A dedicated survey of fast-rotating near-Earth asteroids with the Two-meter Twin Telescope. I. Observational strategy and first results

TL;DR

This study systematically surveyed small near-Earth asteroids using high-cadence photometry, revealing that fast rotation is common among objects smaller than tens of metres and providing insights into their internal strength and structural properties.

Contribution

First systematic survey of small NEA rotation using the Two-meter Twin Telescope, significantly expanding the sample of known fast rotators and their properties.

Findings

Majority of small NEAs are fast rotators, especially below 26th magnitude.

Most objects require cohesive strength exceeding rubble pile limits.

Fast rotation prevalence increases with decreasing asteroid size.

Abstract

The rotational properties of small near-Earth asteroids (NEAs) provide crucial insights into their internal structure and collisional history. However, systematic surveys targeting metre- to decametre-sized bodies are rare, thus leaving their spin distribution poorly constrained. Our aim was to quantify the prevalence of fast rotation and characterise the spin-rate distribution of small NEAs to constrain their internal strength and evolution. We conducted a dedicated high-cadence photometric survey of 249 NEAs using the Two-meter Twin Telescope (TTT). Rotation periods and amplitudes were derived from dense time series to classify objects as fast or non-fast rotators. We determined the rotation period of 156 new fast rotators (P < 2.2 h), including 87 that rotate faster than 10 min. The prevalence of fast rotators increases with absolute magnitude: from 60.6-80.3 % for 22 < H < 24 to 77.3-89.4 % for 24 < H < 26 and 94.1-96.1 % for H > 26, indicating that fast rotation dominates in the small NEA population. Most objects spin faster than the gravity-defined limit; 98 targets require cohesive strengths exceeding that of weak rubble piles, and 22 are compatible only with compact, high-strength interiors. This is the first systematic survey targeting the rotation of such small NEAs, providing the largest homogeneous sample of fast rotators obtained by a single campaign. Our findings demonstrate that fast rotation is the norm for objects smaller than tens of metres, implying that modest cohesive strength is required to prevent their rotational disruption.