Searching for parent bodies of differentiated meteorites in the main-belt using visible and near-infrared spectroscopy

Finding a link between meteorites and asteroids thanks to spectroscopy gives a great insight of the composition of the bodies in the asteroid population. Meteorites such as the Howardite-Ensatites-Diogenites (HEDs) have been successfully linked to the asteroid Vesta (McCord et al. (1970), summary by McSween Jr. et al. (2013)), and the ordinary chondrite meteorite population has been connected to a subtype of S-type asteroids, after having taken into account space weathering processes (Binzel et al. 2001). These processes alter the surface of asteroids and modify their reflectance spectra with respect to that of the fresher meteorites, hence they need to be taken into account prior to comparing asteroids with meteorites spectra (Hapke 2001). Other meteorite types have been studied and linked to asteroid types, but some objects still do not show convincing connections (DeMeo et al. 2022). Linking meteorites to the primordial population of objects would give information about the formation and evolution of bodies in the Solar System. Indeed, the planetesimals that formed earliest in the Solar System are thought to have been fully differentiated, due to the melting induced by the heating produced by the radioactive decay of 26Al isotopes. This should have resulted in planetesimals presenting a basaltic crust, an olivine-dominated mantle and an iron-rich core (DeMeo et al. 2019). However most of these primitive objects have evolved, have been disrupted or integrated to other bodies (such as planets) and their formation processes and the composition of their primordial crusts is not well known.

We will report about searching for potential parents bodies of meteorites coming from differentiated planetesimals, using literature data and the new dataset of reflectance spectra that will be released in the Gaia Data Release 3 (DR3) in June 2022. This dataset will present low resolution mean reflectance spectrum of 60 518 Solar System objects, acquired by Gaia’s blue and red spectrophotometers (BP and RP) between August 2014 and May 2017. Each spectrum will consist of 16 discrete wavelength bands that spans the visible wavelength range from 374 to 1034 nm (Gaia collaboration, Galluccio, Delbo et al. 2022). These data should allow to look inside asteroid collisional families and search for hints of differentiation, looking for members corresponding to the crust, mantle or core of a disrupted planetesimal. We intend to use these data to try to link meteorites that are known to have been produced by differentiation (e.g. metallic or andesitic bodies) to the primordial population of asteroids. Finding the parent body of differentiated meteorites would allow to understand better the formation and differentiation of planetesimals in our Solar System.

To compare the reflectance spectra of meteorites with Gaia’s asteroids, we will first use a curve matching method. Curve matching consists in determining whether any given spectrum is similar to a reference spectrum, by the means of a coefficient that has to be minimized (such as the χ2) or maximized (correlation coefficient for example) (Popescu et al. 2012). We will as well study the features of the spectra in order to better characterize the asteroids and validate the matches (Gaffey 2011). Space weathering processes will be taken into account.

Acknowledgements
The authors acknowledge the financial support of CNES and OCA, which make this study possible. M. Delbo thanks financial support from the ANR ORIGINS (ANR-18-CE31-13-0014).

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