An astrometric mass estimate for asteroid (223) Rosa

Outer main belt asteroid (223) Rosa is a possible flyby target of opportunity for ESA’s (European Space Agency) JUpiter ICy moons Explorer (JUICE) mission when passing the asteroid belt on the way to Jupiter. The very low albedo and the featureless red spectra indicate a P-type asteroid in the Tholen taxonomy, though the yet known bulk density 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. The mass of Rosa was derived by analyzing the gravitational deflection of small `test’ asteroids which had a close encounter with Rosa in the past. To find such events suitable for the mass determination, an encounter search with about 900,000 asteroids over the time span $1980-2030$ was performed. Three encounters were identified from which two independent mass estimates for Rosa were derived: $M=(5.32\pm 2.17)\times {10}^{17}$ kg and $M=(3.15\pm 1.14)\times {10}^{17}$ kg, respectively. The weighted mean is $M=(3.62\pm 1.25)\times {10}^{17}$ kg. This yields to a bulk density of $\rho =1.2\pm 0.5\mathrm{g}\mathrm{c}{\mathrm{m}}^{-3}$, when adopting an effective diameter of $D=83\pm 8$ km. This bulk density estimate is consistent with typical densities for Tholen taxonomy P-type asteroids.