The aeolian-erosion barrier for the growth of metre-size objects in protoplanetary discs

Abstract

Aeolian erosion is a destructive process that can erode small-size planetary objects through their interaction with a gaseous environment. Aeolian erosion operates in a wide range of environments and under various conditions. Aeolian erosion has been extensively explored in the context of geophysics in terrestrial planets. Here we show that aeolian erosion of cobbles, boulders, and small planetesimals in protoplanetary discs can constitute a significant barrier for the early stages of planet formation. We use analytic calculations to show that under the conditions prevailing in protoplanetary discs small bodies ($10\!-\!10^4 \, \rm {m}$) are highly susceptible to gas-drag aeolian erosion. At this size-range aeolian erosion can efficiently erode the planetesimals down to tens-cm size and quench any further growth of such small bodies. It thereby raises potential difficulties for channels suggested to alleviate the metre-size barrier. Nevertheless, the population of ∼decimetre-size cobbles resulting from aeolian erosion might boost the growth of larger (>km size) planetesimals and planetary embryos through increasing the efficiency of pebble-accretion, once/if such large planetesimals and planetary embryos exist in the disc.

Rapid destruction of planetary debris around white dwarfs through aeolian erosion

“…Aeolian erosion is a purely mechanical destructive process, which is very common in many occasions in nature, mainly discussed in the context of sand dunes (Bagnold 1941) . Recently, we showed that aeolian erosion can play an important role in planet formation by setting a new growth-barrier for pebbles/boulders in protoplanetary disks, and affecting pebble accretion and streaming instability (Grishin et al 2020;Rozner et al 2020). Aeolian erosion in protoplanetary disks is rapid and efficient, as also verified in lab experiments and numerical simulations of the conditions of protoplanetary disks (Paraskov et al 2006;Demirci et al 2020b;Demirci & Wurm 2020;Demirci et al 2020a;Schaffer et al 2020).…”

“…In this paper we focused on the processes of aeolian erosion, which, to date, were not considered in the context of WD disks. We made use of an analytical model for aeolian erosion in WD disks, based on our studies of such processes in protoplanetary disks as presented in Rozner et al (2020). We find that the typical timescales of aeolian erosion in WD disks are extremely short, with aeolian erosion grinding down even km-size objects within the disk lifetime.…”

“…Above the threshold velocity, i.e. rel > ★ , the aeolian erosion rate is given by (Rozner et al 2020)…”

“…where coh is the cohesion acceleration. The derivation rises from the work done on the eroded object by the shear pressure; see a detailed derivation from equations 8 and 9 of Rozner et al (2020). The derivation is based on estimation of the typical sweeping rate of grains from the outer layer and calculating the work done by them.…”

“…Aeolian erosion leaves signatures on the dynamics of objects in the disk, e.g. it fuels pebble-accretion and induces a redistribution of sizes in the disk, and might potentially lead to reshaping or complete destruction of objects (Grishin et al 2020;Rozner et al 2020). In contrast with protoplanetary disks, the temperatures in WD disks are high enough to maintain thermal ablation (Podolak et al 1988;Pollack et al 1996;D'Angelo & Podolak 2015) along with aeolian erosion, and accelerate the destruction of small objects.…”