An ALMA search for high albedo objects among the mid-sized Jupiter Trojan population

TL;DR

This study uses ALMA thermal emission data combined with optical measurements to identify high albedo objects among mid-sized Jupiter Trojans, suggesting some may contain high-albedo materials like ices.

Contribution

It introduces a method combining ALMA and Zwicky Transient Facility data to accurately measure albedos and identify high albedo Jupiter Trojans, revealing potential icy interiors.

Findings

Several small Trojans have high albedos confirmed by ALMA and WISE.

The number of high albedo objects aligns with impact-based formation theories.

Some Trojans may contain high-albedo materials such as ices.

Abstract

We use ALMA measurements of 870 $\mu$m thermal emission from a sample of mid-sized (15-40 km diameter) Jupiter Trojan asteroids to search for high albedo objects in this population. We calculate the diameters and albedos of each object using a thermal model which also incorporates {contemporaneous} Zwicky Transient Facility photometry to accurately measure the absolute magnitude at the time of the ALMA observation. We find that while many albedos are lower than reported from WISE, several small Trojans have high albedos independently measured both from ALMA and from WISE. The number of these high albedo objects is approximately consistent with expectations of the number of objects that recently have undergone large-scale impacts, suggesting that the interiors of freshly-crated Jupiter Trojans could contain high albedo materials such as ices.