Venus: Concentrations of radar-reflective minerals by wind

Greeley, R.; Marshall, John R.; Clemens, Drew; Dobrovolskis, Anthony R.; Pollack, James B.

doi:10.1016/0019-1035(91)90074-4

Cited by 11 publications

(4 citation statements)

References 17 publications

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“…For example, the long, radar-bright streaks originating from small bright hills shown in Figures 14a and 14b Because of their relatively high density, they may form "lag" deposits from which lower-density particles have been removed by the wind. Wind tunnel experiments to simulate Venus show that lag deposits could form under Venusian conditions [Greeley et al, 1991]. Such preferential wind winnowing would be expected on Venus in the wake of the hills seen in Figures 14a and 14b, and the hills could also be the source of the radar-reflective material.…”

Section: Wind Streak Distributionmentioning

confidence: 91%

Aeolian features on Venus: Preliminary Magellan results

et al. 1992

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Magellan synthetic aperture radar data reveal numerous surface features that are attributed to aeolian, or wind processes. Wind streaks are the most common aeolian feature. They consist of radar backscatter patterns that are high, low, or mixed in relation to the surface on which they occur. A data base of more than 3400 wind streaks shows that low backscatter linear forms (long, narrow streaks) are the most common and that most streaks occur between 17øS to 30øS and 5øN to 53øN on smooth plains. Moreover, most streaks are associated with deposits from certain impact craters and some tectonically deformed terrains. We infer that both of these geological settings provide fine particulate material that can be entrained by the low-velocity winds on Venus. Turbulence and wind patterns generated by the topographic features with which many streaks are associated can account for differences in particle distributions and in the patterns of the wind streaks. Thus, some high backscatter streaks are considered to be zones that are swept free of sedimentary particles to expose rough bedrock; other high backscatter streaks may be lag deposits of dense materials from which low-density grains have been removed (dense materials such as ilmenite or pyrite have dielectric properties that would produce high backscatter patterns). Wind streaks generally occur on slopes

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Section: Wind Streak Distributionmentioning

confidence: 91%

Aeolian features on Venus: Preliminary Magellan results

et al. 1992

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“…The characteristics of saltation on these planetary bodies differ from those on Earth and depend on factors such as gravity, air density, viscosity, and the properties of the granular material being transported. Whereas terrestrial sand is composed primarily of silicon dioxide quartz with a density of 2650 kg/m 3 , both martian (Yen et al 2005, Golombek et al 2006b) and Venusian (Greeley et al, 1991;Basilevsky and Head, 2003) sand is most likely predominantly basalt, which has a density of approximately 3000 kg/m 3 (Johnson and Olhoeft, 1984). The granular material transported in saltation on Titan is rather different from that on Earth, Mars, and Venus, and likely consists of a mixture of ice and tholins (organic heteropolymers formed by ultraviolet irradiation of organic compounds; Imanaka et al 2004, McCord et al 2006), which has a density substantially lighter than basalt and quartz.…”

Section: Saltation On Mars Venus and Titanmentioning

confidence: 99%

The physics of wind-blown sand and dust

Kok¹,

Parteli²,

Michaels³

et al. 2012

Rep. Prog. Phys.

1,004

1,109

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The transport of sand and dust by wind is a potent erosional force, creates sand dunes and ripples, and loads the atmosphere with suspended dust aerosols. This paper presents an extensive review of the physics of wind-blown sand and dust on Earth and Mars. Specifically, we review the physics of aeolian saltation, the formation and development of sand dunes and ripples, the physics of dust aerosol emission, the weather phenomena that trigger dust storms, and the lifting of dust by dust devils and other small-scale vortices. We also discuss the physics of wind-blown sand and dune formation on Venus and Titan.

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“…Such conductive minerals are rarely as abundant as 9 vol % in primary basalts, but under some circumstances, secondary processes can sort and concentrate them. Greeley et al [1991] have proposed ' that aeolian sorting of disaggregated mineral grains on Venus: could account for the low emissivity observed on mountain tops. They carried out wind tunnel experiments which showed the local abundance of dense minerals can be enhanced by factors up to 8 by this effect.…”

Section: In Section 44 We Argue That Basalt Is the Dominant Primary mentioning

confidence: 99%

Mineral equilibria and the high radar reflectivity of Venus mountaintops

Klose¹,

Wood²,

Hashimoto³

1992

J. Geophys. Res.

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We studied the relationship between altitude and microwave emissivity (the complement of power reflectivity) in 10 highland regions of Venus, using the Magellan data set. Above a critical altitude that ranges from 4.75 km on Maxwell Montes to 2.49 km on Sapas Mons, emissivity undergoes an abrupt decrease to values so low (<0.6) that the surface mineralogy on these mountaintops must differ from that at lower altitudes in such a way as to enhance the bulk dielectric constant of the highland surface material. This emissivity effect probably is produced not by basalt minerals but by a secondary, weathered mineral assemblage. We developed the phase diagrams descriptive of equilibrium secondary mineral assemblages on Venus, as a function of altitude and atmospheric redox state. The mineral responsible for low emissivity on mountaintops appears to be the electrical semiconductor pyrite (FeS2). Variation from one highland area to another in the altitude at which pyrite becomes the stable Fe mineral (as opposed to magnetite at lower altitudes) may be attributable to local modulation by topography of the atmospheric thermal profile. The altitudes at which the magnetite/pyrite phase boundary is encountered vary with the redox slate of the atmosphere, and observed values of this altitude can be used to estimate an oxygen fugacity at plains level of ∼10−21 bars. Maat Mons, a volcanic peak almost as lofty as Maxwell Montes, is the only high mountaintop on Venus that has not weathered to a low‐emissivity mineral assemblage. Presumably, this means flows at the highest altitudes are negligibly weathered and the volcano is relatively young.

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Venus: Concentrations of radar-reflective minerals by wind

Cited by 11 publications

References 17 publications

Aeolian features on Venus: Preliminary Magellan results

Aeolian features on Venus: Preliminary Magellan results

The physics of wind-blown sand and dust

Mineral equilibria and the high radar reflectivity of Venus mountaintops

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