Speaker
Description
The orbital changes during a close encounter between a perturber asteroid and a test asteroid can be analyzed to estimate the mass of the perturber. The changes are constrained with astrometric observations, making precise astrometry vital for asteroid-mass estimation. Currently, the best astrometry for the purpose of mass estimation comes from ESA’s Gaia mission, which provides astrometry of asteroids at an unprecedented accuracy measured, at best, in sub-milliarcseconds. Gaia’s third data release (DR3) [1] did not yet contain enough data to alone constrain asteroid masses, but Focused Product Release (FPR) [2] and the upcoming DR4 nearly doubles the available data and could be enough. Combining FPR data with ground-based astrometry has already been investigated and it increased the number of asteroids with meaningful mass estimates [4]. In turn, we investigate the extent to which only FPR can be utilized in mass estimation, without the addition of ground-based astrometry.
However, in order to best utilize Gaia astrometry, we have to consider Gaia’s decrease in accuracy for larger asteroids, typical mass-estimation targets, due to shape and size effects, such as the photocenter-barycenter offset. The misalignment of the apparent photocenter and true barycenter becomes an issue when attempting to derive an orbit for a target, or making any subsequent deductions based on orbits, because the orbit tracks the barycenter. Previous studies [1],[3] show that correcting for the offset improves orbital fitting in terms of residuals in Gaia’s along-scan direction.
Here, our focus is discussing mass estimation for DR3 and FPR data with Markov chain Monte Carlo methods (see, e.g., [7]) as well as a new mass estimation method, the mass marching inverse method, which is implemented as part of the open-source orbital-computation software, OpenOrb [5]. We also present results of work we have done on photocenter-barycenter offset correction (for the method see, e.g., [6]), which are in line with previous studies: residuals in Gaia’s along-scan direction improve and the number of outliers rejected from orbital fitting is reduced.
[1] Gaia collaboration, P. Tanga et al. 2023, Astronomy and astrophysics, 674, A12
[2] Gaia collaboration, P. David et al. 2023, Astronomy and astrophysics, 680, A37
[3] O. Fuentes-Muñoz et al. 2024, The Astronomical journal, 167, 290
[4] O. Fuentes-Muñoz et al. 2025, The Astronomical journal, 170, 353
[5] M. Granvik et al. 2009, Meteoritics and Planetary Science, 44, 1853
[6] K. Muinonen and K. Lumme 2015, Astronomy and astrophysics, 584, A23
[7] L. Siltala and M. Granvik 2020, Astronomy and astrophysics, 633, A46