Martian Mantle Heat Flow Estimate From the Lack of Lithospheric Flexure in the South Pole of Mars: Implications for Planetary Evolution and Basal Melting

Ojha, L.; Karimi, Saman; Buffo, Jacob; Nerozzi, S.; Holt, J. W.; Smrekar, S. E.; Chevrier, V. F.

doi:10.1029/2020gl091409

Cited by 27 publications

(40 citation statements)

References 70 publications

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“…In this study, we predict a maximum flexure beneath the south polar cap of 770 m that is smaller than, though still consistent with, that used in Ojha et al. (2021). Although both studies use somewhat similar constraints, Ojha et al.…”

Section: Surface Heat Flow In the South Polar Regionsupporting

confidence: 91%

“…Although both studies use somewhat similar constraints, Ojha et al. (2021) made use of a more detailed elasto‐viscoplastic deformation model, and determined that the mantle heat flow at the base of the lithosphere should be less than 10 mW

m^{- 2}

. Their upper limit lies in the range of possible solutions we find in this study, which is a mantle heat flow of less than 15 mW

m^{- 2}

.…”

Section: Surface Heat Flow In the South Polar Regionmentioning

confidence: 52%

“…(2020) have a dielectric constant of about 3 and higher and would not generate basal relief anti‐correlated with the surface topography, in contrast to what was suggested by Ojha et al. (2021). If such a larger quantity of

{CO}_{2}

ice in fact exists, in order not to be detectable as radar reflections, it would be required to be in the form of thin layers, with a thickness less than several times the SHARAD and MARSIS resolutions (a few meters, see Lalich & Holt, 2017).…”

Section: Discussionmentioning

confidence: 65%

“…Another possibility is that Ojha et al. (2021) overestimated the total stress of the polar cap acting on the lithosphere, as a result of their using a simple one‐dimensional axisymmetric stress profile for the load, when the polar cap is in fact highly non‐axisymmetric. As an example, if the stress were 25% lower, a mantle heat flow of about 13 mW

m^{- 2}

would be accepted, which would be closer to our estimate.…”

Section: Surface Heat Flow In the South Polar Regionmentioning

confidence: 99%

“…The two polar caps further act as large‐scale loads that can bend the crust and lithosphere (Broquet et al., 2020), and are likely the only million years old surface features on Mars that could generate a measurable deflection. Lacking in situ heat flow estimates, analysis of the lithospheric flexure beneath these two polar caps is one of the only methods that give access to the present‐day strength of the lithosphere, which is related to the thermal state of the planet (Ojha et al., 2021; Phillips et al., 2008) and the thickness of the crust and its heat production (Plesa et al., 2018; Thiriet et al., 2018).…”

Section: Introductionmentioning

confidence: 99%

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

Broquet

Wieczorek

2021

JGR Planets

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The flexure of the lithosphere under stresses imposed by the geologically young south polar cap is one of the few clues we have regarding the south polar cap composition and the present‐day thermal state of Mars. Here, we combine radar, gravity, and topography data with a flexural loading model to estimate the bulk density (ρ) and average real dielectric constant (ε′) of the south polar cap, and the elastic thickness of the lithosphere (Te). Given the uncertainties of the data, our results constrain ρ to be 1,100–1,300 kg m−3 (best fit of 1,220 kg m−3), ε′ to be 2.5–3.4 (best fit of 3.3), and Te to be greater than 150 km (best fit of 360 km). Based on these results, the maximum lithospheric flexure is 770 m, and the polar cap volume could be up to 26% larger than previous estimates that did not account for lithospheric flexure. Our inferred compositions imply that the dust concentration would be at least 9 vol% if the CO2 ice content were negligible, and that the CO2 ice concentration would be more than the known 1 vol% CO2 if the dust concentration were less than 9 vol%. The 1‐σ lower limit on Te implies a surface heat flow that is less than 23.5 mW m−2. This lower limit is significantly less than the range of acceptable values at the north pole (330–450 km, heat flow of 11–16 mW m−2), and helps satisfy global thermal evolution simulations that predict hemispheric differences in surface heat flow.

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Section: Surface Heat Flow In the South Polar Regionsupporting

confidence: 91%

m^{- 2}

. Their upper limit lies in the range of possible solutions we find in this study, which is a mantle heat flow of less than 15 mW

m^{- 2}

.…”

Section: Surface Heat Flow In the South Polar Regionmentioning

confidence: 52%

{CO}_{2}

Section: Discussionmentioning

confidence: 65%

m^{- 2}

would be accepted, which would be closer to our estimate.…”

Section: Surface Heat Flow In the South Polar Regionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Broquet

Wieczorek

2021

JGR Planets

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Partially-Saturated Brines Within Basal Ice or Sediments can Explain the Bright Basal Reflections in the South Polar Layered Deposits

Pettinelli

Lauro

et al. 2022

Preprint

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The Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument on Mars Express has detected strong subsurface radar reflections in the region of Ultimi Scopuli (81°S, 193°E), within the South Polar Layered Deposits (SPLD) (Lauro et al., 2021;Orosei et al., 2018). These subsurface reflections are ∼10 dB greater in power than the surrounding reflections and ∼3 dB greater than the reflections from the surface (Orosei et al., 2018). The reflectors are located at the base of the SPLD, approximately 1.5 km below the topographic surface. Because data acquired by MARSIS do not separate the real (ε′) and imaginary (ε″) parts of the complex permittivity of reflectors, the apparent permittivity (ε a ), a single parameter accounting for both ε′ and ε″ (Mattei Abstract Strong radar reflections have been previously mapped at the base of the Martian South Polar Layered Deposits. Here, we analyze laboratory measurements of dry and briny samples to determine the cause of this radar return. We find that liquid vein networks consisting of brines at the grain boundaries of ice crystals can greatly enhance the electrical conductivity, thereby causing strong radar reflections. A brine concentration of 2.7-6.0 vol% in ice is sufficient to match the electrical properties of the basal reflection as observed by Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS). When brine is mixed with sediments, the brine-ice mixture in the pores must be 2-5 times more concentrated in salt, increasing the brine concentration to 6.3-29 vol%. Our best fit of the median observed MARSIS value suggests a salt-bulk sample concentration of ∼6 wt%. Thus, salt enhancement mechanisms on the order of a magnitude greater than the Phoenix landing site are needed. To form brine, the basal reflector must reach a temperature greater than the eutectic temperature of calcium perchlorate of 197.3 ± 0.2 K, which may be possible if more complex thermal modeling is assumed. Colder metastable brines are possible, but stability over millions of years remains unclear. Conversely, gray hematite with a concentration of 33.2-59.0 vol% possess electrical properties that could cause the observed radar returns, but require concentrations 2-3 times larger than anywhere currently detected. We also argue that brines mixed with high-surface-area sediments, or dry red hematite, jarosite, and ilmenite cannot create the observed radar returns at low temperatures.Plain Language Summary Previous research has detected strong radar reflections from the interface between Mars' southern ice cap and their underlying sediments over a region with an area of 20 × 30 km and 1.5 kms beneath the surface. Radar reflections are caused by changes in electrical properties. Here, we analyze electrical property laboratory measurements of materials under Mars-like conditions. We find that a small amount of brine in ice samples could create strong radar reflections similar to those that are observed. A greater concentration of salt is needed in sediment-ice mixtures. We su...

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