Darryl Z. Seligman, Davide Farnocchia, Marco Micheli, and
7 more authors
Dark comets are small bodies with no detected coma that have significant nongravitational accelerations explainable by outgassing of volatiles, analogous to the first interstellar object 1I/’Oumuamua. These objects represent a potentially widespread class of small bodies that further populate the continuum between asteroids and comets and for which the active nature is inferred from their orbital motion. We report detections of seven dark comets which demonstrate that there are two distinct populations based on their orbits and sizes. These objects represent a class of Solar System objects that may have delivered material to the Earth necessary for the development of life such as volatiles and organics. 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 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 classified as inactive (doubling the population) that could also be explainable by asymmetric mass loss. A detailed search of archival survey and targeted data rendered no detection of dust activity in any of these objects in individual or stacked images. We calculate dust production limits of ∼10, 0.1, and 0.1 kg s−1 for 1998 FR11, 2001 ME1, and 2003 RM with these data, indicating little or no dust surrounding the objects during the observations. This set of dark comets reveals the delineation between two distinct populations: larger, “outer” dark comets on eccentric orbits that are end members of a continuum in activity level of comets, and smaller, “inner” dark comets on near-circular orbits that could signify a different different population. These objects may trace various stages in the life cycle of a previously undetected, but potentially numerous, volatile-rich population that may have provided essential material to the Earth.