Thermophysical modeling of main-belt asteroids from WISE thermal data

Abstract

By means of a varied-shape thermophysical model of Hanuš et al. (2015, Icarus, Volume 256) that takes into account asteroid shape and pole uncertainties, we analyze the thermal infrared data acquired by the NASA's Wide-field Infrared Survey Explorer of about 300 asteroids with derived convex shape models. We utilize publicly available convex shape models and rotation states as input for the thermophysical modeling. For more than one hundred asteroids, the thermophysical modeling gives us an acceptable fit to the thermal infrared data allowing us to report their thermophysical properties such as size, thermal inertia, surface roughness or visible geometric albedo. This work more than doubles the number of asteroids with determined thermophysical properties, especially the thermal inertia. In the remaining cases, the shape model and pole orientation uncertainties, specific rotation or thermophysical properties, poor thermal infrared data or their coverage prevent the determination of reliable thermophysical properties. Finally, we present the main results of the statistical study of derived thermophysical parameters within the whole population of main-belt asteroids and within few asteroid families. Our sizes based on TPM are, in average, consistent with the radiometric sizes reported by Mainzer et al. (2016, NASA PDS, Volume 247). The thermal inertia increases with decreasing size, but a large range of thermal inertia values is observed within the similar size ranges between D∼10-100 km. We derived unexpectedly low thermal inertias (<20 J m −2 s −1/2 K −1 ) for several asteroids with sizes 10 < D < 50 km, indicating a very fine and mature regolith on these small bodies. The thermal inertia values seem to be consistent within several collisional families, however, the statistical sample is in all cases rather small. The fast rotators with rotation period P 4 hours tend to have slightly larger thermal inertia values, so probably do not have a fine regolith on the surface. This could be explained, for example, by the loss of the fine regolith due to the centrifugal force, or by the ineffectiveness of the regolith production (e.g., by the thermal cracking mechanism of Delbo' et al. 2014, Nature, Issue 508).

Ancient and primordial collisional families as the main sources of X-type asteroids of the inner main belt

“…For the age determination, we thus assume that the probability function of the density of family members is a Gaussian function centred at 3,500 kg m −3 and with σ = 450 kg m −3 . The asteroid (757) Portlandia, with a spherical equivalent diameter of about 33 km, is at the moment of writing the only family member with known thermal inertia value (Γ) around 60 J m −2 s −0.5 K −1 (Hanuš et al 2018). The other non-family X-complex asteroids with 0.1 < p V < 0.3 with measured thermal inertia values are (272) Antonia, (413) Edburga, (731) Sorga, (789) Lena, (857) Glasenappia, and (1013) Tombecka with values of 75, 110, 62, 47, 47, and 55 J m −2 s −0.5 K −1 , which were measured at heliocentric distances (r h ) of 2.9, 2.9, 3.3, 2.7,2.3, and 3.1 au, respectively (Hanuš et al 2018).…”

“…The asteroid (757) Portlandia, with a spherical equivalent diameter of about 33 km, is at the moment of writing the only family member with known thermal inertia value (Γ) around 60 J m −2 s −0.5 K −1 (Hanuš et al 2018). The other non-family X-complex asteroids with 0.1 < p V < 0.3 with measured thermal inertia values are (272) Antonia, (413) Edburga, (731) Sorga, (789) Lena, (857) Glasenappia, and (1013) Tombecka with values of 75, 110, 62, 47, 47, and 55 J m −2 s −0.5 K −1 , which were measured at heliocentric distances (r h ) of 2.9, 2.9, 3.3, 2.7,2.3, and 3.1 au, respectively (Hanuš et al 2018). Since thermal inertia is temperature dependent (Rozitis et al 2018) and the surface temperature of an asteroid is a function of its heliocentric distance, we correct these thermal inertia values to 2.38 au assuming that Γ ∝ r −3/4 h (Delbo et al 2015).…”

Thermal properties of slowly rotating asteroids: results from a targeted survey

“…12) The above-mentioned trend was found on the values derived from estimated beaming parameters using a simplified approach. Recent results from TPM by Hanuš et al (2018b) showed a rather large diversity of thermal inertia values for slow rotators within the size range of 10-100 km. Here we further investigate this issue by studying more slow rotators in both visible light and thermal infrared radiation.…”

Thermophysical Modeling of Asteroid Surfaces Using Ellipsoid Shape Models

“…Data collected which have large wavelength separation that span the blackbody peak are most useful, since they are sensitive to relatively warmer and cooler portions of the surface -in other words the overall temperature distribution. Delbo' and Tanga (2009) estimated thermal inertias for 10 main-belt asteroids using multi-wavelength IRAS (Infrared Astronomical Satellite) observations, and Hanus et al (2015Hanus et al ( , 2018 collectively present thermal inertia estimates for 131 objects using WISE (Wide-Field infrared Survey Explorer) data. Harris and Drube (2016) present population trends using over a hundred thermal inertias derived from the NEATM η values of asteroid observed with WISE.…”

“…The general purpose of a thermal model is to compute surface temperatures for an object, which are in turn used to calculate the emitted flux at the desired wavelengths (see , for a recent review). Thermophysical models have proved to be a powerful tool in providing meaningful estimates of an object's size and albedo and provide insight into thermophysical characteristics of asteroid regoliths Hanus et al, 2015Hanus et al, , 2018Landsman et al, 2018;Rozitis and Green, 2014;Rozitis et al, , 2018.…”