An astrometric mass estimate for asteroid (223) Rosa

Outer main belt asteroid (223) Rosa has been proposed as potential ESA JUICE mission flyby target of opportunity on its way to Jupiter (Avdellidou et al. 2021, Agostini et al. 2022). Rosa is a very dark (p < 0.05) object, with an effective diameter D of about 83 km. The very low albedo and the featureless red spectra indicate a P-type asteroid in the Tholen taxonomy, though the yet known bulk density estimates (2.0 ± 1.1 g cm⁻³ and 3.1 g cm⁻³; derived from masses by Fienga et al. 2019 and Park et al. 2021; see also Avdellidou et al. 2021) did not match very well this classification.

Aim of this work was to derive new estimates for the mass and for the bulk density for (223) Rosa. From the gravitational deflection on two small 'test' asteroids during close encounters with the perturber, namely (35525) 1998 FV64 on 2010-12-31.87 and (315162) 2007 FL24 on 2016-07-04.05, the mass of Rosa was derived as M = (3.62 ± 1.25) × 10¹⁷ kg (weighted mean of both results). This yields to a bulk density ρ = 1.2 ± 0.5 g cm⁻³, when adopting an effective diameter of D = 83 ± 8 km, as average of the available literature values. This density agrees well with typical densities for P-type asteroids like (87) Sylvia and (107) Camilla (ρ ≈ 1.3 g cm⁻³ ; see e.g. Carry et al. (2021), Vernazza et al. (2021)).

References
Agostini, L., Lucchetti, A., Pajola, M., et al. 2022, Planetary and Space Science, 216, 105476
Avdellidou, C., Pajola, M., Lucchetti, A., et al. 2021, A&A, 656, L18
Fienga, A., Deram, P., Viswanathan, V., et al. 2019, Notes Scientifiques et Techniques de l’Institut de Mecanique Celeste, 109
Carry, B., Vernazza, P., Vachier, F., et al. 2021, A&A, 650, A129
Park, R. S., Folkner, W. M., Williams, J. G., & Boggs, D. H. 2021, AJ, 161, 105
Vernazza, P., Ferrais, M., Jorda, L., et al. 2021, A&A, 654, A56