Origins of colors variability among C-cluster main-belt asteroidsOPEN ACCESS 

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Pierre Beck, Olivier Poch

Icarus
Available online: 21 April 2021

LINK

Update (6 May 2021): PDF (OPEN ACCESS)

“Highlights

• A C-type cluster is identified by an SDSS colors & albedo cluster analysis.
• The C-cluster matches CM chondrites but generally not other type of CC.
• Small C-type MBAs appear bluer (<20 km) than large ones (D > 20 km).
• We suggest that bluer objects are covered by larger grained material (>mm to rocks).”

“The Sloan Digital Sky Survey provides colors for more than 100,000 moving objects, among which around 10,000 have albedos determined. Here we combined colors and albedo in order to perform a cluster analysis on the small bodies population, and identify a C-cluster, a group of asteroid related to C-type as defined in earlier work. Members of this C-cluster are in fair agreement with the color boundaries of B and C-type defined in DeMeo and Carry (2013). We then compare colors of C-cluster asteroids to those of carbonaceous chondrites powders, while taking into account the effect of phase angle. We show that only CM chondrites have colors in the range of C-cluster asteroids, CO, CR and CV chondrites being significantly redder. Also, CM chondrites powders are on average slightly redder than the average C-cluster. The colors of C-cluster members are further investigated by looking at color variations as a function of asteroid diameter. We observe that the visible slope becomes bluer with decreasing asteroids diameter, and a transition seems to be present around 20 km. We discuss the origin of this variation and, if not related to a bias in the dataset – analysis, we conclude that it is related to the surface texture of the objects, smaller objects being covered by rocks, while larger objects are covered by a particulate surface. The blueing is interpreted by an increased contribution of the first reflection in the case of rock-dominated surfaces, which can scatter light in a Rayleigh-like manner. We do not have unambiguous evidence of space weathering within the C-cluster based on this analysis, however the generally bluer nature of C-cluster objects compared to CM chondrites could be to some extent related to space weathering.”

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