Ultraviolet to near-infrared spectroscopy of the potentially hazardous, low delta-V asteroid (175706) 1996 FG3

Backup target of the sample return mission MarcoPolo-R^⋆

¹ LESIA – Observatoire de Paris, CNRS, UPMC Univ. Paris 06, Univ. Paris-Diderot, 5 place J. Janssen, 92195 Meudon, France
e-mail: davide.perna@obspm.fr
² INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monte Porzio Catone, Roma, Italy
³ Univ. Paris Diderot, Sorbonne Paris Cité, 4 rue Elsa Morante, 75205 Paris, France
⁴ Observatório Nacional, COAA, Rua Gal. José Cristino 77, 20921-400 Rio de Janeiro, Brazil
⁵ Instituto de Astrofísica de Andalucía – CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
⁶ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago 19, Chile
⁷ INAF – Osservatorio Astrofisico di Arcetri, L.go E. Fermi 5, 50125 Firenze, Italy
⁸ IFAC – CNR, Via Madonna del Piano 10, 50019 Sesto Fiorentino ( FI), Italy

Received: 10 April 2013
Accepted: 16 May 2013

Abstract

Context. Primitive near-Earth asteroids (NEAs) are important subjects of study for current planetary research. Their investigation can provide crucial information on topics such as the formation of the solar system, the emergence of life, and the mitigation of the risk of asteroid impact. Sample return missions from primitive asteroids have been scheduled or are being studied by space agencies, including the MarcoPolo-R mission selected for the assessment study phase of ESA M3 missions.

Aims. We want to improve our knowledge of the surface composition and physical nature of the potentially hazardous, low delta-V asteroid (175706) 1996 FG3, backup target of MarcoPolo-R. This intriguing object shows an as-yet unexplained spectral variability.

Methods. We performed spectroscopic observations of 1996 FG3 using the visible spectrograph DOLORES at the Telescopio Nazionale Galileo (TNG), and the UV-to-NIR X-Shooter instrument at the ESO Very Large Telescope (VLT).

Results. We find featureless spectra and we classify 1996 FG3 as a primitive Xc-type in the Bus-DeMeo taxonomy. Based on literature comparison, we confirm the spectral variability of this object at near-infrared (NIR) wavelengths, and find that spectral variations exist also for the visible spectral region. Phase reddening cannot explain such variations. Obtained with the same observational conditions for the whole 0.3–2.2 μm range, our X-Shooter spectrum allowed a proper comparison with the RELAB meteorite database. A very good fit is obtained with the very primitive C2 Tagish Lake carbonaceous chondrite (pressed powder), confirming 1996 FG3 as a suitable target for a sample return mission from primitive NEAs.

Conclusions. We hypothesize a compacted/cemented surface for 1996 FG3, like that observed by the Hayabusa mission on (25143) Itokawa, with the possible presence of regions showing different degrees of surface roughness. This variegation could be related to the binary nature of 1996 FG3, but to check this hypothesis further observations are necessary.