Three fast-spinning medium-sized Hilda asteroids uncovered by TESS

TL;DR

This study identifies three fast-spinning Hilda asteroids using TESS data, revealing their rapid rotation rates challenge previous assumptions and suggest they may have higher densities or cohesion, providing insights into their composition and early solar system dynamics.

Contribution

The paper reports the discovery of three fast-rotating Hilda asteroids with unprecedented short spin periods using TESS data, expanding understanding of their physical properties.

Findings

Three Hilda asteroids with 3.2--3.7 h rotation periods identified.

Fast rotators imply higher densities or cohesion than previously assumed.

Occurrence rate linked to C-type asteroid fraction in Hildas.

Abstract

Hilda asteroids, which orbit in a 3:2 resonance with Jupiter, serve as key indicators of dynamical processes in the early solar system. Their spin rates, an important probe of these mechanisms, can constrain their density and collisional evolution, offering valuable insights into their origin. In this paper, we report on the identification of three fast-rotating Hilda asteroids with spin periods in the 3.2--3.7 h range using data from the Transiting Exoplanet Survey Satellite. These rotation periods are significantly shorter than the previous $\sim$5.0 h shortest rotation periods obtained from ground-based observations in the $\sim$10 km size range, and are comparable with the $\sim$3.0 h breakup limit of Hildas a few km in size, derived from the FOSSIL survey. These fast-rotating asteroids require either considerable cohesion (in the order of a few kPa), or densities $\rho$ $\gtrsim$1.5 $gm^{-3}$, in contrast to the typically assumed $\rho$ $\lesssim$1 $gm^{-3}$, to prevent rotational break-up. C-type asteroids, which are common in the outer main belt, have densities of $\rho$ $\approx$1.5 $gm^{-3}$ and are known to comprise a small but notable fraction of Hildas. The observed occurrence rate of the $\leq$4 h rotation periods may be explained by the 10-15% fraction of C-type asteroids, likely mixed into these populations from the outer main belt during giant planet dynamical interactions in the early solar system.