Masses, bulk densities, and macroporosities of asteroids (15) Eunomia, (29) Amphitrite, (52) Europa, and (445) Edna based on Gaia astrometry

TL;DR

This study utilizes Gaia DR2 astrometry combined with Earth-based data to estimate asteroid masses, densities, and porosities, demonstrating improved accuracy in mass determination for large asteroids through advanced modeling techniques.

Contribution

The paper introduces a Markov chain Monte Carlo method for asteroid mass estimation using Gaia astrometry and validates its effectiveness on multiple asteroids.

Findings

Gaia astrometry significantly improves mass estimates when combined with Earth data.

Mass estimation for (445) Edna requires multiple data sources for accuracy.

Orbit solutions are refined, notably for asteroid (367) Amicitia.

Abstract

Gaia Data Release 2 (DR2) includes milliarcsecond-accuracy astrometry for 14,099 asteroids. We explore the practical impact of this data for the purpose of asteroid mass and orbit estimation by estimating the masses individually for four large asteroids. We use various combinations of Gaia astrometry and/or Earth-based astrometry so as to determine the impact of Gaia on the estimated masses. By utilizing published information about estimated volumes and meteorite analogs, we also derive estimates for bulk densities and macroporosities. We apply a Markov chain Monte Carlo (MCMC) algorithm for asteroid mass and orbit estimation by modeling asteroid-asteroid close encounters to four separate large asteroids in an attempt to estimate their masses based on multiple simultaneously studied close encounters with multiple test asteroids. In order to validate our algorithm and data treatment, we apply the MCMC algorithm to pure orbit determination for the main-belt asteroid (367) Amicitia and compare the residuals to previously published ones. In addition, we attempt to estimate a mass for (445) Edna with Gaia astrometry alone based on its close encounter with (1764) Cogshall. In the case of the orbit of (367) Amicitia, we find a solution that improves on the previously published solution. The study of (445) Edna reveals that mass estimation with DR2 astrometry alone is unfeasible and that it must be combined with astrometry from other sources to achieve meaningful results. We find that a combination of DR2 and Earth-based astrometry results in dramatically reduced uncertainties and, by extension, significantly improved results in comparison to those computed based on less accurate Earth-based astrometry alone.