Searching for Surface Heterogeneity in Asteroids Using Rubin LSST Multi-band Photometry Submitted to the MPC

The Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST) will provide multi-band photometry for a large number of Solar System small bodies. Observations obtained by Rubin Observatory and submitted to the Minor Planet Center under the observatory code X05 are also compiled by the Asteroid Institute, providing convenient access to reported Rubin asteroid photometry.

We use Rubin X05 photometry to search for asteroids showing possible surface heterogeneity. While the standard Wide-Fast-Deep survey cadence is generally sparse for detailed rotational analyses, some observing sequences contain repeated measurements over relatively short time intervals. We focus on such well-sampled cases, selecting asteroids with several hundred or more observations, and construct phased lightcurves separately for each filter.

For a homogeneous asteroid in principal-axis rotation, lightcurves obtained in different filters should show nearly the same rotational morphology, apart from color-dependent magnitude offsets. In contrast, repeatable differences in amplitude, shape, or phase among filters may indicate rotational color variation, albedo variation, or surface heterogeneity. Objects with known or suspected binary or non-principal-axis rotation are excluded from the analysis, and observations obtained under substantially different viewing or phase angle conditions are removed. Multi-filter measurements are then compared at their corresponding rotational phases.

This study explores the potential of Rubin LSST multi-band photometry for identifying surface variations on asteroids. As the number of X05 observations increases, this approach will help identify candidate asteroids with color variations across rotational phase and possible heterogeneous surfaces, providing useful targets for follow-up spectroscopy and dense lightcurve observations.