The vector alignments of asteroid spins by thermal torques

Area of Science:

• Asteroid dynamics
• Solar system science
• Planetary geology

Background:

• Collisions were traditionally considered the primary factor in altering asteroid rotation.
• The Koronis asteroid family, formed by a major collision, was expected to exhibit random rotational axes due to subsequent impacts.

Purpose of the Study:

• To investigate the observed non-random spin states and rotation periods within the Koronis asteroid family.
• To determine the dominant mechanism responsible for modifying asteroid spin states.

Main Methods:

• Analysis of observational data for the Koronis asteroid family.
• Modeling the effects of thermal torques on asteroid spin states and orientations.
• Investigating potential spin-orbit resonances.

Main Results:

• Observed Koronis family members with prograde spins show similar periods (7.5-9.5 h) and obliquities (42-50 degrees).
• Retrograde spinners exhibit distinct obliquities (154-169 degrees) and broader period distributions (<5 h or >13 h).
• Thermal torques successfully explain these non-random orientations and spin rates, including trapping in spin-orbit resonances.

Conclusions:

• Thermal torques are a significant, potentially dominant, factor in modifying the spin states of asteroids smaller than 40 km.
• Collisions may play a lesser role than previously assumed for smaller asteroid spin evolution.
• Thermal torques can influence asteroid shapes over time.