Two Distinct Populations of Dark Comets Delineated by Orbits and Sizes
Darryl Z. Seligman, Davide Farnocchia, Marco Micheli, Olivier R. Hainaut, Henry H. Hsieh, Adina D. Feinstein, Steven R. Chesley, Aster G. Taylor, Joseph Masiero, Karen J. Meech

TL;DR
This study identifies two distinct populations of dark comets with different orbital and size characteristics, revealing potential stages in the life cycle of a volatile-rich population that contributed to Earth's water.
Contribution
It uncovers a new classification of dark comets based on orbit and size, suggesting different activity levels and evolutionary stages.
Findings
Detected nongravitational accelerations on seven inactive objects.
No dust activity was observed in archival images for these objects.
Large, eccentric dark comets form one population, smaller, near-circular dark comets form another.
Abstract
Small bodies are capable of delivering essential prerequisites for the development of life, such as volatiles and organics, to the terrestrial planets. For example, empirical evidence suggests that water was delivered to the Earth by hydrated planetesimals from distant regions of the Solar System. Recently, several morphologically inactive near-Earth objects (NEOs) were reported to experience significant nongravitational accelerations inconsistent with radiation-based effects, and possibly explained by volatile-driven outgassing. However, these "dark comets" display no evidence of comae in archival images, which are the defining feature of cometary activity. Here we report detections of nongravitational accelerations on seven additional objects previously classified as inactive (doubling the population) that could also be explainable by asymmetric mass loss. A detailed search of…
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