Testing The Gefion Family As A Possible Parent Body For The L-Chondrite Meteorites

The L-chondrite meteorites are the most abundant meteorites falling to Earth. Identifying a parent body for them has been an important goal of asteroid science for more than thirty years. A link between the two could help to decipher the history of thermal regimes and evolutionary processes that occurred in the early solar system. A plausible or probable parent body can be identified based on two main criteria. A plausible body will either be located favorably to deliver the relevant amounts of meteoroids to the Earth, or will possess a surface mineralogy compatible with that of the L-chondrite meteorites. A probable parent body will meet both criteria (Gaffey, 2011). Based on research performed on fossil L-chondrite meteorites, and dynamical modeling of various resonances and asteroid families, the Gefion family has been hypothesized as a plausible source of the L-chondrite meteorites. It is favorably located within the asteroid belt for delivery of fragments to Earth, so in an effort to test the possibility that this family is a probable parent to these meteorites, this study used near-infrared spectral data gathered with the NASA Infrared Telescope Facility (IRTF) to characterize the mineralogy of two asteroids of the Gefion Family. Although not solidly proven to be L-chondrites, both asteroids are grossly consistent with the mineralogy of this type of meteorite. Taking error into account, whether human, meteorological, or instrumental, both asteroids can reasonably be considered to fall within the L-chondrite realm. More spectra of these and other Gefion asteroids are needed to come to a valid conclusion regarding the family as a source for these meteorites, but at this point the hypothesis is still a viable one

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