Approach to understand of the processes of planetary formation and evolution
The Hera expedition is a unique and valuable opportunity not only as a technological demonstration but also to advance our understanding of the processes of planetary formation and evolution.
Asteroid exploration is a specialization in which Japan leads the world. The explorer will be equipped with a thermal infrared camera, which has been proven in Hayabusa2, and will contribute greatly to the science of impact phenomena, asteroid geology, dynamics, and thermophysical properties.
Hera's Goals
Comparisons will be made between the asteroids of different sizes, the double asteroids Didymos (about 780 meters in diameter) and its satellite Dimorphos (about 160 meters in diameter), as well as the C-type asteroid Ryugu visited by Hayabusa2, the B-type asteroid Bennu visited by NASA’s Osiris Rex and S-type asteroid Didymos to confirm for the first time the differences in physical properties of asteroids due to differences in object size and spectral type.
New findings are also expected on the characteristics of dynamical evolution in binary asteroids and progress in understanding collision phenomena in small asteroids, which are expected to provide clues to the mysteries of planet formation and evolution.
New technologies to be implemented primarily by ESA include small and autonomous communication link observations with CubeSats and autonomous optical image navigation using thermal infrared are also being considered.
Thermal infrared camera
TIRI (Thermal InfraRed Imager)
What can be understood by thermal imaging?
Thermal imaging of celestial objects provides information on surface physical conditions.
For example, if the surface physical state (e.g., porosity) of primordial bodies is known, it will be possible to elucidate the strength, impact propagation, and destruction phenomena at the time of celestial impact.
Observations by the Hayabusa2’s onboard thermal infrared camera, the TIR, were very useful in selecting a landing site by taking global thermal images to obtain daily temperature variations. In the thermal inertia map, we found that the surface layer of C-type asteroid Ryugu is covered with low thermal inertia (possibly high porosity) rocks. [Okada+2020, Nature; Shimaki+2020, Icarus].
By imaging the night side, which is invisible in visible light, we were also able to create a complete shape model.
Local thermal imaging has revealed the thermophysical properties of individual rock fragments and blocks, so that high and low temperature spots were discovered [Okada+, Nature 2020; Sakatani+, Nature Astron. 2021], as well as information on the characteristic topography of the surface layer, even 10cm-sized target markers were detected.
The newly developed TIRI improved sensitivity and resolution compared with TIR and also adds multi-wavelength spectroscopy that will allow it to make a significant contribution to both planetary science and planetary defense, especially in understanding the physical properties and formation processes of the Didymos binary asteroid system.
TIRI's Challenge
Increased sensitivity and resolution
By improving the sensitivity and resolution of the infrared camera, more detailed thermophysical property information will be acquired to clarify the surface physical state. Furthermore, the introduction of thermal infrared imagery navigation is also being studied in the Hera project.
Introduction of multicolor spectral imaging (6-bands)
Compositional information is acquired through the introduction of multicolor spectral imaging (6 bands). This will further clarify differences by location, such as between Didymos and Dimorphos, inside and outside of craters caused by the DART collision, comparisons with ejecta, and differences between flatlands (sediments) and rocks.
TIRI's Goal
Planetary Science
Investigation of thermophysical properties of S-type asteroids.
Investigation of thermophysical properties of 100m-class asteroids and elucidation of the formation process of binary asteroids.
Exploring binary system dynamics and thermal effects (BYORU).
Investigation of traces and effects of DART collision experiments and scaling laws.
Investigation of the effect of surface layer grain size on space weathering.
Planetary Defense
Investigation of porosity and strength of DART target asteroids.
Investigation of binary system dynamics and collision anomalies.
Investigation of shape, size and material of DART impact crater.
Investigation of deposition state on Didymos of DART collision ejector.
Contribution to optical self-contained navigation using thermal infrared images.
Thermal infrared imaging is a very useful tool for planetary explorations!
Other Mission Payloads
AFC (Asteroid Framing Camera)
Visible Camera
HS-H
(HyperScout-H)
Multicolor camera
PALT (Planetary ALTimeter)
Laser Altimeter
RADIOSCIENCE
Radio science
Juventas
CubeSat
Milani
CubeSat
Mission Payloads (All in +Z directions)
Spacecraft Configuration
