5:15 PM - 6:45 PM
[PPS03-P01] Thermal Imaging of Small Solar System Bodies: Ryugu, Didymos Binary and Apophis
Keywords:thermal infrared imager, thermography, thermal inertia, thermophysical model
Introduction:
Thermal infrared imaging of Earth-approaching asteroids from spacecraft is a useful method to characterize the targets during flyby and rendezvous missions. We present here instruments, the past results and the future prospects related to Planetary Defense.
Thermal Imager TIR onboard Hayabusa2:
On Hayabusa2, a thermal infrared imager TIR is one of remote sensing instruments to investigate thermophysical properties of C-type Near-Earth asteroid 162173 Ryugu. TIR is a single band thermal imager that covers 8-12 µm in wavelength, with the FOV of 16.7° x 12.7°, detected by an uncooled bolometer array of 328 x 248 effective pixels [1]. TIR successfully imaged the entire surface of Ryugu by the asteroid rotation from Home Position, 20 km from the asteroid, deriving the thermal inertia and roughness maps simultaneously. During the close-up thermal images at low altitude, individual boulders were imaged, to find the colder boulders (Cold Spots) or hotter boulders (Hot Spots) compared with their surroundings. The derived thermal inertia was typically 200-400 J kg-1 m-2 s-0.5 (hereafter, tiu), which is much lower than that of carbonaceous chondrites (600-1000 tiu). Laboratory thermal diffusivity measurements of Ryugu returned samples show that their thermal inertia are ~1000 tiu, similar to that of primitive volatile-rich meteorites like CI chondrites or Tagish Lake meteorites, but sometimes < 500 tiu if internal cracks exist. The Ryugu materials seems to be similar to CI chondrites but with many pores and cracks for a boulder scale.
TIR for Hayabusa2#:
During the extended mission called Hayabusa2#, TIR will take thermal images of S-type Near-Earth asteroid 2001CC21 during flyby in 2026, to determine the typical thermal inertia, spin direction, and shape modeling including the night side regions. The final destination of Hayabusa2# will be a very small (~30 m diameter) Near-Earth asteroid 1998KY26, which will become the smallest asteroid ever explored by a spacecraft. Such small asteroids are significantly important to be investigated as potentially hazardous bodies in the near future, especially whether such a small-sized asteroid is a monolithic or a rubble-pile body, and how it formed and evolved.
Thermal Imager TIRI onboard Hera:
A thermal infrared imager TIRI is being prepared for the ESA Hera mission to the near-Earth S-type asteroid binary 65803 Didymos and its moon Dimorphos, which will be launched in October 2024 and rendezvous with the asteroid binary in December 2026. Hera will observe the binary asteroids, after the kinetic impact of the NASA DART spacecraft to Dimorphos, to validate the effect of impact deflection and TIRI will contribute to part of the role, especially for the surface porosity, composition, thermal modeling (non-gravitational acceleration), and detailed asteroid shape including the night side images.
TIRI is a light-weighted, thermal infrared imager based on an uncooled bolometer array of 1024 x 768 pixels, with the FOV of 13.3° x 10.0°. TIRI has the wavelength range of 8-14 µm for wide band, with six narrow bands centered at 7.8, 8.6, 9.6, 10.6, 11.6, and 13.0µm, to investigate the thermophysical properties and composition of the asteroids [2].
Thermal Imager TIRI for RAMSES:
TIRI will be also used for the RAMSES which is the ESA-led mission under study to rendezvous with 99942 Apophis a few months before its close encounter to Earth in April 2029, and the pre-/during-/post- observations of the asteroid surface and interior will be carried out to study what happens by the tidal forces by Earth. TIRI will determine thermal inertia, composition of the asteroid, and possibly the surface movement.
References: [1] Okada T. et al. (2017) SSR. 208, 255-286. [2] Okada, T. et al. (2024) LPSC 2024, #1777.
Thermal infrared imaging of Earth-approaching asteroids from spacecraft is a useful method to characterize the targets during flyby and rendezvous missions. We present here instruments, the past results and the future prospects related to Planetary Defense.
Thermal Imager TIR onboard Hayabusa2:
On Hayabusa2, a thermal infrared imager TIR is one of remote sensing instruments to investigate thermophysical properties of C-type Near-Earth asteroid 162173 Ryugu. TIR is a single band thermal imager that covers 8-12 µm in wavelength, with the FOV of 16.7° x 12.7°, detected by an uncooled bolometer array of 328 x 248 effective pixels [1]. TIR successfully imaged the entire surface of Ryugu by the asteroid rotation from Home Position, 20 km from the asteroid, deriving the thermal inertia and roughness maps simultaneously. During the close-up thermal images at low altitude, individual boulders were imaged, to find the colder boulders (Cold Spots) or hotter boulders (Hot Spots) compared with their surroundings. The derived thermal inertia was typically 200-400 J kg-1 m-2 s-0.5 (hereafter, tiu), which is much lower than that of carbonaceous chondrites (600-1000 tiu). Laboratory thermal diffusivity measurements of Ryugu returned samples show that their thermal inertia are ~1000 tiu, similar to that of primitive volatile-rich meteorites like CI chondrites or Tagish Lake meteorites, but sometimes < 500 tiu if internal cracks exist. The Ryugu materials seems to be similar to CI chondrites but with many pores and cracks for a boulder scale.
TIR for Hayabusa2#:
During the extended mission called Hayabusa2#, TIR will take thermal images of S-type Near-Earth asteroid 2001CC21 during flyby in 2026, to determine the typical thermal inertia, spin direction, and shape modeling including the night side regions. The final destination of Hayabusa2# will be a very small (~30 m diameter) Near-Earth asteroid 1998KY26, which will become the smallest asteroid ever explored by a spacecraft. Such small asteroids are significantly important to be investigated as potentially hazardous bodies in the near future, especially whether such a small-sized asteroid is a monolithic or a rubble-pile body, and how it formed and evolved.
Thermal Imager TIRI onboard Hera:
A thermal infrared imager TIRI is being prepared for the ESA Hera mission to the near-Earth S-type asteroid binary 65803 Didymos and its moon Dimorphos, which will be launched in October 2024 and rendezvous with the asteroid binary in December 2026. Hera will observe the binary asteroids, after the kinetic impact of the NASA DART spacecraft to Dimorphos, to validate the effect of impact deflection and TIRI will contribute to part of the role, especially for the surface porosity, composition, thermal modeling (non-gravitational acceleration), and detailed asteroid shape including the night side images.
TIRI is a light-weighted, thermal infrared imager based on an uncooled bolometer array of 1024 x 768 pixels, with the FOV of 13.3° x 10.0°. TIRI has the wavelength range of 8-14 µm for wide band, with six narrow bands centered at 7.8, 8.6, 9.6, 10.6, 11.6, and 13.0µm, to investigate the thermophysical properties and composition of the asteroids [2].
Thermal Imager TIRI for RAMSES:
TIRI will be also used for the RAMSES which is the ESA-led mission under study to rendezvous with 99942 Apophis a few months before its close encounter to Earth in April 2029, and the pre-/during-/post- observations of the asteroid surface and interior will be carried out to study what happens by the tidal forces by Earth. TIRI will determine thermal inertia, composition of the asteroid, and possibly the surface movement.
References: [1] Okada T. et al. (2017) SSR. 208, 255-286. [2] Okada, T. et al. (2024) LPSC 2024, #1777.