The Composition of the South Polar Cap of Mars Derived From Orbital Data

Broquet, A.; Wieczorek, M. A.; Fa, Wenzhe

doi:10.1029/2020je006730

Cited by 22 publications

(28 citation statements)

References 64 publications

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“…The first step is to compute the gravitational attraction that arises from density interfaces beneath the rigid lithosphere of the planet. These interfaces are assumed to be in hydrostatic equilibrium beneath a depth of 150 km, which corresponds to the minimum present‐day thickness of the elastic lithosphere beneath the south polar cap (Broquet et al., 2021). Unless otherwise specified, the lithosphere in this study will refer to that portion of the planet that can support deviatoric stresses over geologic time.…”

Section: Global Crustal Thickness Modelingmentioning

confidence: 99%

InSight Constraints on the Global Character of the Martian Crust

et al. 2022

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Analyses of seismic data from the InSight mission have provided the first in situ constraints on the thickness of the crust of Mars. These crustal thickness constraints are currently limited to beneath the lander that is located in the northern lowlands, and we use gravity and topography data to construct global crustal thickness models that satisfy the seismic data. These models consider a range of possible mantle and core density profiles, a range of crustal densities, a low-density surface layer, and the possibility that the crustal density of the northern lowlands is greater than that of the southern highlands. Using the preferred InSight three-layer seismic model of the crust, the average crustal thickness of the planet is found to lie between 30 and 72 km. Depending on the choice of the upper mantle density, the maximum permissible density of the northern lowlands and southern highlands crust is constrained to be between 2,850 and 3,100 kg m −3 . These crustal densities are lower than typical Martian basaltic materials and are consistent with a crust that is on average more felsic than the materials found at the surface. We argue that a substantial portion of the crust of Mars is a primary crust that formed during the initial differentiation of the planet. Various hypotheses for the origin of the observed intracrustal seisimic layers are assessed, with our preferred interpretation including thick volcanic deposits, ejecta from the Utopia basin, porosity closure, and differentiation products of a Borealis impact melt sheet. Plain Language SummaryThe crust, mantle and core are the three major geochemical layers that make up a planet. Before NASA's InSight mission, the thickness of the crust of Mars was inferred using indirect techniques, including analyses of gravity data collected from orbit and the composition of surface rocks. Estimates for the average thickness using these techniques spanned the range from 27 to 118 km. Analyses of data collected by the InSight seismometer have provided us with the first direct seismic measurement of the thickness of the crust, but this measurement is only for beneath the lander that is located in the northern lowlands where the crust is expected to be thinner than average. In this work, gravity and topography data are used to construct global crustal thickness models that satisfy the new seismic constraints. The average crustal thickness is found to be somewhere between 32 and 70 km, and the average density of the crust can be no larger than 3,100 kg m −3 . This bulk crustal density is lower than most typical Martian WIECZOREK ET AL.

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Section: Global Crustal Thickness Modelingmentioning

confidence: 99%

InSight Constraints on the Global Character of the Martian Crust

et al. 2022

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“…This has been concluded based on the lack of downward deflection with uncertainties of 100-200 m, beneath the north polar cap as seen by MARSIS and SHARAD radars Phillips et al (2008), while for the south polar cap a maximum lithospheric flexure of 770 m has been found (Broquet et al, 2021). Previous elastic lithosphere thickness estimates with values larger than 300 km for the north pole (Phillips et al, 2008) and larger than 150 km for the south pole (Wieczorek, 2008) have been reevaluated in two recent studies (Broquet et al, 2020(Broquet et al, , 2021. The latest estimates indicate an elastic thickness between 330 km and 450 km for the north pole of Mars (Broquet et al, 2020) and a value larger than 150 km with a best fit of 360 km for the south pole Broquet et al (2021).…”

Section: Symbolmentioning

confidence: 87%

“…On the other hand, present-day elastic thickness estimates that are available for the north pole and the south poles of Mars indicate a much thicker and colder lithosphere at these two locations. This has been concluded based on the lack of downward deflection with uncertainties of 100-200 m, beneath the north polar cap as seen by MARSIS and SHARAD radars Phillips et al (2008), while for the south polar cap a maximum lithospheric flexure of 770 m has been found (Broquet et al, 2021). Previous elastic lithosphere thickness estimates with values larger than 300 km for the north pole (Phillips et al, 2008) and larger than 150 km for the south pole (Wieczorek, 2008) have been reevaluated in two recent studies (Broquet et al, 2020(Broquet et al, , 2021.…”

Section: Symbolmentioning

confidence: 96%

“…Throughout this study we illustrate how model results can be related to available geological and geophysical observations. For our models we use both global constraints such as the thermal lithosphere thickness (Khan et al, 2021) and estimates of the tidal deformation of Mars (Genova et al, 2016;Konopliv et al, 2016Konopliv et al, , 2020, as well as local data sets, such as the present-day elastic lithosphere thicknesses at the north and south poles (Phillips et al, 2008;Wieczorek, 2008;Broquet et al, 2020Broquet et al, , 2021 and the location of partial melt that could explain recent volcanic activity in Tharsis and Elysium volcanic centers. We highlight how our knowledge of the thermal history and present-day state of the interior has improved with the recent InSight results and discuss what future models need to address in order to further constrain the thermal evolution of Mars.…”

Section: Introductionmentioning

confidence: 99%

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Interior Dynamics and Thermal Evolution of Mars -- a Geodynamic Perspective

Plesa¹,

Wieczorek²,

Knapmeyer³

et al. 2022

Preprint

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Over the past decades, global geodynamical models have been used to investigate the thermal evolution of terrestrial planets. With the increase of computational power and improvement of numerical techniques, these models have become more complex, and simulations are now able to use a high resolution 3D spherical shell geometry and to account for strongly varying viscosity, as appropriate for mantle materials. In this study we review global 3D geodynamic models that have been used to study the thermal evolution and interior dynamics of Mars. We discuss how these models can be combined with local and global observations to constrain the planet's thermal history. In particular, we use the recent InSight estimates of the crustal thickness, upper mantle structure, and core size to show how these constraints can be combined with 3D geodynamic models to improve our understanding of the interior dynamics, present-day thermal state and temperature variations in the interior of Mars. Our results show that the crustal thickness variations control the surface heat flow and the elastic thickness pattern, as well as the location of melting zones in the present-day martian mantle. The lithospheric temperature and the seismic velocities pattern in the shallow mantle reflect the crustal thickness pattern. The large size of the martian core leads to a smaller scale convection pattern in the mantle than previously suggested. Strong mantle plumes that produce melt up to recent times become focused in Tharsis and Elysium, while weaker plumes are distributed throughout the mantle. The thickness of the seismogenic layer, where seismic events can occur, can be used to discriminate between geodynamic models, if the source depth and location of seismic events is known. Furthermore model predictions of present-day martian seismicity can be compared to the values measured by InSight. Future models need to consider recent estimates from the presentday elastic lithosphere thickness at the north pole of Mars, the effects of lateral variations of seismic velocities on waves propagation through the mantle and lithosphere, and to test the spatial distribution of seismicity by comparing model predictions to observations.

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“…The amount of salt required to either suppress the freezing point of water or for deliquescence to play the main role in maintaining this lake are nonphysical (Sori & Bramson, 2019). While localized heating could generate liquid water (Sori & Bramson, 2019), the highlands have inferred low mantle heat flow (Broquet et al., 2021; Ojha et al., 2021). The putative lake locations do not correspond to the minimum hydrological potential expected from basal topography (Arnold et al., 2019), potentially due to the relatively recent formation of the main lake (Orosei et al., 2018).…”

Section: Introductionmentioning

confidence: 99%

Geologic Context of the Bright MARSIS Reflectors in Ultimi Scopuli, South Polar Layered Deposits, Mars

Landis¹,

Whitten²

2022

Geophysical Research Letters

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Radar‐bright basal reflectors have been detected below the South Polar Layered Deposits (SPLD), using Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) data and have an exciting but controversial interpretation: liquid water from subglacial lakes. We mapped the surface of the SPLD immediately above and surrounding the putative lakes (1:2M map scale) in order to provide a geologic context for the interpretation of bright basal reflectors. We use Thermal Emission Imaging System daytime IR (100 m/pixel), Context Camera (6 m/pixel), and High Resolution Imaging Science Experiment (25 cm/pixel) data to characterize geologic units and typical surface roughness. We find evidence for multiple geologic units with features due to CO2 and aeolian‐related processes. We do not find evidence for surface modification linked to postulated lake locations. This is not consistent with the interpretation of the MARSIS basal radar reflector as subglacial lakes.

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The Composition of the South Polar Cap of Mars Derived From Orbital Data

Cited by 22 publications

References 64 publications

InSight Constraints on the Global Character of the Martian Crust

InSight Constraints on the Global Character of the Martian Crust

Interior Dynamics and Thermal Evolution of Mars -- a Geodynamic Perspective

Geologic Context of the Bright MARSIS Reflectors in Ultimi Scopuli, South Polar Layered Deposits, Mars

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