Gas Pressure Driven Screening Forces and Pebble Aggregation: A Pathway for Growth in Planet Formation

TL;DR

This paper introduces a novel gas pressure-driven screening force that enhances pebble aggregation in protoplanetary disks, potentially accelerating planetesimal formation and overcoming key growth barriers.

Contribution

It identifies a previously unrecognized screening force from thermal gas particle shielding that promotes pebble binding independently of surface adhesion, aiding planet formation.

Findings

Screening forces are most effective in the middle disk regions (~0.3 to few AU).

Pebble growth from centimeter to kilometer scales can occur within ~10^5 years.

Growth naturally terminates when smaller particles are depleted, preventing runaway accretion.

Abstract

The formation of planetesimals from cm-sized pebbles in protoplanetary disks faces significant barriers, including fragmentation and radial drift. We identify a previously unaccounted screening force, arising from mutual shielding of thermal gas particles between pebbles when their separation falls below the gas mean free path. This force facilitates pebble binding, overcoming key growth barriers under turbulent disk conditions. Unlike conventional mechanisms, screening forces operate independently of surface adhesion and complement streaming instability and pressure traps by enhancing aggregation in high-density regions. Our analysis predicts that screening interactions are most effective in the {middle disk regions ($ \sim 0.3$ to few AU),} consistent with ALMA observations (e.g., TW Hya) of enhanced dust concentrations. {Furthermore, we find that screening-induced pebble growth from centimeter to kilometer scales can occur on timescales significantly shorter than the disk lifetime ($\sim 10^5$ years). Importantly, this growth naturally terminates when particles smaller than the local gas mean free path are depleted, thereby avoiding runaway accretion.} Beyond planetary science, the screening forces have {potential} implications for high-energy astrophysics, dusty plasmas, confined particle suspensions and other relevant areas, suggesting a broader fundamental significance.