Characterization of (357439) 2004 BL86 on its close approach to Earth in 2015

¹ Institut de Mécanique Céleste et de Calcul des Éphémérides (IMCCE), Observatoire de Paris, CNRS UMR8028, 77 avenue Denfert-Rochereau, 75014 Paris Cedex, France
e-mail: Mirel.Birlan@imcce.fr
² Romanian Academy, Astronomical Institute, 5 Cuţitul de Argint, 75212 Bucharest, Romania
³ Romanian Academy, Astronomical Institute, Astronomical Observatory Cluj, 19 Cireşilor, 400487 Cluj-Napoca, Romania
⁴ Institute for Space Science, 409-Atomiştilor, 077125 Magurele, Ilfov, Romania
⁵ Isaac Newton Group of Telescopes, Apartado de Correos 321, 38700 Santa Cruz de la Palma, Canary Islands, Spain
⁶ Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK

Received: 4 May 2015
Accepted: 2 July 2015

Abstract

Context. The potentially hazardous asteroid (PHA) (357439) 2004 BL86 grazed Earth on January 26, 2015 at a distance of about 1.2 million km. This favorable geometry allowed observing it to derive its physical and dynamical parameters. (357439) 2004 BL86 was previously estimated to be a 500-m body. We study it also considering possible mechanisms that might mitigate the effect of asteroids that might become dangerous for Earth.

Aims. Physical and dynamical investigations of this peculiar object were performed to be able to characterize this object.

Methods. We used spectral observations obtained in the visible (V) using the Isaac Newton Telescope and in the near-infrared (NIR) using the InfraRed Telescope Facility. A complementary photometric survey during two nights was also provided by the Astronomical Observatory Cluj-Feleacu station in Romania. We anlyzed the data using reliable mathematical tools that were previously published under the acronym M4AST.

Results. VNIR spectral observations classify (357439) 2004 BL86 as V-type asteroid. The mineralogical analysis reveals its similarities to howardite-eucrite-diogenite meteorites. The band analysis reveals that the object is more similar to a eucritic and howarditic composition, and that it originated from the crust of a large parent body. The analysis yields a mineralogical solution of Wo₁₇Fs₃₉ with an error bar of 4%. Based on the average value of the thermal albedo for V-type objects, its diameter was re-estimated to a value of 290 ± 30 m. The dynamical analysis shows a chaotical behavior of (357439) 2004 BL86. The statistics on meteorite falls show that (357439) 2004 BL86 does not appear to significantly contribute to the current howardite-eucrite-diogenite meteorite flux. For the two photometrical observing runs the following values of the rotational period and peak-to-peak amplitude were estimated for the light curves: 2.637 ± 0.024 h, 0.105 ± 0.007 mag, and 2.616 ± 0.061 h, 0.109 ± 0.018 mag, respectively.