Space weathering of the 3-μm phyllosilicate feature induced by pulsed laser irradiation

Abstract

Here we present results from pulsed laser irradiation of CI and CM simulant samples in an effort to simulate space weathering on airless bodies via micrometeorite impacts. For this study, we focused on determining what type of alteration occurs in the 3-μm absorption region, as this region will be critical to ascertain compositional information of the surface regolith on hydrated asteroids. Generally, using entirely in situ spectral analysis, we find that the laser produces similar effects in both samples. Specifically, irradiation causes the blue spectral slope to increase until it is relatively flat. Furthermore, the sample darkens initially with laser irradiation but brightens back to about half of its original level by the end of the irradiation. We also find that laser irradiation causes the band depth on the 3-μm absorption band to increase by as much as 30%, yet the shape of the entire absorption band does not change and the band minima of the 2.72 μm shifts less than 0.001 μm as a result of laser irradiation. The constancy of the latter two parameters, which will be most critical to compositional analysis, suggests that this spectral region could be very useful to determine the asteroid composition on surfaces of hydrated asteroids that have undergone extensive aqueous alteration even if the surface had been subject to a significant amount of space weathering. Whether the same conclusion will be generally applicable to other surfaces containing minerals with a wide range of aqueous alteration is currently unclear but will be tested in future studies.