2,3,4,4,5,6,7,8,7,5,5,- 1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
- 2Department of Aerospace Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
- 3Trans Tasman Occultation Alliance & International Occultation Timing Association (IOTA), Wellington PO Box 3181, New Zealand
- 4Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA
- 5Department of Physics, Aristotle University of Thessaloniki, Greece;
- 6LESIA, Observatoire de Paris—Section Meudon, F-92195 Meudon Cedex, France;
- 7Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, F-06304 NICE Cedex 4, France
- 8naXys, Department of Mathematics, University of Namur, Rue de Bruxelles 61, B-5000 Namur, Belgium
- 9LTE, Observatoire de Paris, Universit\'e PSL, CNRS, Sorbonne Universit\'e, Paris, France
The Double Asteroid Redirection Test (DART) mission was a successful planetary defense demonstration of a kinetic impactor on Dimorphos, the satellite of binary near-Earth asteroid 63803 Didymos (Daly et al. 2023). The DART impact changed not only the orbit of the satellite Dimorphos about Didymos (Thomas et al. 2023), but also the orbit of the Didymos system about the Sun (Makadia et al. 2024). We report quantitative results of this heliocentric deflection, leading to a revised estimate of the momentum enhancement factor β as well as an estimate of the bulk density ρ of the target Dimorphos.
In the months following the DART impact, a series of stellar occultation campaigns led to a total of 18 observed occultations of the Didymos system from 2022-Oct-15 to 2023-Jan-22. These observations represent an exquisite astrometric data set, with reported errors of no more than a few milliarcseconds. Three of these observations were reported with <1 mas uncertainty, and the lowest reported uncertainty was 0.2 mas on 2023-Jan-22. With these measurements, the estimate of the Yarkovsky effect on Didymos became significantly more refined compared to the pre-impact estimates, but the effect of the DART deflection was not yet plainly discernible.
However, in May 2024–March 2025, observers detected four additional stellar occultations by Didymos. With this additional data, we estimate the change in velocity in the heliocentric along-track direction to be ∆V = -11.7 ± 1.3 μm/s. Given the known circumstances of the DART impact, this deflection implies β = 2.0 ± 0.3, which is consistent with, but somewhat lower than, previous reports (Cheng et al. 2023). A lower value of β implies a lower bulk density ρ of Dimorphos, and indeed, using the measured deflection of the Dimorphos orbit around Didymos (Naidu et al. 2024), we estimate ρ = 1.54 ± 0.22 g/cm3, indicating that Dimorphos is significantly under-dense with respect to Didymos.
How to cite: Chesley, S. R., Makadia, R., Herald, D., Farnocchia, D., Chabot, N. L., Naidu, S. P., Rivkin, A. S., Siakas, A., Souami, D., Tanga, P., Tsavdaridis, S., Tsiganis, K., Bouquillon, S., and Eggl, S.: First detection of an asteroid’s heliocentric deflection: The Didymos system after DART, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–12 Sep 2025, EPSC-DPS2025-1331, https://doi.org/10.5194/epsc-dps2025-1331, 2025.
