Physical, spectral, and dynamical properties of asteroid (107) Camilla and its satellites

Abstract

The population of large 100+ km asteroids is thought to be primordial. As such, they are the most direct witnesses of the early history of our Solar System available. Those among them with satellites allow study of the mass, and hence density and internal structure. We study here the dynamical, physical, and spectral properties of the triple asteroid (107) Camilla from lightcurves, stellar occultations, optical spectroscopy, and high-contrast and high-angular-resolution images and spectro-images.Using 80 positions measured over 15 years, we determine the orbit of its larger satellite, S/2001 (107) 1, to be circular, equatorial, and prograde, with root-mean-square residuals of 7.8 mas, corresponding to a sub-pixel accuracy. From 11 positions spread over three epochs only, in 2015 and 2016, we determine a preliminary orbit for the second satellite S/2016 (107) 1. We find the orbit to be somewhat eccentric and slightly inclined to the primary's equatorial plane, reminiscent of the properties of inner satellites of other asteroid triple systems. Comparison of the near-infrared spectrum of the larger satellite reveals no significant difference with Camilla. Hence, both dynamical and surface properties argue for a formation of the satellites by excavation from impact and re-accumulation of ejecta in orbit.We determine the spin and 3-D shape of Camilla. The model fits well each data set: lightcurves, adaptive-optics images, and stellar occultations. We determine Camilla to be larger than reported from modeling of mid-infrared photometry, with a sphericalvolume-equivalent diameter of 254 ± 36 km (3 σ uncertainty), in agreement with recent results from shape modeling (Hanus et al., 2017, A&A 601). Combining the mass of (1.12 ± 0.01) × 10 19 kg (3 σ uncertainty) determined from the dynamics of the satellites and the volume from the 3-D shape model, we determine a density of 1,280 ± 130 kg·m −3 (3 σ uncertainty). From this density, and considering Camilla's spectral similarities with (24) Themis and (65) Cybele (for which water ice coating on surface grains was reported), we infer a silicate-to-ice mass ratio of 1-6, with a 10-30% macroporosity.

Homogeneous internal structure of CM-like asteroid (41) Daphne

“…The results of this approach have already been demonstrated elsewhere (e.g., Witasse et al, 2006;Drummond et al, 2014). In parallel, the diffused halo of light surrounding Daphne was removed by subtracting concentric annuli (as described thoroughly in Pajuelo et al, 2018) for satellite detection.…”

“…This was achieved by measuring the background at the location of the moon for each pixel as the median value of the area defined as a 40 ×1-pixel arc centered on Daphne. To estimate the uncertainty and potential bias on photometry (at each wavelength) introduced by this method, we performed a number of simulations (similarly to our study of the satellite of Camilla, see Pajuelo et al, 2018). We added synthetic companions on the 39 spectral images of the spectro-imaging cube, at a similar separation to the satellite (≈300 mas) and random position angles from the primary.…”

“…The high-quality correction delivered by the AO system of SPHERE (Fusco et al, 2006(Fusco et al, , 2014 compared to previous generations of AO cameras, and the use of shorter wavelength (visible R band compared to the near-infrared J/H/K bands typically used with previous cameras), provides a twofold to threefold improvement in angular resolution. This sharper resolution allows the detailed modeling of asteroid shapes and enhanced satellite detection capability, as recently illustrated on the main-belt asteroids (3) Juno, (6) Hebe, (16) Psyche, (89) Julia, (107) Camilla, and (130) Elektra (Viikinkoski et al, 2015(Viikinkoski et al, , 2018Marsset et al, 2016Marsset et al, , 2017aYang et al, 2016;Hanuš et al, 2017a;Pajuelo et al, 2018;Vernazza et al, 2018).…”

IDP-like Asteroids Formed Later than 5 Myr After Ca–Al-rich Inclusions

“…Instead, their surfaces comprise likely indigenous anhydrous silicates (e.g., Emery et al 2006;Vernazza et al 2012Vernazza et al , 2015 and water ice (Campins et al 2010;Rivkin & Emery 2010;Licandro et al 2011;Hargrove et al 2012;Takir & Emery 2012). The higher bulk abundances of low-density volatiles (ices) in these bodies is also indicated by lower observed bulk densities, near 1500 kg m −3 but possibly as low as 800 kg m −3 Pajuelo et al 2018;Castillo-Rogez et al 2019, and references therein). Those of the Jupiter Trojans Hektor and Patroclus are also in this range (Marchis et al 2014;Emery et al 2015 and references therein).…”

Volume uncertainty assessment method of asteroid models from disc-integrated visual photometry

“…The latter results in model that explains different datasets simultaneously rather than being simply scaled, which is a great advantage of multi-dataset inversion. Although limited to a small number of targets, it provides valuable and detailed information about them (Carry et al 2008;Berthier et al 2014;Pajuelo et al 2018;Vernazza et al 2018).…”