Speaker
Description
The analysis of mm-wavelength thermal emission from near-Earth asteroids can be used to constrain thermophysical (thermal inertia, emissivity) and radiative (index of refraction, loss tangent) properties of the top few centimeters of regolith. These properties can be used to constrain the regolith porosity. For near-Earth asteroids (NEAs), regolith porosity is one of the physical properties that must be known for the development of impact risk mitigation missions [1].
Here we present a framework, based on [2], that combines thermal, radiative transfer, and regolith thermophysical models that can be compared to observed passive mm-wave thermal emission from ground observations. The thermal model used is KRC [3], the radiative transfer model is that used by [2], and the regolith thermophysical model is based on [4].
This approach requires a priori knowledge of the object’s composition, Bond albedo, shape, size, orbit, and spin properties. Comparisons of outputs from the series of models to observations provide best-fit estimates of thermal inertia, index of refraction, loss tangent, and effective emissivity. These best-fit solutions are then used to estimate surficial density, porosity, and effective grain size.
The first observations from a recent thermal survey of NEAs, aimed at acquiring data from up to 15 targets per year using mm and sub-mm facilities (ALMA, IRAM, SMA, VLA), are now available for analysis. Observations of targets acquired include (1685) Toro, 2005 EK70, 2015 DE198, 2013 NK4, 2011 UL21, 2024 ON, (1036) Ganymede, (4954) Eric, and 2006 WB. Archival observations of Dimorphos/Didymos and 1998 QE2 are also available. Observations of these objects provide an opportunity to demonstrate the thermophysical-radiative transfer modeling approach to determine regolith porosities of NEAs. Results will be presented at the conference.
Acknowledgements and disclaimers:
This research program is supported through NASA ROSES Near-Earth Object Observations program grant 23-YORPD23_2-0034. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
References:
[1] Levasseur-Regourd, A., Chantal, Hadamcik, E., Lasue, J., 2006, Advances in Space Research, 37(1), p. 161–168.
[2] Li, J-Y, Moullet, A, Titus, T, N., Hsieh, H. H., Sykes, M. V., 2020, Disk-integrated Thermal Properties of Ceres Measured at Millimeter Wavelengths, The Astronomical Journal, 159(5), id.215, 9 p.
[3] Kieffer, H., 2013, Thermal model for analysis of Mars infrared mapping, Journal of Geophysical Research: Planets, 118(3), pp. 451–470.
[4] MacLennan, E., & Emery, J., 2022, Thermophysical Investigation of Asteroid Surfaces. II. Factors Influencing Grain Size, Planet. Sci. J.,3(2), 47 p. 47.