14:30 〜 14:45
[MZZ40-04] Thermal Imaging for Planetary Defense Missions: Hayabusa2#, Hera, and RAMSES
キーワード：プラネタリ―ディフェンス、熱赤外カメラ、サーモグラフィ、熱物理モデル、熱慣性
Introduction:
Planetary defense is the activity to prevent natural disasters caused by asteroid impact to Earth, which people worldwide are getting aware of by the Chelyabinsk event in 2013, the kinetic impact of the NASA Double Asteroid Redirect Test (DART) to asteroid Dimorphos in 2022, the close encounter to Earth of the asteroid Apophis in 2029, and the recent discovery of asteroid 2024YR4 potentially impacting Earth in 2032. Physical properties of asteroids are essential for planetary defense study on investigating the nature of asteroids, the effect of asteroid deflection by a kinetic impact of spacecraft, and a degree of disaster caused by an asteroid impact to Earth. Thermal infrared imaging of asteroids from spacecraft is a useful method to characterize the targets during flyby and rendezvous to provide their thermophysical and compositional properties. Here we present the instruments, results and future observation plans in Hayabusa2#, Hera and RAMSES missions.
Thermal Imager TIR onboard Hayabusa2#:
A thermal infrared imager TIR on Hayabusa2 [1] is developed to investigate thermophysical properties of C-type Near-Earth asteroid 162173 Ryugu, and two more asteroids in the extended mission Hayabusa2#, S-type asteroid 98943 Torifune in 2026 and X-type 1998KY26 in 2031 [2]. TIR is a single band thermal imager based on an uncooled micro bolometer (NEC320A) and covers 8-12 µm in wavelength, with the FOV of 16.7° x 12.7° and the IFOV of 0.88 mrad/pixel (328 x 248 effective pixels). Its sensor unit is inherited from Akatsuki LIR [3]. With TIR, one-rotation thermal images of Ryugu have been taken, obtaining the global map of thermal inertia and roughness [4,5]. Close-up thermal images taken at lower altitudes have shown individual boulders, to find a variety of boulders: including colder boulders (Cold Spots) and hotter boulders (Hot Spots) [4,6]. TIR will observe two more asteroids, and the final destination will become the smallest asteroid ever explored by a spacecraft, which is interested to know whether they are monolithic or rubble-pile and how they formed and evolved.
Thermal Imager onboard Hera and RAMSES:
A thermal infrared imager TIRI [7,8] is developed for the ESA Hera mission [9] to investigate S-type asteroid binary 65803 Didymos and its moon Dimorphos, the target of kinetic impact of DART [10] in 2026-2027 to characterize the asteroid in physical and chemical properties, as well as to investigate the effect of impact deflection. It is also used for ESA-led RAMSES (Rapid Apophis Mission for Space Safety) mission to observe the S-type asteroid 99942 Apophis before, during, and after its Earth close encounter on 13 April 2029, to discover the changes caused by terrestrial tidal forces, which is the once-in-a-millennium opportunity to understand the internal structure and physical strength by a space mission. TIRI is a light-weighted (3.92 kg) instrument based on an uncooled bolometer array (Lynred PICO 1024 gen2) of 1024 x 768 pixels, with the field of view of 13.0° x 9.9°, corresponding to IFOV of 0.013° per pixel (0.23 mrad per pixel). It covers the temperature range of -120 to 150 ℃ and the wavelength range of 8-14 µm for the wide band, with six narrow bands centered at 7.8, 8.6, 9.6, 10.6, 11.6, and 13.0µm. TIRI will reveal the thermophysical properties and composition of asteroids.
References: [1] Okada T. et al. (2017) SSR. 208, 255-286. [2] Hirabayashi M. et al. (2021) ASR 68, 1533. [3] Fukuhara, T. et al. (2011), EPS 63, 1009. [4] Okada T. et al. (2020) Nature 579, 518. [5] Shimaki Y. et al. (2020) Icarus 113835. [6] Sakatani N. et al. (2021) Nat. Astron. 5, 766. [7] Okada T. et al. (2024) Planetary People, 33, 220. [8] Okada T. (2025) LPSC, #1965. [9] Michel P. et al. (2022) PSJ 3, 160. [10] e.g., Rivkin A. S. and Cheng A. F. (2023) Nat. Commun. 14, 1003.
Planetary defense is the activity to prevent natural disasters caused by asteroid impact to Earth, which people worldwide are getting aware of by the Chelyabinsk event in 2013, the kinetic impact of the NASA Double Asteroid Redirect Test (DART) to asteroid Dimorphos in 2022, the close encounter to Earth of the asteroid Apophis in 2029, and the recent discovery of asteroid 2024YR4 potentially impacting Earth in 2032. Physical properties of asteroids are essential for planetary defense study on investigating the nature of asteroids, the effect of asteroid deflection by a kinetic impact of spacecraft, and a degree of disaster caused by an asteroid impact to Earth. Thermal infrared imaging of asteroids from spacecraft is a useful method to characterize the targets during flyby and rendezvous to provide their thermophysical and compositional properties. Here we present the instruments, results and future observation plans in Hayabusa2#, Hera and RAMSES missions.
Thermal Imager TIR onboard Hayabusa2#:
A thermal infrared imager TIR on Hayabusa2 [1] is developed to investigate thermophysical properties of C-type Near-Earth asteroid 162173 Ryugu, and two more asteroids in the extended mission Hayabusa2#, S-type asteroid 98943 Torifune in 2026 and X-type 1998KY26 in 2031 [2]. TIR is a single band thermal imager based on an uncooled micro bolometer (NEC320A) and covers 8-12 µm in wavelength, with the FOV of 16.7° x 12.7° and the IFOV of 0.88 mrad/pixel (328 x 248 effective pixels). Its sensor unit is inherited from Akatsuki LIR [3]. With TIR, one-rotation thermal images of Ryugu have been taken, obtaining the global map of thermal inertia and roughness [4,5]. Close-up thermal images taken at lower altitudes have shown individual boulders, to find a variety of boulders: including colder boulders (Cold Spots) and hotter boulders (Hot Spots) [4,6]. TIR will observe two more asteroids, and the final destination will become the smallest asteroid ever explored by a spacecraft, which is interested to know whether they are monolithic or rubble-pile and how they formed and evolved.
Thermal Imager onboard Hera and RAMSES:
A thermal infrared imager TIRI [7,8] is developed for the ESA Hera mission [9] to investigate S-type asteroid binary 65803 Didymos and its moon Dimorphos, the target of kinetic impact of DART [10] in 2026-2027 to characterize the asteroid in physical and chemical properties, as well as to investigate the effect of impact deflection. It is also used for ESA-led RAMSES (Rapid Apophis Mission for Space Safety) mission to observe the S-type asteroid 99942 Apophis before, during, and after its Earth close encounter on 13 April 2029, to discover the changes caused by terrestrial tidal forces, which is the once-in-a-millennium opportunity to understand the internal structure and physical strength by a space mission. TIRI is a light-weighted (3.92 kg) instrument based on an uncooled bolometer array (Lynred PICO 1024 gen2) of 1024 x 768 pixels, with the field of view of 13.0° x 9.9°, corresponding to IFOV of 0.013° per pixel (0.23 mrad per pixel). It covers the temperature range of -120 to 150 ℃ and the wavelength range of 8-14 µm for the wide band, with six narrow bands centered at 7.8, 8.6, 9.6, 10.6, 11.6, and 13.0µm. TIRI will reveal the thermophysical properties and composition of asteroids.
References: [1] Okada T. et al. (2017) SSR. 208, 255-286. [2] Hirabayashi M. et al. (2021) ASR 68, 1533. [3] Fukuhara, T. et al. (2011), EPS 63, 1009. [4] Okada T. et al. (2020) Nature 579, 518. [5] Shimaki Y. et al. (2020) Icarus 113835. [6] Sakatani N. et al. (2021) Nat. Astron. 5, 766. [7] Okada T. et al. (2024) Planetary People, 33, 220. [8] Okada T. (2025) LPSC, #1965. [9] Michel P. et al. (2022) PSJ 3, 160. [10] e.g., Rivkin A. S. and Cheng A. F. (2023) Nat. Commun. 14, 1003.