Active Main-Belt Asteroid (6478) Gault -- Constraint on Its Cohesive Strength and the Fate of Ejected Particles in the Solar System

TL;DR

This study constrains the cohesive strength of asteroid Gault and models the long-term trajectories of ejected particles, suggesting ongoing surface shedding due to rotational instability and potential future impacts.

Contribution

It provides the first detailed constraints on Gault's bulk cohesive strength and models particle trajectories over thousands of years.

Findings

Gault may be close to structural failure at its current spin rate.

Particles of about 100 micrometers can re-impact Gault after several thousand years.

Gault's surface likely has a weak layer over a stronger core.

Abstract

Active asteroid (6478) Gault sheds mass independent of location along its orbit. Rotational instability is considered to induce the observed activities. If this is the case, because Gaults breakup event has not been detected, surface failure is likely, implying its surface materials are constantly ejected while its major body remains intact. Given this scenario, we first constrain Gaults bulk cohesive strength. We then characterize heliocentric trajectories of ejected particles over thousands of years. The results show that Gault may be sensitive to structural failure at the current spin period (~ 2.5 hr). Gaults bulk density needs to be below 1.75 g/cm^3 in order for particles on the equatorial surface to be shed due to centrifugal forces. In this case, Gault requires cohesive strength of at least ~ 200 Pa to maintain the structure at the center, whereas the surface strength needs to be less than ~ 100 Pa to induce mass shedding. This suggests that Gaults structure may consist of a weak surface layer atop a strong core. The trajectories of dust ejected from Gault depend on how efficiently they are accelerated by solar radiation pressure. Escaped particle clouds with sizes on the order of 100 micrometers could collide with Gault after about 700 to 5300 years with speeds of ~ 0.2 km/sec. This implies a temporal increase in the impact flux and complex interactions between the ejected particles and their host body.