Asteroid age distributions determined by space weathering and collisional evolution models

TL;DR

This study combines dynamical and color evolution models to estimate asteroid surface ages, revealing characteristic weathering and gardening timescales for S-complex asteroids based on a sample of 95 objects.

Contribution

It introduces an integrated approach using space weathering and collisional models to determine asteroid surface ages from color and size data, refining previous models with empirical data.

Findings

Characteristic weathering time: 2050 Myr

Characteristic gardening time: 4400 Myr

Predicted fresh surface color matches observed chondritic surfaces

Abstract

We provide evidence of consistency between the dynamical evolution of main belt asteroids and their color evolution due to space weathering. The dynamical age of an asteroid's surface \citep{bib.bot05a,bib.nes05} is the time since its last catastrophic disruption event which is a function of the object's diameter. The age of an S-complex asteroid's surface may also be determined from its color using a space weathering model \citep[e.g.][]{bib.wil10,bib.jed04,bib.wil08,bib.mar06}. We used a sample of 95 S-complex asteroids from SMASS and obtained their absolute magnitudes and $u,g,r,i,z$ filter magnitudes from SDSS. The absolute magnitudes yield a size-derived age distribution. The $u,g,r,i,z$ filter magnitudes lead to the principal component color which yields a color-derived age distribution by inverting our color-age relationship, an enhanced version of the `dual $\tau$' space weathering model of \citet{bib.wil10}. We fit the size-age distribution to the enhanced dual $\tau$ model and found characteristic weathering and gardening times of $\tau_w = 2050 \pm 80$ Myr and $\tau_g = 4400^{+700}_{-500}$ Myr respectively. The fit also suggests an initial principal component color of $-0.05 \pm 0.01$ for fresh asteroid surface with a maximum possible change of the probable color due to weathering of $\Delta PC = 1.34 \pm 0.04$. Our predicted color of fresh asteroid surface matches the color of fresh ordinary chondritic surface of $PC_1 = 0.17 \pm 0.39$.