Visible region spectral similarity of low-albedo Mars Trojan 1999 UJ7 to T-type asteroids and to the martian moons

Visible-band spectrophotometry of (121514) 1999 UJ 7 , a low-albedo dynamically stable resident at the L 4 Lagrangian point of Mars, was carried out with the OSIRIS imager/spectrograph on the 10.4 m Gran Telescopio Canarias. We classify the linear, generally featureless spectrum as T-type or D-type in the Bus taxonomy or M-/P-class in the recent (Mahlke et al., 2022) taxonomy. We also report the detection of a shallow ( ∼ 1%) absorption feature centred at 0.63- 0 . 64 μ m , possibly related to water-of-hydration 0.7- μ m absorption found in spectra of other low-albedo asteroids. The moderately high slope ( ∼ 0.6 μ m − 1 ) and position of the shallow absorption match features found in visible spectra of T-type main-belt asteroids as well as spectra of the martian moons. Analysis of the new spectrum strengthens the case that this Mars Trojan is a volatile-rich early migrant from the outer solar system.