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

Abstract We present the first results from the Cometary Object Study Investigating their Nature and Evolution (COSINE) project, based on a uniformly processed data set of 484 comets observed over the full 15 yr duration of the Wide-field Infrared Survey Explorer (WISE)/NEOWISE mission. This compilation includes 1633 coadded images spanning 966 epochs with signal-to-noise ratios greater than 4, representing the largest consistently analyzed infrared comet data set obtained from a single instrument. Dynamical classification identifies 234 long-period comets (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 μ m) and W2 (4.6 μ m) bands at comparable heliocentric distances. Cometary activity peaks near perihelion, with SPCs exhibiting a pronounced postperihelion asymmetry. Multiepoch photometry reveals that SPCs show steeper brightening and fading slopes than LPCs. The observing geometry of WISE/NEOWISE—constrained to a fixed ∼90° 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.