Cometary activity at 25.7 AU: Hale--Bopp 11 years after perihelion

TL;DR

Eleven years post-perihelion, comet Hale-Bopp exhibited the most distant observed activity at 25.7 AU, consistent with CO-driven activity predictions, revealing persistent dust coma and brightness fading.

Contribution

This study provides the first observation of cometary activity at such a large heliocentric distance, confirming models of CO-driven activity beyond 10 AU.

Findings

Detected a diffuse coma at 25.7 AU, the most distant cometary activity observed.

Brightness and coma properties match predictions for CO-driven activity.

Observed fading in brightness consistent with theoretical models.

Abstract

Eleven years after its perihelion, comet C/1995 O1 (Hale-Bopp) is still active. Between October 20--22, 2007, we detected a diffuse coma of 180x10^3$km in diameter with a slight elongation toward N/S direction. The integrated brightness was 20.04 mag in R_C, implying Af\rho=300 m and albedo x dust surface $a_RC$=4300 km^2. The coma was relatively red at V-R=0.66 mag, which is consistent with that of the dust in other comets. The observed properties and the overall fading in brightness between 10 AU and 26 AU follow the predicted behaviour of CO-driven activity (Capria et al. 2002). This is the most distant cometary activity ever observed.