Comet Fading Begins Beyond Saturn

TL;DR

This study uses numerical simulations to reveal that many long-period comets fade during distant passages beyond Saturn, leading to underestimation of their true population and evolution.

Contribution

It demonstrates that comet fading occurs at greater distances than previously thought, affecting detection and understanding of LPCs' physical and dynamical properties.

Findings

Many LPCs fade before reaching Saturn, eluding detection.

Comet properties evolve significantly at distances beyond 10 au.

Detection biases impact our understanding of LPC populations.

Abstract

The discovery probability of long-period comets (LPCs) passing near the Sun is highest during their first passage and then declines, or fades, during subsequent return passages. Comet fading is largely attributed to devolatilization and fragmentation via thermal processing within 2-3 au of the Sun (1 au being the Earth-Sun distance). Here our numerical simulations show that comet observing campaigns miss vast numbers of LPCs making returning passages through the Saturn region (near 10 au) because these comets fade during prior, even more distant passages exterior to Saturn and thus elude detection. Consequently, comet properties significantly evolve at solar distances much larger than previously considered, and this offers new insights into the physical and dynamical properties of LPCs, both near and far from Earth.