The potentially hazardous Asteroid (214869) 2007 PA8: An unweathered L chondrite analog surface

Abstract

In this paper we present the results on the polarimetric and spectroscopic observations of the potentially hazardous Asteroid (214869) 2007 PA8 obtained during its favorable apparition in October–November 2012, when it approached the Earth at the minimal distance of 0.043AU. Polarimetry was carried out at the NOT in the B, V, R, and I bands covering both low (12–23°) and large phase angles (88–99°). Spectroscopy in the visible and near infrared range was obtained at the TNG telescope.The spectrum of 2007 PA8 shows silicates absorption features and a behavior consistent with a Q-type classification. The olivine and pyroxene BI band is centered at 0.9578±0.0042μm, with a band depth of 16.5%, the BII band is centered at 1.95±0.01μm, and it has a band depth of about 3.9%. The 2007 PA8 spectral parameters are consistent with those of L chondrites. Also the spectral comparison with meteorites gives the L-type chondrites, and L6 in particular, as best match.The NEA (214869) 2007 PA8 is the forth moderate albedo asteroid and the first Q-type asteroid for which the value of the polarization maximum is determined. The inversion angle of the polarization curve in the V filter is 19.0±1.1°, the corresponding slope parameter (h) is of 0.078±0.010%/°, the maximum value of polarization is 5.99±0.16%, and the extreme value of negative polarization is estimated to be lower than −0.52%. Using the polarimetric slope we derive a geometric albedo of 0.29±0.08 in the V band, that gives an estimated diameter of 1.4±0.2km, assuming an absolute Hv magnitude of 16.2mag. We find a strong dependence of the polarization in the B, V, R, and I bands with wavelength, and the polarimetric albedo in the four bands is strongly correlated with the asteroid’s spectrum. The 2007 PA8 polarimetric properties resemble those of other 2 NEAs, 1566 Icarus and 25143 Itokawa, which are both S(IV)/Q type.Our spectral and polarimetric analysis indicate that 2007 PA8 has a young and fresh surface almost unweathered, similar to L-type chondrites. These results, together with dynamical simulations made by Nedelcu et al. (Nedelcu, D. A., Birlan, M., Popescu, M., Badescu, O., Pricopi, D. [2014]. Astron. Astrophys. 567, L7, 5pp.) and Nesvorny et al. (Nesvorny, D., Vokrouhlicky, D., Morbidelli, A., Bottke, W. F. [2009]. Icarus 200, 698–701), indicate that 2007 PA8 may be a member of the Gefion family recently ejected from the 5:2 resonance and a potential source of L chondrites.