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Register a new userProperties of slowly rotating asteroids from the Convex Inversion Thermophysical Model
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Results from the TESS mission showed that previous studies strngly underestimated the number of slow rotators, revealing the importance of studying those asteroids. For most slowly rotating asteroids (P > 12), no spin and shape model is available because of observation selection effects. This hampers determination of their thermal parameters and accurate sizes. We continue our campaign in minimising selection effects among main belt asteroids. Our targets are slow rotators with low light-curve amplitudes. The goal is to provide their scaled spin and shape models together with thermal inertia, albedo, and surface roughness to complete the statistics. Rich multi-apparition datasets of dense light curves are supplemented with data from Kepler and TESS. In addition to data in the visible range, we also use thermal data from infrared space observatories (IRAS, Akari and WISE) in a combined optimisation process using the Convex Inversion Thermophysical Model (CITPM). This novel method has so far been applied to only a few targets, and in this work we further validate the method. We present the models of 16 slow rotators. All provide good fits to both thermal and visible data. The obtained sizes are on average accurate at the 5% precision, with diameters in the range from 25 to 145 km. The rotation periods of our targets range from 11 to 59 hours, and the thermal inertia covers a wide range of values, from 2 to <400 SI units, not showing any correlation with the period. With this work we increase the sample of slow rotators with reliable spin and shape models and known thermal inertia by 40%. The thermal inertia values of our sample do not display a previously suggested increasing trend with rotation period, which might be due to their small skin depth.
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Context. Earlier work suggests that slowly rotating asteroids should have higher thermal inertias than faster rotators because the heat wave penetrates deeper into the sub-surface. However, thermal inertias have been determined mainly for fast rotators due to selection effects in the available photometry used to obtain shape models required for thermophysical modelling (TPM). Aims. Our aims are to mitigate these selection effects by producing shape models of slow rotators, to scale them and compute their thermal inertia with TPM, and to verify whether thermal inertia increases with the rotation period. Methods. To decrease the bias against slow rotators, we conducted a photometric observing campaign of main-belt asteroids with periods longer than 12 hours, from multiple stations worldwide, adding in some cases data from WISE and Kepler space telescopes. For spin and shape reconstruction we used the lightcurve inversion method, and to derive thermal inertias we applied a thermophysical model to fit available infrared data from IRAS, AKARI, and WISE. Results. We present new models of 11 slow rotators that provide a good fit to the thermal data. In two cases, the TPM analysis showed a clear preference for one of the two possible mirror solutions. We derived the diameters and albedos of our targets in addition to their thermal inertias, which ranged between 3$^{+33}_{-3}$ and 45$^{+60}_{-30}$ Jm$^{-2}$s$^{-1/2}$K$^{-1}$. Conclusions. Together with our previous work, we have analysed 16 slow rotators from our dense survey with sizes between 30 and 150 km. The current sample thermal inertias vary widely, which does not confirm the earlier suggestion that slower rotators have higher thermal inertias.
Themis family is one of the largest and oldest asteroid populations in the main-belt. Water-ice may widely exist on the parent body (24) Themis. In this work, we employ the Advanced Thermophysical Model as well as mid-infrared measurements from NASAs Wide-Field Infrared Survey Explorer to explore thermal parameters of 20 Themis family members. Here we show that the average thermal inertia and geometric albedo are ~$39.5pm26.0 ~rm J m^{-2} s^{-1/2} K^{-1}$ and $0.067pm0.018$, respectively. The family members have a relatively moderate roughness fraction on their surfaces. We find that the relatively low albedos of Themis members are consistent with the typical values of B-type and C-type asteroids. As aforementioned, Themis family bears a very low thermal inertia, which indicates a fine and mature regolith on their surfaces. The resemblance of thermal inertia and geometric albedo of Themis members may reveal their close connection in origin and evolution. In addition, we present the compared results of thermal parameters for several prominent families.
Aims. To derive the thermal inertia of 2008 EV$_5$, the baseline target for the Marco Polo-R mission proposal, and infer information about the size of the particles on its surface. Methods. Values of thermal inertia are obtained by fitting an asteroid thermophysical model to NASAs Wide-field Infrared Survey Explorer (WISE) infrared data. From the constrained thermal inertia and a model of heat conductivity that accounts for different values of the packing fraction (a measure of the degree of compaction of the regolith particles), grain size is derived. Results. We obtain an effective diameter $D = 370 pm 6,mathrm{m}$, geometric visible albedo $p_V = 0.13 pm 0.05$ (assuming $H=20.0 pm 0.4$), and thermal inertia $Gamma = 450 pm 60$ J/m2/s(1/2)/K at the 1-$sigma$ level of significance for its retrograde spin pole solution. The regolith particles radius is $r = 6.6^{+1.3}_{-1.3}$ mm for low degrees of compaction, and $r = 12.5^{+2.7}_{-2.6}$ mm for the highest packing densities.
Context. Cometary dust particles are subjected to various forces after being lifted off the nucleus. These forces define the dynamics of dust, trajectories, alignment, and fragmentation, which, in turn, have a significant effect on the particle distribution in the coma. Aims. We develop a numerical thermophysical model that is applicable to icy cometary dust to study the forces attributed to the sublimation of ice. Methods. We extended the recently introduced synoptic model for ice-free dust particles to ice-containing dust. We introduced an additional source term to the energy balance equation accounting for the heat of sublimation and condensation. We use the direct simulation Monte Carlo approach with the dusty gas model to solve the mass balance equation and the energy balance equation simultaneously. Results. The numerical tests show that the proposed method can be applied for dust particles covering the size range from tens of microns to centimeters with a moderate computational cost. We predict that for an assumed ice volume fraction of 0.05, particles with a radius, r >> 1 mm, at 1.35 AU, may disintegrate into mm-sized fragments due to internal pressure build-up. Particles with r < 1 cm lose their ice content within minutes. Hence, we expect that only particles with r > 1cm may demonstrate sustained sublimation and the resulting outgassing forces.
Jupiter has nearly 8000~known co-orbital asteroids orbiting in the L4 and L5 Lagrange points called Jupiter Trojan asteroids. Aside from the greater number density of the L4 cloud the two clouds are in many ways considered to be identical. Using sparse photometric data taken by the Asteroid Terrestrial-impact Last Alert System (ATLAS) for 863 L4 Trojans and 380 L5 Trojans we derive the shape distribution for each of the clouds and find that, on average, the L4 asteroids are more elongated than the L5 asteroids. This shape difference is most likely due to the greater collision rate in the L4 cloud that results from its larger population. We additionally present the phase functions and $c-o$ colours of 266~objects.
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