Estimates of rotation periods for Jupiter Trojans with the Zwicky Transient Facility photometric lightcurves

We present new rotational period estimates for 216 Jupiter Trojans using photometric data from the Zwicky Transient Facility (ZTF), including 80 Trojans with previously unknown periods. Our analysis reveals rotation periods ranging from 4.6 h to 447.8 h. These results support the existence of a spin barrier for Trojans larger than 10 km, with periods clustering between 4 and 4.8 h. This spin barrier is roughly twice as long as that observed for main-belt asteroids, suggesting that Jupiter Trojans have significantly lower bulk densities, likely due to a higher fraction of ices and volatile materials in their composition. We identify three new Trojans with reliable rotation periods near the spin barrier, doubling the number of known Trojans in this critical period range. Using these results, we estimate a mean density of $\sim 0.52{\mathrm{g/cm}}^3$ for rubble-pile Trojans. Our findings contribute to the growing body of evidence that many Trojans are rubble-pile bodies with distinct physical properties compared to main-belt asteroids. Looking forward, we anticipate that forthcoming data from the Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST) will provide rotational period estimates for several hundred thousand Trojans, down to objects as small as 1 km, enabling a more detailed investigation of their rotational properties and internal structure.