Evolution of ejecta in the (65803) Didymos system driven by the fast-spin primary

Stability conditions, mass transfer, and orbiting disk

¹ Instituto de Física Aplicada a las Ciencias y la Tecnología, Universidad de Alicante (UA), Alicante, Spain
² Observatorio Astronómico, Universidad Nacional de Córdoba, Córdoba, Argentina
³ Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina
⁴ Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, Alicante, Spain
⁵ Dipartimento de Fisica e Astronomia “Galileo Galilei”, Università degli Studi di Padova, Padova, Italy
⁶ Instituto de Astrofísica de Andalucía – CSIC, Granada, Spain

^★ Corresponding author: nair.trogolo@unc.edu.ar

Received: 11 April 2025
Accepted: 18 June 2025

Abstract

Context. The near-Earth asteroid binary system (65803) Didymos was the target of the DART (NASA) mission, which successfully tested the kinetic impact method to deflect an asteroid in September 2022. The data and images collected during the mission improved the shape model of the two components and the estimates of their physical parameters.

Aims. We improve the model for the material ejection from Didymos due to its fast spin, including the latest DART and LICIACube (ASI) data analyses, in the context of the arrival of the Hera (ESA) mission at the end of 2026.

Methods. We assessed the mass-ejection conditions from the equatorial region and explored the updated mass and volume estimates for Didymos to analyze the dynamics of the ejected particles.

Results. Particle ejection is possible in more than half of the explored parameter space. Most particles (>60%) quickly return to the primary or escape from the system (>6%). A faint disk may form up to the distance of Dimorphos and beyond, but about 10% of the centimeter-sized and larger particles may reach Dimorphos.

Conclusions. The ejection mechanism from the fast-spinning primary is one possible origin of particles that might be detected in orbit during the Hera mission rendezvous. The mass transfer from Didymos may contribute to the explanation of the boulder excess that is observed on the surface of Dimorphos.