An insolation activated dust layer on Mars

Beule, Caroline de; Wurm, Gerhard; Kelling, T.; Koester, Marc; Kocifaj, Miroslav

doi:10.1016/j.icarus.2015.06.002

Cited by 20 publications

(15 citation statements)

References 20 publications

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“…In the following, we assume that an overpressure within the aggregate is responsible for the disintegra- tion. It is worth to mention that this occurs on very small spatial scales but 100 µm scales for pressure induced tension were also seen in recent work by de Beule et al (2015). As a model, we approximate an aggregate as a coremantle structure.…”

Section: Disintegration Modelmentioning

confidence: 60%

Analog Experiments on Tensile Strength of Dusty and Cometary Matter

Musiolik

Beule

Wurm

2017

Icarus

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The tensile strength of small dusty bodies in the solar system is determined by the interaction between the composing grains. In the transition regime between small and sticky dust (µm) and non cohesive large grains (mm), particles still stick to each other but are easily separated. In laboratory experiments we find that thermal creep gas flow at low ambient pressure generates an overpressure sufficient to overcome the tensile strength. For the first time it allows a direct measurement of the tensile strength of individual, very small (sub)-mm aggregates which consist of only tens of grains in the (sub)-mm size range. We traced the disintegration of aggregates by optical imaging in ground based as well as microgravity experiments and present first results for basalt, palagonite and vitreous carbon samples with up to a few hundred Pa. These measurements show that low tensile strength can be the result of building loose aggregates with compact (sub)-mm units. This is in favour of a combined cometary formation scenario by aggregation to compact aggreates and gravitational instability of these units.

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Section: Disintegration Modelmentioning

confidence: 60%

Analog Experiments on Tensile Strength of Dusty and Cometary Matter

Musiolik

Beule

Wurm

2017

Icarus

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“…From thermal calculation, the temperature gradient of a granular medium when the surface is irradiated can be considered as constant at the near surface for a length L x2 (upper domain 2) and then decreases at depth for a length L x1 (lower domain 1) [26]. We can thus estimate the pressure increase at the limit between domain 1 and 2 [26]:…”

Section: Knudsen Pump Modelmentioning

confidence: 99%

“…The precise near-surface temperature field in granular medium has been estimated numerically [24,25], taking into account the penetration depth of incoming light. On Mars, rough estimates of the thermal balance demonstrate that the thermal creep creates an active layer 100-200 microns thick for a particle size of 67 microns [26,27,28]. This effect decreases by 10% the wind speed threshold for saltation.…”

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confidence: 99%

Formation of recurring slope lineae on Mars by rarefied gas-triggered granular flows

et al. 2017

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Active dark flows known as recurring slope lineae have been observed on the warmest slopes of equatorial Mars. The morphology, composition and seasonality of the lineae suggest a role of liquid water in their formation. However, internal and atmospheric sources of water appear to be insufficient to sustain the observed slope activity. Experimental evidence suggests that under the low atmospheric pressure at the surface of Mars, gas can flow upwards through porous Martian soil due to thermal creep under surface regions heated by the sun and disturb small particles. Here we present numerical simulations to demonstrate that such a dry process involving the pumping of rarefied gas in the Martian soil due to temperature contrasts can explain the formation of the recurring slope lineae. In our simulations, solar irradiation followed by shadow significantly reduces the angle of repose due to the resulting temporary temperature gradients over shaded terrain and leads to flow at intermediate slope angles. The simulated flow locations are consistent with observed recurring slope lineae that initiate in rough and bouldered terrain with local shadows over the soil. We suggest that this dry avalanche process can explain the formation of the recurring slope lineae on Mars without requiring liquid water or CO2 frost activity.Dark flow type RSL occurs in the warmest areas of Mars, during the warm season [1,2]. The activity of RSL seems to be linked with solar irradiance. In the ∼11°S latitude of Melas Chasma, the activity is observed mainly around Ls = 90°(Southern hemisphere Winter solstice) at a slope oriented toward North and around Ls = 270°(Southern hemisphere Summer solstice) at a slope oriented toward South [2]. This slope dependent seasonal activity is also confirmed 1

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“…In a low-pressure environment (here, p ≈ 500 Pa) capillaries on the order of the mean free path of the gas molecules and heated on one end efficiently pump gas from the cold to the warm side (Knudsen 1909;Muntz et al 2002, thermal creep). A porous dust aggregate acts like a collection of capillaries (de Beule et al 2015;Koester et al 2017;Steinpilz et al 2017). Therefore, if dust aggregates are placed on a hot surface at low ambient pressure, gas flows from the cold top through the aggregate toward its bottom.…”

Section: Growth Experimentsmentioning

confidence: 99%

Is There a Temperature Limit in Planet Formation at 1000 K?

Demirci¹,

Teiser²,

Steinpilz³

et al. 2017

ApJ

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Dust drifting inward in protoplanetary disks is subject to increasing temperatures. In laboratory experiments, we tempered basaltic dust between 873 K and 1273 K and find that the dust grains change in size and composition. These modifications influence the outcome of self-consistent low speed aggregation experiments showing a transition temperature of 1000 K. Dust tempered at lower temperatures grows to a maximum aggregate size of 2.02 ± 0.06 mm, which is 1.49 ± 0.08 times the value for dust tempered at higher temperatures. A similar size ratio of 1.75 ± 0.16 results for a different set of collision velocities. This transition temperature is in agreement with orbit temperatures deduced for observed extrasolar planets. Most terrestrial planets are observed at positions equivalent to less than 1000 K. Dust aggregation on the millimeter-scale at elevated temperatures might therefore be a key factor for terrestrial planet formation.

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An insolation activated dust layer on Mars

Cited by 20 publications

References 20 publications

Analog Experiments on Tensile Strength of Dusty and Cometary Matter

Analog Experiments on Tensile Strength of Dusty and Cometary Matter

Formation of recurring slope lineae on Mars by rarefied gas-triggered granular flows

Is There a Temperature Limit in Planet Formation at 1000 K?

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