Component properties and mutual orbit of binary main-belt comet 288P/(300163) 2006 VW139
Agarwal, J.; Weaver, H.; Larson, S.; Kim, Y.; Mutchler, M.; Jewitt, D.
Germany, United States
Abstract
Context. The binary asteroid 288P/(300163) is unusual both for its combination of wide-separation and high mass ratio and for its comet-like activity. It is not currently known whether there is a causal connection between the activity and the unusual orbit or if instead the activity helped to overcome a strong detection bias against such sub-arcsecond systems.
Aims: We aim to find observational constraints discriminating between possible formation scenarios and to characterise the physical properties of the system components.
Methods: We measured the component separation and brightness using point spread function fitting to high-resolution Hubble Space Telescope/Wide Field Camera 3 images from 25 epochs between 2011 and 2020. We constrained component sizes and shapes from the photometry, and we fitted a Keplerian orbit to the separation as a function of time.
Results: Approximating the components A and B as prolate spheroids with semi-axis lengths a < b and assuming a geometric albedo of 0.07, we find aA ≤ 0.6 km, bA ≥ 1.4 km, aB ≤ 0.5 km, and bB ≥ 0.8 km. We find indications that the dust production may have concentrated around B and that the mutual orbital period may have changed by 1-2 days during the 2016 perihelion passage. Orbit solutions have semi-major axes in the range of (105-109) km, eccentricities between 0.41 and 0.51, and periods of (117.3-117.5) days pre-perihelion and (118.5-119.5) days post-perihelion, corresponding to system masses in the range of (6.67-7.23) × 1012 kg. The mutual and heliocentric orbit planes are roughly aligned.
Conclusions: Based on the orbit alignment, we infer that spin-up of the precursor by the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect led to the formation of the binary system. We disfavour (but cannot exclude) a scenario of very recent formation where activity was directly triggered by the break-up, because our data support a scenario with a single active component.