Isolating the mechanisms for asteroid surface refreshing

TL;DR

This study investigates various mechanisms that could explain the presence of fresh surfaces on asteroids, analyzing spectral data of 477 asteroids to identify trends and suggest multiple processes are involved.

Contribution

It provides a comprehensive spectral analysis of a large asteroid sample, revealing new trends in surface freshness related to size, orbit, and inclination, and emphasizes the need for multiple resurfacing mechanisms.

Findings

Q/S ratio peaks near H=19 and at 5° inclination

Q/S ratio increases with decreasing perihelion distance

Multiple resurfacing mechanisms are likely involved

Abstract

Evidence is seen for young, fresh surfaces among Near-Earth and Main-Belt asteroids even though space-weathering timescales are shorter than the age of the surfaces. A number of mechanisms have been proposed to refresh asteroid surfaces on short timescales, such as planetary encounters, YORP spinup, thermal degradation, and collisions. Additionally, other factors such as grain size effects have been proposed to explain the existence of these "fresh-looking" spectra. To investigate the role each of these mechanisms may play, we collected a sample of visible and near-infrared spectra of 477 near-Earth and Mars Crosser asteroids with similar sizes and compositions - all with absolute magnitude H > 16 and within the S-complex and having olivine to pyroxene (ol/(ol+opx)) ratios > 0.65. We taxonomically classify these objects in the Q (fresh) and S (weathered) classes. We find four trends in the Q/S ratio: 1) previous work demonstrated the Q/S ratio increases at smaller sizes down to H<16, but we find a sharp increase near H=19 after which the ratio decreases monotonically 2) in agreement with many previous studies, the Q/S ratio increases with decreasing perihelion distance, and we find it is non-zero for larger perihelia greater than 1.2AU, 3) as a new finding our work reveals the Q/S ratio has a sharp, significant peak near 5 degrees orbital inclination, and 4) we confirm previous findings that the Q/S ratio is higher for objects that have the possibility of encounter with Earth and Venus versus those that don't, however this finding cannot be distinguished from the perihelion trend. No single resurfacing mechanism can explain all of these trends, so multiple mechanisms are required. It is likely that a combination of all four resurfacing mechanisms are needed to account for all observational trends.