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

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 Gault's breakup event hasn't 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 Gault's 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). Gault's 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 Gault's 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 of <∼ 100µm could collide with Gault after ∼ 700 − 5, 300 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.