Comet 240P/NEAT is Stirring

TL;DR

This study analyzes the long-term activity and brightening events of comet 240P/NEAT, revealing that increased solar heating after Jupiter perturbation causes localized, sustained activity increases, shedding light on comet surface evolution.

Contribution

It provides the first detailed analysis of long-lived brightening events in comet 240P/NEAT and links these to orbital perturbations and surface heterogeneity.

Findings

Three long-lived brightening events observed over three orbits.

Brightening likely caused by increased insolation warming subsurface layers.

Surface activity is localized and heterogeneous.

Abstract

Comets are primitive objects that formed in the protoplanetary disk, and have been largely preserved over the history of the Solar System. However, they are not pristine, and surfaces of cometary nuclei do evolve. In order to understand the extent of their primitive nature, we must define the mechanisms that affect their surfaces and comae. We examine the lightcurve of comet 240P/NEAT over three consecutive orbits, and investigate three events of significant brightening ($\Delta m \sim -2$ mag). Unlike typical cometary outbursts, each of the three events are long-lived, with enhanced activity for at least 3 to 6 months. The third event, observed by the Zwicky Transient Facility, occurred in at least two stages. The anomalous behavior appears to have started after the comet was perturbed by Jupiter in 2007, reducing its perihelion distance from 2.53 to 2.12 au. We suggest that the brightening events are temporary transitions to a higher baseline activity level, brought on by the increased insolation, which has warmed previously insulated sub-surface layers. The new activity is isolated to one or two locations on the nucleus, indicating that the surface or immediate sub-surface is heterogeneous. Further study of this phenomenon may provide insight into cometary outbursts, the structure of the near-surface nucleus, and cometary nucleus mantling.