Predictions for the Dynamical States of the Didymos System before and after the Planned DART Impact

TL;DR

This paper predicts the dynamical changes in the Didymos asteroid system resulting from NASA's DART impact, including orbital variations, shape changes, and libration effects, to inform and interpret upcoming observations from DART, Hera, and ground-based telescopes.

Contribution

It provides detailed predictions of the binary system's post-impact dynamical states, incorporating impact effects, shape changes, and orbital dynamics for the first time.

Findings

Impact will increase orbital eccentricity and tilt.

Libration amplitude of Dimorphos will be affected.

Orbital period may vary from seconds to minutes over months.

Abstract

NASA's Double Asteroid Redirection Test (DART) spacecraft is planned to impact the natural satellite of (65803) Didymos, Dimorphos, around 23:14 UTC on 26 September 2022, causing a reduction in its orbital period that will be measurable with ground-based observations. This test of kinetic impactor technology will provide the first estimate of the momentum transfer enhancement factor $\beta$ at a realistic scale, wherein ejecta from the impact provides an additional deflection to the target. Earth-based observations, the LICIACube spacecraft (to be detached from DART prior to impact), and ESA's follow-up Hera mission to launch in 2024, will provide additional characterization of the deflection test. Together Hera and DART comprise the Asteroid Impact and Deflection Assessment (AIDA) cooperation between NASA and ESA. Here the predicted dynamical states of the binary system upon arrival and after impact are presented. The assumed dynamically relaxed state of the system will be excited by the impact, leading to an increase in eccentricity and slight tilt of the orbit together with enhanced libration of Dimorphos with amplitude dependent on the currently poorly known target shape. Free rotation around the moon's long axis may also be triggered and the orbital period will experience variations from seconds to minutes over timescales of days to months. Shape change of either body due to cratering or mass wasting triggered by crater formation and ejecta may affect $\beta$ but can be constrained through additional measurements. Both BYORP and gravity tides may cause measurable orbital changes on the timescale of Hera's rendezvous.