Are Pebble Pile Planetesimals Doomed?

Abstract

In parabolic flight experiments we studied the wind induced erosion of granular beds composed of spherical glass beads at low gravity and low ambient pressure. Varying g-levels were set by centrifugal forces. Expanding existing parameter sets to a pressure range between p = 300 − 1200 Pa and to g-levels of g = 1.1 − 2.2 m s −2 erosion thresholds are still consistent with the existing model for wind erosion on planetary surfaces by Shao & Lu (2000). These parameters were the lowest values that could technically be reached by the experiment. The experiments decrease the necessary range of extrapolation of erosion thresholds from verified to currently still unknown values at the conditions of planetesimals in protoplanetary discs. We apply our results to the stability of planetesimals. In inner regions of protoplanetary discs, pebble pile planetesimals below a certain size are not stable but will be disassembled by a head wind.

Planetesimals in rarefied gas: wind erosion in slip flow

“…The reason for choosing this sample is that they behave like pebbles with low cohesion on pebble pile planetesimals. This sample was also used by Demirci et al (2019), so that the results can be compared with their data.…”

“…This technique is called particle tracking velocimetry and is often used for gas flow characterizations at small ambient pressures (Musiolik et al 2018;Demirci et al 2019;Kruss et al 2019). We use the Fiji plug-in TrackMate as tracking tool (Schindelin et al 2012;Tinevez et al 2017) like Demirci et al (2019) and Schneider et al (2019). Sample spheres, which are lifted by the wind, couple to the gas and are accelerated in flow direction within the coupling time t c .…”

“…We included the low gravity measurements by Demirci et al (2019) which used the same particle sample. The data show that…”

Lifting grains by the transient low pressure in a martian dust devil

“…on the order of γ = 0.01 J/m 2 or even larger for silicates (Kimura et al 2015;Steinpilz et al 2019). On the other side, wind tunnel experiments are often more consistent with a surface energy which is orders of magnitude lower or γ = 10 −4 J/m 2 (Shao & Lu 2000;Kruss et al 2019;Demirci et al 2019). This is not a contradiction though.…”

Wind erosion on Mars and other small terrestrial planets

“…The experimental setup is shown in Fig. 1 and is the same which was used by Musiolik et al (2018) and Demirci et al (2019). For details, the reader is referred to these studies.…”