# Physical Characterization of Active Asteroid (6478) Gault

## TL;DR

This study characterizes the physical and compositional properties of active asteroid (6478) Gault using photometric, spectroscopic, and thermal data, revealing its S-type composition and linking it to the Phocaea family.

## Contribution

It provides new physical and compositional data on Gault, clarifying its asteroid family association and physical characteristics for the first time.

## Key findings

- Gault has a diameter less than 6 km.
- Spectroscopy shows Gault is similar to S-complex asteroids and H chondrites.
- No evidence of fresh material exposure during outbursts.

## Abstract

Main belt asteroid (6478) Gault has been dynamically linked with two overlapping asteroid families: Phocaea, dominated by S-type asteroids, and Tamara, dominated by low-albedo C-types. This object has recently become an interesting case for study, after images obtained in late 2018 revealed that it was active and displaying a comet-like tail. Previous authors have proposed that the most likely scenarios to explain the observed activity on Gault were rotational excitation or merger of near-contact binaries. Here we use new photometric and spectroscopic data of Gault to determine its physical and compositional properties. Lightcurves derived from the photometric data showed little variation over three nights of observations, which prevented us from determining the rotation period of the asteroid. Using WISE observations of Gault and the near-Earth Asteroid Thermal Model (NEATM) we determined that this asteroid has a diameter $<$6 km. NIR spectroscopic data obtained with the Infrared Telescope Facility (IRTF) showed a spectrum similar to that of S-complex asteroids, and a surface composition consistent with H chondrite meteorites. These results favor a compositional affinity between Gault and asteroid (25) Phocaea, and rules out a compositional link with the Tamara family. From the spectroscopic data we found no evidence of fresh material that could have been exposed during the outburst episodes.