Thermal Infrared Imager (TIRI) Simulation with Kalast for Hera Flyby Targets

Information about the formation of the Solar System and the history and geological processes of the Earth can be found studying the nature of asteroids. Understanding asteroids properties and mechanical behavior is required for planetary defense. Asteroid thermophysical properties such as thermal inertia, grain size, porosity, and surface material can be effectively constrained through thermophysical modelling combined with observations. Infrared data contributes significantly to determining reliable asteroid shapes and spin states.

Recent observations of thermal infrared imager (TIR) onboard the Hayabusa 2 spacecraft revealed the highly porous nature of the C-type asteroid Ryugu. OSIRIS-Rex infrared instruments OTES and OVIRS provided valuable information about Bennu asteroid. Both missions realized touchdown on the asteroids to collect samples and the resulting mechanical behavior from the contact could not be expected. Looking forward, the HERA mission is the next small body mission equipped with a thermal imager TIRI based on TIR with better characteristics flying towards the binary asteroid system (65803) Didymos. TIRI will be used to take images and infrared measurements of the binary asteroid Didymos. HERA is launched with two cubesats with the intention to characterize Dimorphos the moon of the binary system from a closer distance and will attempt a landing.

HERA will be launched in October 2024 and swing-by Mars in March 2025. The mission will provide a unique opportunity for calibration of the TIRI instrument and measurement of the bodies.

Here we present the simulation of those observations with Kalast, the new thermophysical model designed specifically for binary asteroids at the Royal Observatory Belgium. The tool enables in-depth analysis of thermophysical characteristics for asteroids. The model is generic for small bodies and capable of simulating binary systems, incorporating factors, such as mutual and self-heating. By utilizing shape models to accurately represent surface features, the model computes shadows for accurate illuminations. Moreover, the model simulates the thermal flux of the asteroids, considering occultation from an observer viewpoint. Roughness is being implemented to correct observed infrared flux. Whether observed through a spacecraft camera or a ground-based telescope, Kalast is capable of simulating light curves in visible and in infrared. More generally, Kalast can simulate images taken by spacecraft also in visible and infrared. Kalast is designed for the inversion of infrared measurements data obtained from thermal instruments onboard missions targeting asteroids.