Orbital stability analysis and photometric characterization of the second Earth Trojan asteroid 2020 XL(5)

Trojan asteroids are small bodies orbiting around the L(4) or L(5) Lagrangian points of a Sun-planet system. Due to their peculiar orbits, they provide key constraints to the Solar System evolution models. Despite numerous dedicated observational efforts in the last decade, asteroid 2010 TK(7) has been the only known Earth Trojan thus far. Here we confirm that the recently discovered 2020 XL(5) is the second transient Earth Trojan known. To study its orbit, we used archival data from 2012 to 2019 and observed the object in 2021 from three ground-based observatories. Our study of its orbital stability shows that 2020 XL(5) will remain in L(4) for at least 4 000 years. With a photometric analysis we estimate its absolute magnitude to be [Formula: see text] , and color indices suggestive of a C-complex taxonomy. Assuming an albedo of 0.06 ± 0.03, we obtain a diameter of 1.18 ± 0.08 km, larger than the first known Earth Trojan asteroid.