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تسجيل مستخدم جديدRevisiting Advanced Thermal Physical Model: New Perspectives on Thermophysical Characteristics of (341843) 2008 EV5 from Four-bands WISE Data with Sunlight-Reflection Model
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In this paper, we investigate thermophysical characteristics of near-Earth asteroid (341843) 2008 EV5, based on our improved Advanced Thermal Physical Model (ATPM) by considering the contribution of sunlight-reflection for rough surface, along with four wavebands observations from Wide-field Infrared Survey Explorer (WISE) and the radar-derived shape model. Here we derive that 2008 EV5 has a relatively low thermal inertia of $Gamma=110 _{-12}^{+40}rm~J m^{-2} s^{-1/2} K^{-1}$ but a high roughness fraction. The geometric albedo and effective diameter are then constrained to be $p_v=0.095_{-0.003}^{+0.016}$ and $D_{rm eff}=431_{-33}^{+6}rm~m$, respectively. The low thermal inertia indicates that 2008 EV5 may have undergone sufficient space weathering over secular evolution. The high roughness may have resemblances to the appearances of Bennu and Ryugu recently observed by spacecrafts, where a great number of boulders are widely distributed on the asteroids surface. Moreover, we numerically perform 1000 backward simulations of 2008 EV5s cloned orbits within 1 Myr to explore its origin, and present a probability of $sim6.1%$ that the asteroid originates from the main belt. Finally, we estimate that the mean grain size of the surface ranges from 0.58 to 1.3 mm, and infer that it is unlikely to find water ice on most area of 2008 EV5, but there may exist water ice on high-latitudes near polar region.
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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 asteroi
d 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.
With the Wide-field Infrared Survey Explorer (WISE; Wright et al. 2010), we have observed over 157,000 minor planets (Mainzer et al. 2011). Included in these are a number of near-Earth objects, Main Belt Asteroids, and irregular satellites which have
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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 bec
ause 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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The Asteroid Redirect Mission (ARM) under development by NASA is being planned to collect a multi-meter boulder from a near-Earth asteroid (NEA), and to bring it to the cis-lunar space in the mid-2020s for future study and exploitation by a crewed mi
ssion. The MarcoPolo-M5 project is being proposed in 2016 for the M5 mission opportunity by ESA, to bring back to Earth a sample from a very primitive D-type NEA. We aim to further characterize the physical properties of two optimal targets for sample return space missions, the low-DeltaV NEAs (341843) 2008 EV5 and (52381) 1993 HA. 2008 EV5 is the baseline target of ARM, but only one spectrum of this object exists in the literature. 1993 HA is a very favourable target for a space mission based on its dynamical properties: here we intend to assess if it is a suitable target for MarcoPolo-M5. We obtained visible spectroscopy of 2008 EV5 with the FORS2 instrument at ESO-VLT, at different rotational phases. We also obtained visible and near-infrared spectroscopy of 1993 HA, using the EFOSC2 and SOfI instruments at ESO-NTT. Visible photometry of 1993 HA was carried out within the IMPACTON project at the Observatorio Astronomico do Sertao de Itaparica (Brazil). Our new observations are in agreement with the C-type classification of 2008 EV5. We obtained five visible spectra which do not show any variability within the limits of noise, suggesting a homogeneous surface. We obtained the first ever spectroscopic dataset for 1993 HA, finding a featureless, red-sloped behaviour typical of D-types. We found that the synodic rotation period of 1993 HA is 4.107+-0.002 h. The derived lightcurve also suggests an elongated shape (axis ratio a/b>=1.71). At this stage 1993 HA does indeed seem to be the most favourable target for MarcoPolo-M5, though future observations are necessary to study it further.
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