Asteroid Mass Estimation with the Third Gaia Data Release

The classical approach to estimate an asteroid's mass is to analyze its gravitational interactions with another object such as a spacecraft, Mars, a companion asteroid, or a separate asteroid during an asteroid-asteroid close encounter. The latter case leads to gravitational perturbations on a small, generally assumed massless, test asteroid, by the larger perturber asteroid involved in the encounter. By measuring and modeling these perturbations it is possible to estimate the mass of the larger asteroid. This can be described as an inverse problem where the aim is to fit six orbital elements for each asteroid in addition to masses for the perturbing asteroids into astrometric data for each asteroid.

Given that the signals of the perturbations are generally very weak, high precision astrometry and long observational arcs are vital for estimating asteroid masses with acceptable accuracy. It follows that the milliarcsecond-precision astrometry produced by the Gaia spacecraft is a great boon to the field and asteroid mass estimation is considered one of the main applications of Gaia's Solar System Object (SSO) astrometry (Gaia Collaboration et al. 2018a). Indeed, we have recently demonstrated that usage of SSO astrometry from the second Gaia Data Release (DR2) (Gaia Collaboration et al. 2018b) in combination with Earth-based astrometry can reduce the associated uncertainties by up to an order of magnitude in comparison to results computed with Earth-based alone (Siltala & Granvik 2022). In that work, we observed that DR2 does remain limited by the relatively short observational arc of the astrometry as well as the low number (14,099) of asteroids included, which excludes a large number of potentially interesting asteroids.

The third Gaia Data Release (DR3), to be released in June 2022, is expected to remedy these issues to a certain extent. DR3 will include astrometry approximately 11 times more asteroids (158,152) over a much longer timespan. In addition, the SSO data processing has improved and correspondingly we expect further improvements in data quality. Thus, DR3 will enable a large number of asteroid mass estimates beyond what is already possible with DR2 while leading to further improvements to the uncertainties of the masses in cases where DR2 was already usable.

In this presentation, we demonstrate the practical impact of DR3 on asteroid mass estimation. We re-compute asteroid masses from several test cases we previously studied with Gaia DR2 and compare the results to those previously obtained in Siltala & Granvik 2022. Both mass estimation with DR3 alone and in combination with Earth-based astrometry are attempted. Such comparisons will reveal the extent of the improvements to asteroid masses enabled by DR3.

Finally, we briefly discuss future prospects for the application of DR3 to mass estimation, including a comprehensive study of a much larger sample of asteroids,

References
Gaia Collaboration, Spoto, F., Tanga, P., Mignard, F., and 621 co-authors (2018a). Gaia Data Release 2. Observations of solar system objects. A&A, 616:A13.

Gaia Collaboration, Brown, A. G. A., Vallenari, A., Prusti, T., and 621 co-authors (2018b). Gaia Data Release 2. Summary of the contents and survey properties. A&A, 616:A1.

Siltala, L. and Granvik, M. (2022). Masses, bulk densities, and macroporosities of asteroids (15) Eunomia, (29) Amphitrite, (52) Europa, and (445) Edna based on Gaia astrometry. A&A, 658:A65.