# Active asteroid (6478) Gault: a blue Q-type surface below the dust?

## TL;DR

This study uses near-infrared spectroscopy to analyze asteroid (6478) Gault, revealing spectral variability and suggesting surface exposure of fresh material due to dust loss, with implications for understanding its activity and composition.

## Contribution

It provides the first detailed spectral analysis of Gault, linking its surface properties to dust loss and activity, and proposes a connection to its collisional family.

## Key findings

- Gault is a silicate-rich Q- or S-type asteroid.
- Spectral slope varies from blue to red, unrelated to activity.
- Blue spectra indicate exposure of fresh, dust-free surface material.

## Abstract

We present near-infrared spectroscopy of the sporadically active asteroid (6478) Gault collected on the 3 m NASA/Infrared Telescope Facility observatory in late 2019 March/early April. Long-exposure imaging with the 0.5 m NEEMO T05 telescope and previously published data simultaneously monitored the asteroid activity, providing context for our measurements. We confirm Gault is a silicate-rich (Q- or S-type) object likely linked to the (25) Phocaea collisional family. The asteroid exhibits substantial spectral variability over the 0.75-2.45 $\mu$m wavelength range, from unusual blue (s'=-13.5+/-1.1% $\mu$m-1 to typical red (s'=+9.1+/-1.2% $\mu$m-1) spectral slope, that does not seem to correlate with activity. Spectral comparisons with samples of ordinary chondrite meteorites suggest that the blue color relates to the partial loss of the asteroid dust regolith, exposing a fresh, dust-free material at its surface. The existence of asteroids rotating close to rotational break-up limit and having similar spectral properties as Gault further supports this interpretation. Future spectroscopic observations of Gault, when the tails dissipate, will help further testing of our proposed hypothesis.