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The ESA Hera mission to the near-Earth asteroid binary (65803) Didymos: Documentation of the NASA DART impact and full characterization of the asteroid system

Presentation #201.07 in the session Future Missions, Instrumentations and Facilities - Part 1 (Oral Presentation)

Published onOct 23, 2023
The ESA Hera mission to the near-Earth asteroid binary (65803) Didymos: Documentation of the NASA DART impact and full characterization of the asteroid system

The Hera mission is in development within the ESA Space Safety Program for launch in October 2024 with a Falcon 9 rocket. It will perform a rendezvous with the binary asteroid (65803) Didymos in early 2027 and investigate it over 6 months [1]. Together with the NASA DART mission [2], Hera will contribute to the first asteroid deflection test.

DART successfully impacted Dimorphos, the 150 m-sized moon of Didymos [3]. The DART impact resulted in a decrease of 33mn from the initial 11h55mn orbital period of Dimorphos around Didymos [4]. Although DART was extremely successful, many questions remain open about the interpretation of its outcome and the full validation of the numerical impact models: (1) What is Dimorphos’ mass? Mass is needed for an actual determination of DART momentum transfer efficiency [5]. (2) Is Dimorphos a monolith covered with gravel and boulders or, as currently assumed, an aggregate? This has great influence on the DART impact outcome interpretation. (3) What is Dimorphos’ final state, i.e., what is the size of the crater left by the DART impact or was Dimorphos globally or in large parts reshaped? (4) What is the final binary system’s dynamical state? All this knowledge is crucial to fully validate impact models and to have an unbiased interpretation of the DART impact outcome. Other questions relate to the thermal and mineralogical properties as well as the potential presence of dust in the close environment of the binary system.

Answering these questions is the goal of Hera that will perform the first asteroid binary rendezvous. Hera will also answer key questions regarding the formation of small asteroid binaries and small body geophysics in general.

The spacecraft carries 5 instruments including 2 framing cameras, a hyperspectral imager, a laser altimeter, a thermal-IR imager from JAXA, and 2 Cubesats: Juventas, dedicated to asteroid geophysics, including direct measurements of internal properties for the first time, and Milani, dedicated to mineralogy and dust investigation. Hera will also perform the first Cubesat landing on such a small body, providing information on the surface mechanical response in its very low gravity environment.

The development is ongoing nominally and the working groups of the Hera Science Team are working intensively, adjusting their investigations to account for the new and important results provided by DART and LICIAcube data.

Acknowledgments: We thank ESA and CNES for support.

References: [1] Michel P. et al. (2022) PSJ, 3, 160. [2] Rivkin A. et al. (2021) PSJ, 2, 173. [3] Dally, R. T. et al. (2023) Nature. [4] Thomas C. et al. (2023) Nature. [5] Cheng A. et al. (2023) Nature.

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