COSINE (Cometary Object Study Investigating their Nature and Evolution) I. Project Overview and General Characteristics of Detected Comets

TL;DR

This study analyzes 484 comets observed over 15 years by WISE/NEOWISE, revealing differences in brightness, activity, and evolution between long- and short-period comets, and establishing a foundation for future detailed analyses.

Contribution

First uniform infrared dataset of 484 comets from WISE/NEOWISE, providing insights into their brightness, activity, and evolutionary trends across populations.

Findings

LPCs are statistically brighter than SPCs at similar distances.

Comet activity peaks near perihelion with asymmetry in SPCs.

SPCs show steeper brightness change slopes than LPCs.

Abstract

We present the first results from the COSINE (Cometary Object Study Investigating their Nature and Evolution) project, based on a uniformly processed dataset of 484 comets observed over the full 15-year duration of the WISE/NEOWISE mission. This compilation includes 1,633 coadded images spanning 966 epochs with signal-to-noise ratios (S/N) greater than 4, representing the largest consistently analyzed infrared comet dataset obtained from a single instrument. Dynamical classification identifies 234 long-period (LPCs) and 250 short-period comets (SPCs), spanning heliocentric distances of 0.996--10.804 au. LPCs are statistically brighter than SPCs in the W1 (3.4 um) and W2 (4.6 um) bands at comparable heliocentric distances. Cometary activity peaks near perihelion, with SPCs exhibiting a pronounced post-perihelion asymmetry. Multi-epoch photometry reveals that SPCs show steeper brightening and fading slopes than LPCs. The observing geometry of WISE/NEOWISE -- constrained to a fixed ~90-deg solar elongation from low-Earth orbit -- introduces systematic biases in the sampling of orientation angles for extended features. Collectively, the results reveal a continuous evolutionary gradient across comet populations, likely driven by accumulated solar heating and surface processing. This study establishes a foundation for subsequent COSINE analyses, which will separate nucleus and coma contributions and model dust dynamics to further probe cometary activity and evolution.