10:45 〜 11:00
[MZZ40-07] The ESA Hera mission to the near-Earth asteroid binary (65803) Didymos: Documentation of the NASA DART impact and characterization of the binary system
キーワード：Planetary Defense, Asteroid, Impact, Binary Asteroid, Near-Earth Asteroid, Asteroid Deflection
The Hera mission is in development within the Space Safety Program of the European Space Agency (ESA) for launch in October 2024 with a Falcon 9 from the Space X company. After a flyby with Mars in March 2025, it will perform a rendezvous with the binary asteroid (65803) Didymos in the fall of 2026 and investigate it over 6 months.
ESA’s Hera mission, with NASA’s DART mission, will offer the first fully documented asteroid deflection test. DART successfully impacted Dimorphos, the 150 meter-sized moon of Didymos on 26 September 2022 at approximately 6.1 km/s. The DART impact resulted in a decrease of 33 minutes from the original 11 hour 55 minute orbital period of Dimorphos around Didymos. Even though determining the actual momentum transfer efficiency depends on knowledge of Dimorphos’ mass, which could not be measured from DART, an initial estimate indicates that DART’s momentum could have been multiplied by a factor more than 3 to explain the measured orbital period change.
Many questions remain about the interpretation of the DART impact outcome and for the full validation of the numerical impact models, so that they can be used with high reliability for other scenarios: (1) What is the mass of Dimorphosn which will tell us the actual DART momentum transfer efficiency? (2) What are the internal properties of Dimorphos, which have great influence on the interpretation of the outcome of the DART impact? (3) What is the final state of Dimorphos, i.e., what is the size of the crater left by the DART impact or was Dimorphos globally or in large parts reshaped by the impact? (4) What is the rotational state of Dimorphos? Did the impact put it in a tumbling state? Knowledge of both the DART impact conditions and its final outcome is the only way to to have an unbiased interpretation of the DART impact outcome and fully validate numerical impact models aimed at reproducing the impact. The Hera mission will provide answers to these important questions.
With its mother spacecraft, which carries five instruments including a thermal infrared imager contributed from JAXA, and its two cubesats, Juventas, devoted to geophysics and Milani, devoted to mineralogy and dust analysis, it will determine the outcome of the DART impact in great detail and provide measurements that have never been obtained for an asteroid so far. In particular, thanks to the low-frequency radar JuRa onboard the Juventas Cubesat, the first measurements of subsurface and internal properties of an asteroid will be performed. Moreover, Hera will also perform the first landing of a Cubesat on a body as small as Dimorphos, offering an opportunity to measure the surface mechanical response of an asteroid in its very low gravity environment.
Thanks to its detailed characterization of the binary system, Hera will also answer key questions regarding the formation of small asteroid binaries and the geophysics of small bodies. The mission development is ongoing nominally and the various working groups of the Hera Science Team are working intensively, adjusting their investigations to account for the new and important knowledge provided by DART and LICIAcube data, to support this development and be best prepared for the surprises that Hera will offer during its visit to Didymos in late 2026-2027.
Acknowledgment: P.M. acknowledges funding support from ESA and CNES
ESA’s Hera mission, with NASA’s DART mission, will offer the first fully documented asteroid deflection test. DART successfully impacted Dimorphos, the 150 meter-sized moon of Didymos on 26 September 2022 at approximately 6.1 km/s. The DART impact resulted in a decrease of 33 minutes from the original 11 hour 55 minute orbital period of Dimorphos around Didymos. Even though determining the actual momentum transfer efficiency depends on knowledge of Dimorphos’ mass, which could not be measured from DART, an initial estimate indicates that DART’s momentum could have been multiplied by a factor more than 3 to explain the measured orbital period change.
Many questions remain about the interpretation of the DART impact outcome and for the full validation of the numerical impact models, so that they can be used with high reliability for other scenarios: (1) What is the mass of Dimorphosn which will tell us the actual DART momentum transfer efficiency? (2) What are the internal properties of Dimorphos, which have great influence on the interpretation of the outcome of the DART impact? (3) What is the final state of Dimorphos, i.e., what is the size of the crater left by the DART impact or was Dimorphos globally or in large parts reshaped by the impact? (4) What is the rotational state of Dimorphos? Did the impact put it in a tumbling state? Knowledge of both the DART impact conditions and its final outcome is the only way to to have an unbiased interpretation of the DART impact outcome and fully validate numerical impact models aimed at reproducing the impact. The Hera mission will provide answers to these important questions.
With its mother spacecraft, which carries five instruments including a thermal infrared imager contributed from JAXA, and its two cubesats, Juventas, devoted to geophysics and Milani, devoted to mineralogy and dust analysis, it will determine the outcome of the DART impact in great detail and provide measurements that have never been obtained for an asteroid so far. In particular, thanks to the low-frequency radar JuRa onboard the Juventas Cubesat, the first measurements of subsurface and internal properties of an asteroid will be performed. Moreover, Hera will also perform the first landing of a Cubesat on a body as small as Dimorphos, offering an opportunity to measure the surface mechanical response of an asteroid in its very low gravity environment.
Thanks to its detailed characterization of the binary system, Hera will also answer key questions regarding the formation of small asteroid binaries and the geophysics of small bodies. The mission development is ongoing nominally and the various working groups of the Hera Science Team are working intensively, adjusting their investigations to account for the new and important knowledge provided by DART and LICIAcube data, to support this development and be best prepared for the surprises that Hera will offer during its visit to Didymos in late 2026-2027.
Acknowledgment: P.M. acknowledges funding support from ESA and CNES