(25143) Itokawa: The Power of Radiometric Techniques for the Interpretation of Remote Thermal Observations in the Light of the Hayabusa Rendezvous Results

Abstract

The near-Earth asteroid (25143) Itokawa was characterised in great detail by the Japanese Hayabusa mission. We revisited the available thermal observations in the light of the true asteroid properties with the goal to evaluate the possibilities and limitations of thermal model techniques. In total, we used 25 published ground-based mid-infrared photometric observations and 5 so far unpublished measurements from the Japanese infrared astronomical satellite AKARI in combination with improved H-G values. Our thermophysical model (TPM) approach allowed us to determine correctly the sense of rotation, to estimate the thermal inertia and to derive robust effective size and albedo values by only using a simple spherical shape model. A more complex shape model, derived from light-curve inversion techniques, improved the quality of the predictions considerably and made the interpretation of thermal light-curve possible. The radiometrically derived effective diameter value agrees within 2% of the true Itokawa size value. The combination of our TPM and the final Itokawa in-situ shape model was then used as a benchmark for deriving and testing radiometric solutions. The consolidated value for the surface-averaged thermal inertia is 700 $\pm$ 200 Jm${}^{-2}$s${}^{-0.5}$K${}^{-1}$. We found that even the high resolution shape models still require additional small-scale roughness in order to explain the disk-integrated infrared measurements. Our description of the thermal effects as a function of wavelengths, phase angle, and rotational phase facilitates the planning of crucial thermal observations for sophisticated characterization of small bodies, including other potentially hazardous asteroids. Our analysis shows the power of radiometric techniques to derive the size, albedo, thermal inertia, and also spin-axis orientation from small sets of measurements at thermal infrared wavelengths.

Accepted for publication in PASJ, 30 pages, 9 figures, 4 tables

References in corpus (1)

• Thermal inertia of near-Earth asteroids and implications for the magnitude of the Yarkovsky effect

Cited by in corpus (13)

• Hayabusa-2 Mission Target Asteroid 162173 Ryugu (1999 JU3): Searching for the Object's Spin-Axis Orientation
• Thermophysical modeling of asteroids from WISE thermal infrared data - Significance of the shape model and the pole orientation uncertainties
• Spin states of asteroids in the Eos collisional family
• Photometric survey, modelling, and scaling of long-period and low-amplitude asteroids
• Constraining the Thermal Properties of Planetary Surfaces using Machine Learning: Application to Airless Bodies
• The Global Surface Roughness of 25143 Itokawa
• The fast spin of near-Earth asteroid (455213) 2001 OE84, revisited after 14 years: constraints on internal structure
• A Comparative Study of Infrared Asteroid Surveys: IRAS, AKARI, and WISE
• Follow-up observations for the Asteroid Catalog using AKARI Spectroscopic Observations
• Large Halloween Asteroid at Lunar Distance
• Observed asteroid surface area in the thermal infrared
• ASTERIA -- Thermal Inertia Evaluation of asteroid Didymos
• A 3D thermophysical model for binary asteroid systems: Application to the BYORP effect on (175706) 1996 FG3