Space Weathering Signatures in Asteroid Families of Different Taxonomic Types

Space weathering is one of the key processes controlling the spectral evolution of airless bodies in the Solar System. Laboratory experiments, lunar sample studies, and spacecraft missions demonstrated that solar-wind and cosmic rays’ irradiation and micrometeoroid bombardment progressively alter the optical properties of the regolith, leading to variations in spectral slope, overall darkening, and attenuation of diagnostic absorption bands. [1,4,6,7,16]. These effects are especially significant for asteroid research, as they influence both the interpretation of taxonomic classes and the correspondence between asteroid spectra and meteorite samples. Asteroid families provide a natural laboratory for investigating the long-term evolution of space weathering because the members of one family share a common origin, similar composition, and comparable age [13,14].

Methodology

In this work we investigate manifestations of space weathering among asteroid families of different taxonomic types using large photometric surveys. The analysis is based on 24 asteroid families, including S-type families (Agnia, Barcelona, Eunomia, Gefion, Iannini, Karin, Koronis, Maria, Massalia, Merxia, and Rafita) and C-type families (Adeona, Astrid, Dora, Erigone, Euphrosyne, Hoffmeister, Hygiea, Misa, Naema, Nemesis, Themis, Ursula, and Veritas) and V-type Vesta family. Photometric data were taken from the SDSS MOC4 catalog together with the new reprocessed SDSS data [16], calculated from Gaia DR3 spectra [5], and SkyMapper catalogs [17]. The use of several independent surveys allowed us to compare the consistency of color trends and reduce systematic effects.

To estimate family ages we applied the V-shape method in the space of proper semimajor axis versus absolute magnitude (a–H) [2,13]. The V-shape boundaries were fitted for each family individually, taking into account the Yarkovsky-driven spreading of fragments [2]. Family ages were calculated using semiempirical relations based on the V-shape width, geometric albedo from WISE [12], and mean density values for different taxonomic classes from Carry [3]. The obtained ages range from several Myr for young families such as Iannini and Karin to more than 1 Gyr for evolved families such as Koronis and Maria.

The main indicator of space weathering in this study is the photometric parameter a*, originally introduced for SDSS asteroid taxonomy [8]. This parameter is sensitive to the spectral slope and therefore can be used as a proxy for spectral reddening. For each family we cross-matched all available members with the four photometric catalogs and calculated mean color indices and a* values. Additional filtering based on geometric albedo and color distribution was applied to remove interlopers and improve taxonomic homogeneity. The SDSS and SkyMapper surveys also provide an opportunity to analyze the behavior of color indices in the near-ultraviolet region. In particular, the u − g and u − v color indices from these two surveys were used after excluding measurements with large errors. In addition, correlations between the color indices and the sizes of asteroids were investigated for the selected families.

 

Results

Our analysis reveals a clear correlation between the a* parameter and the logarithm of family age for S-type asteroid families. The observed trend shows rapid reddening during the first several hundred Myr, followed by a slower phase of spectral evolution. Such behavior is consistent with earlier SDSS-based studies of asteroid space weathering [10, 13] and with laboratory simulations of irradiated silicate materials [9, 15]. The trend is reproduced independently in all four photometric catalogs, indicating that the observed effect is robust.

In contrast, C-type asteroid families demonstrate a different evolutionary behavior: average a* parameter decreases with increasing age. The correlation is weaker than for S-type objects, but the same tendency appears in all analyzed datasets. Unlike silicate-rich S-type asteroids, carbonaceous surfaces may experience slower or compositionally different weathering processes [11].

Another evolutionary effect observed in asteroid families is the change of the lightcurve amplitudes with age. Most asteroid families display amplitude distributions peaking at 0.25–0.35 mag, with preferred rotation periods concentrated near 5, 10, and 15 h. A weak negative correlation was found between mean lightcurve amplitude and family age. Several young families exhibit significantly larger amplitudes than families of comparable age.

Conclusions
The obtained results confirm that broad-band photometric surveys can be successfully used to study long-term spectral evolution of asteroid surfaces. The combination of V-shape dating and photometric indicators provides an efficient approach for investigating space weathering in large asteroid populations. The different behavior observed for S- and C-type families demonstrates that the mechanisms and timescales of space weathering are taxonomically dependent and should be considered separately in models of asteroid surface evolution.

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