# High Resolution Thermal Infrared Imaging of 3200 Phaethon

## TL;DR

This study used high-resolution thermal infrared imaging to investigate 3200 Phaethon, finding no trapped dust or macroscopic bodies near it and concluding that Geminid meteoroid stream production is not steady.

## Contribution

First high-resolution thermal infrared imaging of 3200 Phaethon at close approach, setting limits on dust presence and mass loss rate, challenging steady-state production models.

## Key findings

- No trapped dust or macroscopic bodies detected within Hill sphere.
- Dust mass loss rate is significantly lower than needed for steady-state Geminid production.
- Limits on dust optical depth are approximately 1e-5.

## Abstract

We present thermal infrared observations of the active asteroid (and Geminid meteoroid stream parent) 3200 Phaethon using the Very Large Telescope. The images, at 10.7 micron wavelength, were taken with Phaethon at its closest approach to Earth (separation 0.07 AU) in 2017 December, at a linear resolution of about 14 km. We probe the Hill sphere (of radius 66 km) for trapped dust and macroscopic bodies, finding neither, and we set limits to the presence of unbound dust. The derived limits to the optical depth of dust near Phaethon depend somewhat on the assumed geometry, but are of order 1e-5. The upper limit to the rate of loss of mass in dust is 14 kg/s. This is about 50 times smaller than the rate needed to sustain the Geminid meteoroid stream in steady state. The observations thus show that the production of the Geminids does not proceed in steady state.