Gaia spectroscopic view of asteroid collisional families: preliminary results

The Gaia mission of the European Space Agency (ESA) was launched in December 2013 and began it scientific operations in July 2014. Gaia is essentially devoted to the measurement  of positions, parallaxes, proper motions, brightnesses, and colours of stars. However, Gaia has also obtained astrometric, photometric, and spectroscopic measurements for several hundreds of thousands of asteroids. 

The Gaia Data Release 3 (DR3) is the first to contain low resolution reflectance spectra of 60,518 solar system small bodies, the large majority of which are asteroids of the main belt (Gaia collaboration, Galluccio, Delbo et al. 2022). The global survey properties, the methods of data production and validation are detailed in the aforementioned paper published by the journal Astronomy and Astrophysics, which accompanies the DR3, and also summarised in the presentation of Galluccio et al. (2022) at this conference (EPSC 2022). 

Here we present preliminary results about the Gaia view of asteroid collisional families. We identified asteroids belonging to families during the validation of Gaia asteroid spectra. Based on the family identification of Nesvorny et al. (2015), with the addition of the New Polana and the Eulalia families from Walsh et al. (2013), we found that in the Gaia DR3 there are 25,088 asteroids that belong to 116 collisional asteroid families of the 121 listed in Tab.1. This table also reports the number of family members and the number of members with a Gaia DR3 reflectance spectrum. However, the family identification of current catalogues is conservative by construction in order to keep good separation between the families. Hence, it is very likely that (i) some of the known families are more extended than what is available in current catalogues, namely, that catalogues based on dynamical criteria do not capture the whole extent of a family, and (ii) some unknown families are yet to be identified. This implies that the aforementioned number of asteroid family members with Gaia DR3 reflectance spectra is likely an estimation lower than the true number. 

We will present some important features that Gaia observed in families. One of these is the correlation between some spectral parameters, such as the slope and the depth of the 1-micron absorption band of the reflectance spectrum, and the age of members of asteroid families belonging to the so called spectroscopic S-complex (DeMeo et al. 2009). These correlations can be explained in terms of a space weathering process that reddens and reduces the 1-band depth as a function of time on S-complex asteroids.

For the brightest asteroids, the extension of Gaia reflectance spectra at wavelengths shorter than 0.45 micron is very useful for distinguishing the composition of primitive, carbonaceous asteroid families, which are difficult to be discriminated with the ground based spectroscopic data currently present in the literature. 

References:

- DeMeo, F. E., Binzel, R. P., Slivan, S.~M., Bus, S. J. 2009. Icarus 202, 160–180.

- Gaia collaboration, Galluccio, Delbo et al. 2022. A&A under review. 

- Nesvorný, D., Brož, M., & Carruba, V. 2015.  in Asteroids IV (P. Michel, et al. eds.) University of Arizona Press, Tucson.,

- Walsh, K. J., Delbo, M., et al. 2013. Icarus 225, 283–297.