Is the Gefion Dynamical Asteroid Family the Source of the L-Chondrites?

Identifying main belt asteroid sources of the ordinary chondrites (H, L, and LL) is a high priority. Ordinary chondrites account for approximately 75% of meteorite falls, of which the L chondrites account for approximately 35% of meteorite falls (Wasson, 1985; Schmitz et al., 2001). From detailed analysis of meteorites, composition and formation environment can be ascertained; pairing the meteorites to probable sources in the main asteroid belt increases our understanding of the compositional and temperature environment during the formation of the inner solar system (Burbine et al., 2002; Gaffey, 2011). Gaffey and Gilbert (1998) identified a probable main belt parent source ((6) Hebe) for the H chondrites and the IIE irons (Burbine et al., 2002; Gaffey and Gilbert, 1998). Probable main belt sources for the L and LL chondrites remain to be confirmed (Burbine et al., 2002). Carruba et al., (2002; 2003), Bottke et al., (2009) and Nesvorny et al., (2009) suggest that the Gefion dynamical asteroid family is the source of the L chondrites (Carruba et al., 2002; Carruba et al., 2003; Bottke et al., 2009; Nesvorny et al., 2009). The age of the Gefion family, taxonomy, and proximity to the 5:2 resonance, coincide with an influx of L chondrites during the middle Ordovician (Schmitz et al., 2001; Schmitz et al., 2003; Bottke et al., 2009; Nesvorny et al., 2009). This study tests the claims of Carruba et al (2002; 2003), Bottke et al., (2009), and Nesvorny et al., (2009) that the Gefion dynamical asteroid family is the source of the L chondrites. Asteroids selected for observation and analysis are members of the Nesvorny Gefion dynamical asteroid family (V2.0) as determined by the Hierarchical Clustering Method (Zappalà et al., 1990; Bendjoya et al., 1993; Bendjoya and Zappala, 2002; Nesvorny, 2012). Visible and near infrared (VNIR, 0.7 to 2.5 μm) spectra of 14 Gefion family asteroids were obtained from the SpeX instrument at the NASA Infrared Telescope Facility (IRTF) 3-meter telescope over several observations during 2011 to 2013 (Rayner et al., 2003). Average spectra were combined with available visible wavelength data from the Small Main-belt Asteroid Spectroscopic Survey, phases I and II, or the Small Solar System Objects Spectroscopic Survey (S3OS2) (Xu et al., 1995, Bus and Binzel, 2002a; 2002b; Lazzaro et al., 2004) to increase wavelength coverage to 0.3 μm (0.5 µm for S3OS2). A search for IRTF spectra of Gefion asteroids in the Small Bodies Database and R. P. Binzel’s asteroid spectroscopy database added one asteroid, (5159) Burbine (Binzel et al., 2014). Mineralogical assemblages were estimated from band parameter analysis and calibrations from Cloutis et al., (1986), Gastineau-Lyons et al., (2002), Gaffey et al (2002), and Dunn et al (2010), of S-type asteroid spectra. Pyroxene chemistry and olivine abundances estimated from band parameters of the S(IV) asteroids via the Gaffey et al., (2002), Gastieau-Lyons et al., (2002), and Dunn et al., (2010) calibrations are not consistent. Only two asteroids, (3910) Liszt and (4182) Mount Locke have assemblages consistent with the L chondrites, there is no dominant mineralogical assemblage, and the Gefion family is not a likely source of the L chondrites.