2024-12-09 NASA
This artist’s concept shows interstellar object 1I/2017 U1 (‘Oumuamua) after its discovery in 2017. While itself not a dark comet, ‘Oumuamua’s motion through the solar system has helped researchers better understand the nature of the 14 dark comets discovered so far. European Southern Observatory / M. Kornmesser
＜関連情報＞
- https://www.nasa.gov/solar-system/comets/nasa-researchers-discover-more-dark-comets/
- https://www.pnas.org/doi/10.1073/pnas.2406424121
- https://www.cambridge.org/core/journals/proceedings-of-the-international-astronomical-union/article/direct-detections-of-the-yarkovsky-effect-status-and-outlook/CEA57E9AF5B9F40DCD761061AE59A2D3
暗黒彗星の2つの異なる集団が軌道と大きさで区別される Two distinct populations of dark comets delineated by orbits and sizes
Darryl Z. Seligman, Davide Farnocchia, Marco Micheli,+6, and Karen J. Meech
Proceedings of the National Academy of Sciences Published:December 9, 2024
DOI:https://doi.org/10.1073/pnas.2406424121
Significance
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.
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 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.
ヤルコフスキー効果の直接検出： 現状と展望 Direct Detections of the Yarkovsky Effect: Status and Outlook
Steven R. Chesley,Davide Farnocchia,Petr Pravec and David Vokrouhlický
Proceedings of the International Astronomical Union Published:01 March 2016
DOI:https://doi.org/10.1017/S1743921315008790
Abstract
We report the current results on a comprehensive scan of the near-Earth asteroid catalog for evidence of the Yarkovsky effect in the orbital motion of these bodies. While most objects do not have sufficient observational data to reveal such slight acceleration, we do identify 42 asteroids with a “valid” detection of the Yarkovsky effect, i.e., those with a signal at least 3 times greater than the formal uncertainty and a value compatible with the Yarkovsky mechanism.
We also identify a special category of non-detection, which we refer to as “weak signal,” where the objects are of a size that would permit a clear detection if the Yarkovsky effect is maximized, and yet the orbit is clearly incompatible with such accelerations. The implication is that the Yarkovsky effect is reduced in these cases, presumably due to mid-range obliquity, but possibly also due to size, bulk density, thermal inertia, albedo, or spin rate markedly different from assumptions.
Finally, there are a number of asteroids showing a significant signal for nongravitational acceleration, and yet with a magnitude too great to be attributed to the Yarkovsky effect. We term these “spurious detections” because most are due to erroneous optical astrometry, often involving a single isolated night from precovery observations. Some cases may be due to other nongravitational accelerations, such as outgassing, mass loss, or micro-meteoroid flux.
