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Determination of mass and bulk density of asteroid (21) Lutetia using Rosetta radio tracking data

Mass and bulk density of asteroids, which could be determined to high precision through spacecraft flyby, are critical to understanding their interior structures and compositions. In this paper, the Rosetta spacecraft radio tracking data were used to determine the mass of the asteroid based on self-developed software tools. Using the volume model of Lutetia determined by Rosetta science camera, the bulk density was estimated. For extracting contributions only associated with Lutetia, an effective model was established and the detailed mathematical formula was developed to remove the additional frequency shift induced by HGA slew motion accounting for two degrees of freedom in azimuth and elevation angle. In addition, two available solution scenarios were applied in order to obtain reliable solution and the detailed discussion about parameter correlation and solution stability were performed based on properties of parameters and fly-by geometry. All of above yielded a mass of (1.696 ±0.014)×1018 kg (1 σ , error 0.85%) and the bulk density(3.4 ±0.3)×103 kg/m3 at last. The values were almost the same as which was achieved by Rosetta Science Team and the precision of the asteroid mass was improved by 15%.