[P-CG20] Future missions and instrumentation for space and planetary science

[PCG20-07] Development and operation of thermal infrared imager TIRI onboard Hera

★Invited Papers

*Naoya Sakatani¹, Tatsuaki Okada¹, Yuri Shimaki¹, Hiroki Senshu², Tomohiko Sekiguchi³, Takehiko Arai⁴, Takuya Ishizaki¹, Masanori Kanamaru⁵, Hirohide Demura⁶, Toru Kouyama⁷, Soichiro Furukawa⁵, Satoshi Tanaka¹, Joris Blommaert^8,12, Jonathan Leon Tavares⁸, Dirk Nuyts⁸, Ozgur Karatekin⁹, Gregoire Henry⁹, Luca Ruiz Lozano⁹, Gaku Nishiyama¹⁰, Thomas Mueller¹¹ (1.Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 2.Planetary Exploration Center, Chiba Institute of Technology, 3.Hokkaido University of Education, 4.Maebashi Institute of Technology, 5.University of Tokyo, 6.University of Aizu, 7.National Institute of Advanced Industrial Science and Technology, 8.VITO Remote Sensing, 9.Royal Observatory of Belgium, 10.DLR, 11.Max Planck Institute for Astrophysic, 12.Astronomy and Astrophysics Research Group, Vrije Universiteit Brussel)

Thermal infrared observation is a unique method to reveal the surface physical properties of airless planetary bodies. Surface temperature relates to the thermal conductivity, and it varies depending on the surface physical condition such as grain size, porosity, and rock abundance. JAXA have started to develop thermal imagers for planetary missions with LIR onboard Venus orbiter Akatsuki [1]. The same instrument (named TIR) was installed asteroid sample return mission Hayabusa2 [2]. Both instruments have been in operation in space for more than 10 years and are still healthy, although some degradation can be seen [3,4]. Hayabusa2 TIR revealed the porous nature of the surface boulders on C-type asteroid Ryugu [5, 6].

We have developed the next generation thermal imager TIRI [7]. TIRI is an upgrade of LIR/TIR, with higher sensitivity and resolution. Pixel number is 1024 x 768, and pixel resolution is 0.013 degrees/pix, while LIR and TIR have 328 x 248 pixels and 0.051 degrees/pix. Furthermore, TIRI is equipped with an 8-position filter wheel for multi-band imaging (1 thermal band of 8-14 μm, 6 narrow-bands, and a shutter). Our TIRI was installed on Hera spacecraft, and launched on October 2024. Soon after the launch, Earth and Moon observations were performed to check the radiometric calibration based on the ground pre-flight test. On March 2025, Hera will perform Mars flyby, during which Mars and Deimos observations are planned. Hera will visit binary asteroids Didymos-Dimorphos in 2027, and investigate them in detail after DART impact [8]. TIRI aims at investigating thermophysical properties of S-type asteroids, in comparison with those of C-type asteroid Ryugu and Bennu. Comparison of thermal properties and mid-infrared spectra between Didymos and Dimorphos will be important to investigate the formation of the binary. TIRI also contributes to understanding dynamics of the binary, orbital and rotation changes, by thermophysical modeling regarding Yarkovsky and YORP (B-YORP) effects.

In this presentation, we will focus on the development, calibration, and operation of TIRI. In addition to the ground-based calibration test, Earth, Moon, and Mars observations will be mentioned.


References: [1] Fukuhara et al. (2011) Earth, Planets, Space 63, 1009-1018. [2] Okada et al. (2017) Space Sci. Rev. 208, 255-286. [3] Taguchi et al. (2023) Earth, Planets, Space 75, 53. [4] Sakatani et al. (2024) J. Japan Soc. Infrared Sci. Tech. 34, 34-42. [5] Okada et al. (2020) Nature 579, 518-522. [6] Sakatani et al. (2021) Nature Astron. 5, 766-774. [7] Okada et al. (2024) 55th LPSC, 1777. [8] Thomas et al. (2023) Nature 616, 448-451.