Dynamics of 2023 FW14, the second L4 Mars trojan, and a physical characterization using the 10.4 m Gran Telescopio Canarias

Known Mars trojans could be primordial small bodies that have remained in their present-day orbits for the age of the Solar System. Their orbital distribution is strongly asymmetric; there are over a dozen objects at the L$_ $ point and just one at L$_ $, (121514) 1999 UJ$_ $. Most L$_ $ trojans appear to form a collision-induced asteroid cluster, known as the Eureka family. Asteroid 2023 FW$_ $ was recently discovered and it has a robust orbit determination that may be consistent with a Mars trojan status. Our aim is determine the nature and dynamical properties of 2023 FW$_ We carried out an observational study of 2023 FW$_ $ to derive its spectral class using the OSIRIS camera spectrograph at the 10.4 m Gran Telescopio Canarias. We investigated its possible trojan resonance with Mars using direct $N$-body simulations. The reflectance spectrum of 2023 FW$_ $ is not compatible with the olivine-rich composition of the Eureka family; it also does not resemble the composition of the Moon, although (101429) 1998 VF$_ $ does. The Eureka family and 101429 are at the L$_ $ point. The spectrum of 2023 FW$_ $ is also different from two out of the three spectra in the literature of the other known L$_ $ trojan, 121514, which are of C-type. The visible spectrum of 2023 FW$_ $ is consistent with that of an X-type asteroid, as is the third spectrum of 121514. Our calculations confirm that 2023 FW$_ $ is the second known L$_ $ Mars trojan although it is unlikely to be primordial; it may remain in its present-day ``tadpole'' path for several million years before transferring to a Mars-crossing orbit. It might be a fragment of 121514, but a capture scenario seems more likely. The discovery of 2023 FW$_ $ suggests that regular Mars-crossing asteroids can be captured as temporary Mars trojans.