(121514) 1999 UJ7: A primitive, slow-rotating Martian Trojan★
Armagh Observatory and Planetarium, College Hill,
Armagh BT61 9DG,
Northern Ireland, UK
2 Institute of Astronomy and NAO, Bulgarian Academy of Sciences, 72, Tsarigradsko Chaussée Blvd., 1784 Sofia, Bulgaria
3 IMCCE, Observatoire de Paris, UPMC, CNRS UMR8028, 77 Av. Denfert-Rochereau, 75014 Paris, France
4 INAF – Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese (TO), Italy
5 INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125, Firenze, Italy
Accepted: 7 August 2018
Aims. The goal of this investigation is to determine the origin and surface composition of the asteroid (121514) 1999 UJ7, the only currently known L4 Martian Trojan asteroid.
Methods. We have obtained visible reflectance spectra and photometry of 1999 UJ7 and compared the spectroscopic results with the spectra of a number of taxonomic classes and subclasses. A light curve was obtained and analysed to determine the asteroid spin state.
Results. The visible spectrum of 1999 UJ7 exhibits a negative slope in the blue region and the presence of a wide and deep absorption feature centred around ~0.65 μm. The overall morphology of the spectrum seems to suggest a C-complex taxonomy. The photometric behaviour is fairly complex. The light curve shows a primary period of 1.936 d, but this is derived using only a subset of the photometric data. The asteroid may be in a non-principal axis rotational state, but our observational coverage is insufficient to draw definitive conclusions.
Conclusions. Although the observed spectral absorption is wider and deeper, this finding may be compatible with the 0.7 μm spectral feature exhibited by some Ch-type asteroids and could possibly be interpreted as diagnostic of the presence of hydrated minerals. The inferred composition of 1999 UJ7 as a primitive object can be consistent with a volatile-rich object originally accreted beyond the snow line of the solar system, and subsequently evolved to reach the inner regions of the solar system.
Key words: planets and satellites: individual: Mars / planets and satellites: individual: Trojan asteroids / techniques: imaging spectroscopy / techniques: photometric
Based on service observations made with the 4.2 m William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group of Telescopes in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias and on data collected with 2 m Ritchey-Chrétien-Coudé (2mRCC) Telescope at Rozhen National Astronomical Observatory.
© ESO 2018