volcanic, fluvial/laucustrine, hydrothermal, and polar erosion and sedimentation processes that modified the Martian landscape over time.” Our proposal addresses a fundamental atmosphere-surface interaction (wind-induced topographic change, and the feedback on the windfield) that has probably operated throughout Mars history.

2.8 Plan of work, personnel, and responsibilities2.8.1 Work plan

Activities/milestones DeliverablesYear 1 Compile MRAMS on CITerra/Fram. Carry out

idealized-topography runs.• Complete analysis of idealized-topography mesoscale runs.Analyze output to derive parameterization for terrain-induced erosion• Incorporate terrain-induced wind erosion parameterization into landscape evolution model.

✓ LPSC presentation on: Slope winds on idealized topography.✓ Short GRL-length manuscript on: Slope winds on idealized topography and patterns of wind erosion.

Year 2 Carry out realistic-topography runs.•Complete analysis of realistic-terrain mesoscale runs

•Complete parameter sweeps with landscape evolution model.

✓ Detailed manuscript on: Slope enhanced wind erosion on Mars, including realistic terrain.✓ Short GRL-length manuscript on slope-wind erosion/landscape evolution coupling (may be expanded into a detailed manuscript, depending on results).

Year 3

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2.8.2 Planned Calculations and the Parameters ExploredCalculation Mesoscale model runs Landscape evolution model

runsNumber of Calculations ~60 three-dimensional

simulationsTotal: ~500,000 CPU-hours

~ 104 landscape evolution model runsTotal: ≤104 CPU-hours

Parameters Explored (and Sensitivity Tests)

crater/canyon width, pressure, wall slope, mound width, mound height, mound slope exponent, (dust loading, synoptic wind, Coriolis force).

2.7 Personnel and Qualifications (For FTE information, see §6, Budget Justification).PI Edwin Kite is currently a Princeton postdoc and a research associate at the University of Chicago (UChicago); he will be an Assistant Professor at UChicago from 1 Jan 2015. As PI, he will participate to some degree in all aspects of the proposed work and oversee its implementation. Co-I Timothy Michaels will be responsible for implementation and refinement of the MRAMS model of crater-atmosphere interactions; he will contribute to data analysis and paper-writing. Collaborators Scot Rafkin will support Task 2 by (respectively) assisting in the interpretation of the MRAMS model output. A graduate student at UChicago will carry out a substantial portion of the geologic mapping work, and assist in constructing DTMs. Depending on the interests and aptitude of the student, they may also take part in running and analyzing the MRAMS models. All personnel will participate in interpretation of results. A planetary GIS/data specialist at UChicago will support GIS and data integration for all tasks, and will assist in DTM production; no funds are requested for this specialist, who will be supported by UChicago through Kite’s startup funds. The PI, Co-I, and Collaborator Rafkin have worked together to publish two papers relevant to this proposal and using the same model (Kite, Michaels, Rafkin et al. 2011a; Kite, Rafkin, Michaels et al. 2011b). That work was carried out and published while Kite was a graduate student at UC Berkeley, and was funded by NASA grants NNX08AN13G and NNX09AN18G.

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4. Biographical Sketches

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Michaels (1 page limit)

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Rafkin (1 page limit)

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5. Current and pending support

Kite Current and Pending SupportTitle: Harry Hess Fellowship Sponsoring: Princeton prize fellowship. Contact Nora Zelizer, 609-258-5809, nelizer@princeton.eduPeriod: January 1, 2014 – December 31, 2014Annual effort: Full-time fellowship (12.0 months)

Michaels Current and Pending Support (required)

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6. Statements of commitmentRequired from all parties: Kite, Michaels, Rafkin

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6. Budget Justification.

6.1. Budget narrativeThis proposal requests funds for direct labor, travel, and publication expenses for a three year study of wind erosion and landscape evolution on Mars. The Principal Investigator (Edwin Kite) will be a full-time employee of the University of Chicago throughout the performance period, with salary for 9 months per year paid by the University. Kite is budgeted 0.5 months of summer salary per year for this project. Kite is contractually limited to 2 months of summer salary (integrated across all externally-funded projects). The Co-Investigator (Tim Michaels) is budgeted for 2 months per year in order to support the refinement and execution of the numerical model. A full time Graduate Student at UChicago is budgeted for 4 months of support in year 1 while they are trained on the data analysis workflow, and then for 9 months of support each remaining year. (The recruitment of the grad student is contingent on the successful selection of the proposal.) These budgeted amounts are commensurate with the level of effort to be put into the proposed work; for further details, please see the table below. Funds are not requested for the Collaborator (Nathan Bridges). While the team consists of several members, each brings an area of (complementary) expertise necessary for achieving the goals of this proposal (§2.7 and §6.1.1). Funds are requested to cover the publication charges for one publication per year (the Plan of Work, §2.8 in this proposal, explains the intended subject matter of publications and their allocation between Tasks). This type of publication is the most direct way for the knowledge gained from this work to be disseminated to and shared with the scientific community. We anticipate our publication costs will exceed the budgeted amount, and extra publication costs will be covered by PI Kite’s startup funds.

Funds are requested for the graduate student (in Years 2 and 3) to attend the annual LPSC meeting and present the research findings. The PI, Co-I and Collaborator Rafkin have successfully collaborated on past projects with minimal face-to-face meetings and therefore no funds are requested to finance research visits between institutions.

7.1.1. Personnel and work efforts.Proposal role Year 1 Year 2 Year 3

Edwin Kite Principal Investigator

1.0 mo 1.0 mo 1.0 mo

Timothy Michaels

Co-Investigator 2.0 mo 2.0 mo 2.0 mo

Nathan Bridges CollaboratorGraduate student 4 mo 8 mo 8 mo

David Mayer GIS/data specialist 1 mo 1 mo 1 mo

7.1.2. Facilities and equipment.No funds are requested for the full time GIS/Planetary data specialist at UChicago. The expected work effort for this individual is 1 months per year as they build DTMs and support the GIS analysis. UChicago, through Kite’s startup account, will guarantee that the GIS specialist will be available for the work specified.

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The proposed work entails extensive model development and will require significant CPU-time. The more computer-intensive (mesoscale) models will be carried out on the Midway cluster at U. Chicago. From our earlier collaboration [Kite et al. 2011a, 2011b], we expect ≤1 CPU month per idealized-terrain simulation and ~2 CPU months per Valles Marineris simulations. The PI owns a dedicated partition on Midway that is sufficient, and in addition the Research Allocation Request can provide more CPUs.

In the past the proposal team has successfully published papers based on runs using MRAMS in serial mode on multicore desktop Linux boxes. For this proposal, we will use a portion of the 72 cores on the UChicago ‘Midway’ HPC cluster that Kite has designated for purchase using his startup funds; this provides ample headroom for calculations in addition to the proposed 71-run parameter sweep if this is suggested by the data analysis. Co-I Michaels also owns a modest cluster that will be used for testing and development work in support of the proposed study. We have confirmed that Co-I Michaels can be provided with an account on the UChicago cluster that will allow seamless collaboration on Task 2.

RAM limitations preclude running more than 2 MRAMS instances simultaneously on any given 16-core node. (~60 model runs are required, ~1 core-month per model run). We also have access to a ~3 desktop workstations at U. Chicago, which is sufficient for the less computer-intensive landscape evolution models and which we can use without charge.

Computer requirements for model calculations/data processing: We will examine 4 water vapor fluxes, 3 atmospheric pressures, 2 orbital/seasonal forcings, 3 dust loading conditions, for a total of 48 sets of 3D mesoscale conditions. We will carry out 1 high-resolution test and 22 other check runs. We will run ~7 simulated sols for each set of simulated conditions, at ~500 processor-hours per sol, for a total of ~210,000 processor hours, to be run in parallel on some fraction of our 72-processor cluster. CPU-time savings from parallelization of MRAMS are approximately linear in the number of cores.

6.2. Budget Details

A. Senior/Key PersonnelWe request support for 1 summer month for PI Edwin Kite in each year of the budget. Dr.

Kite will be a full-time Assistant Professor at the University of Chicago during the performance period, with salary for 9 months per year paid by the University.

B. Other PersonnelWe request support for a graduate student research assistant, 4 months in year 1, 8 months

in years 2 and 3. Graduate student research assistant salaries are set each year by the Division of the Physical Sciences at the University of Chicago.

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Fringe Benefits. Fringe benefits are 26.6% of the salaries of the PI and the GIS specialist. No fringe benefits are assessed on the salaries of graduate student research assistants.

Inflation Adjustment. Salaries have been adjusted by 3% per year to allow for inflation. D. Travel

The Lunar and Planetary Science Conference is a cornerstone meeting in planetary sciences. We request support for the following trips to the LPSC. Year 1, PI; Years 2 and 3, Graduate student.

The estimated cost of this annual travel is $1078 in Year 1 and $973 in each of Years 2 and 3. Estimated amounts are based on costs of past conferences and airfare costs for the relevant destinations from Kayak.com. The basis for this estimate is as follows:

1 person, 4 days (PI in Year 1. Graduate student in Years 2 and 3). Departure city Chicago, arrival city HoustonAirfare $287 (based on Kayak search for mid-April 2014; Spirit Airlines.)Per diem $125 (including lodging)Shuttle to Woodlands, TX from airport and return trip $66 (SuperShuttle website)Conference registration fee $225 (professional) in Year 1, $120 (student discount) in Years 2 & 3 (from LPSC website)

F. Other Direct Costs

Publication Costs. $1000 in each year; we anticipate publishing 2 short (GRL-length) and 2 longer (JGR-length) papers in AGU journals (see Section 2.7, Work Plan). The requested costs are in line with the publication charges for these journals.

Subwards. We request a total of $XX,XXX for the subaward to the SETI Institute to perform the work described in the proposal.

Tuition Remission. Graduate student tuition support is requested in accordance with the University of Chicago Physical Sciences Division's established policy of requesting tuition support at the rate of 48% of graduate student salaries. The amount partially covers the graduate student's actual tuition cost.

H. Indirect CostsPer our rate agreement dated 18 January 2013 with our cognizant federal agency, the

Department of Health and Human Services, a rate of 58% is applied to Modified Total Direct Costs for on-campus research activities. MTDC in this budget excludes items F8 (tuition remission) and the amount of F5 (subward) over $25,000. All other items are subject to indirect cost.

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7. Subcontract to the SETI Institute

Statement of Work

Timothy Michaels is a Research Scientist at the SETI Institute. He has extensive experience of Mars mesoscale modeling including the development of microphysical schemes for tracking dust and water ice aerosol. The primary responsibility of Michaels will be to provide needed modifications to the existing Mars Regional Atmospheric Modeling System (MRAMS) model and support the PI in maintaining the code and executing the model.

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SUBCONTRACT BUDGET DETAILS

Department of Earth and Space SciencesUniversity of California, Los Angeles 595 Charles Young Drive East, Box 951567 Los Angeles, CA 90095-1567

Geologic Proxies for Early Mars Atmospheric Pressure and Greenhouse Forcing

Co-Investigator: Jean-Pierre WilliamsRequested Period of Performance: 01/01/2015-12/31/2016Submitted to: University of ChicagoPrinciple Investigator: Dr. Edwin KiteNASA Program: Mars Data Analysis Program

Subcontract Budget Details

01/01/15- 01/01/16-Salaries 12/31/15 12/31/16 Total J.-P. Williams, PI - 1 mos., @100% $6,717 $7,053 $13,770 (Current Salary $6,716.67/mo)Total Salaries $6,717 $7,053 $13,770(Based on current rates with a 5% increase for PI in Years 2 & 3.)Employee Benefits J.-P. Williams 51.59% of salary $3,465 $3,639 $7,104Total Employee Benefits $3,465 $3,639 $7,104(Based on current rates)Total Salaries & Employee Benefits $10,182 $10,692 $20,874

Other Direct Costs Project Supplies & Expenses $0 $0 $0 Technology Infrastructure Fee @$35.42/mo/FTE $35 $35 $70 Travel $0 $0 $0 Publication $0 $0 $0 Computer software $0 $0 $0Total Other Direct Costs $35 $35 $70Total Direct Costs (TDC) $10,217 $10,727 $20,944Indirect Costs: 54% of TDC $5,517 $5,793 $11,310Total UCLA Costs (Direct & Indirect) $15,734 $16,520 $32,254(Based on the agreement between UC and US DHHS Dated 04/27/11. The agreement establishesfacilities and administrative cost of 54% for on-campus research from 07/01/10 to 06/30/16.)

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Budget JustificationDr. Williams is requesting 1 month of salary per year for the first two years, which will be devoted to modifying the Monte Carlo simulation, maintaining the code, and assisting the PI in executing simulations as detailed in the Plan of Work. Dr. Williams has successfully collaborated with Dr. Kite on past projects with minimal face-to-face meetings and therefore no funds are requested to finance research visits between institutions.

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