The Dynamical Origins of the Dark Comets and a Proposed Evolutionary Track (2407.01839v1)

Abstract: So-called 'dark comets' are small, morphologically inactive near-Earth objects (NEOs) that exhibit nongravitational accelerations inconsistent with radiative effects. These objects exhibit short rotational periods (minutes to hours), where measured. We find that the strengths required to prevent catastrophic disintegration are consistent with those measured in cometary nuclei and expected in rubble pile objects. We hypothesize that these dark comets are the end result of a rotational fragmentation cascade, which is consistent with their measured physical properties. We calculate the predicted size-frequency distribution for objects evolving under this model. Using dynamical simulations, we further demonstrate that the majority of these bodies originated from the $\nu_6$ resonance, implying the existence of volatiles in the current inner main belt. Moreover, one of the dark comets, (523599) 2003 RM, likely originated from the outer main belt, although a JFC origin is also plausible. These results provide strong evidence that volatiles from a reservoir in the inner main belt are present in the near-Earth environment.

• The paper analyzes dark comets, a distinct population of inactive near-Earth objects that exhibit non-gravitational accelerations indicative of cometary activity.
• The authors propose a rotational fragmentation cascade as a likely evolutionary path, explaining their small size, rapid rotation, and resistance to further breakup.
• Dynamical simulations suggest origins primarily from the ν6 resonance in the inner main belt, highlighting dark comets as a potentially significant and under-recognized class of extinct comets among NEOs.

The Dynamical Origins of Dark Comets: A Comprehensive Analysis

The paper, "The Dynamical Origins of the Dark Comets and a Proposed Evolutionary Track," authored by Aster G. Taylor et al., provides an in-depth analysis of a unique population of small, inactive near-Earth objects (NEOs) known as "dark comets." These objects exhibit non-gravitational accelerations that align with cometary activity but lack discernible cometary comae. The research outlines strong evidence that dark comets are not simply asteroids, despite their physical inactivity, and categorizes them as a distinct class within the loosely defined asteroid-comet continuum.

Key Findings and Theoretical Implications

1. Physical and Dynamical Characteristics: Dark comets typically have small sizes, rapid rotations, and non-radial accelerations that are atypical for asteroids. Their strengths prevent catastrophic disintegration, aligning more closely with cometary nuclei or rubble pile objects than with traditional asteroids.
2. Rotational Fragmentation Cascade Hypothesis: The authors propose that dark comets might result from a rotational fragmentation cascade. This process involves an initial rotational fission due to sublimation-driven spin-up, resulting in successive fragmentation into smaller, more stable objects. As these fragments evolve, their rapid rotations and small scales contribute to their resistance to further breakup.
3. Origin and Evolution: Using dynamical simulations, the research suggests that most dark comets originate from the ν6 resonance, indicating a source of volatiles in the inner main belt. While about 60% of the observed dark comets could have evolved from the ν6 region, a minority, such as the notably distinct (523599) 2003 RM, may have origins in the outer main belt.
4. Temporal Dynamics and Stability: The paper predicts the size-frequency distribution of these comets, showing that smaller, faster-rotating fragments become increasingly stable over time as they lose mass and volatiles.
5. Consequences for Near-Earth Space: This paper underscores a potentially significant population of dead or extinct cometary fragments in near-Earth space. These fragments, while difficult to detect due to their small size and low albedo, could constitute a non-negligible portion of the small NEO population.
6. Ambiguous Classifications: The report highlights that many NEOs traditionally cataloged as asteroids due to a lack of observed activity might belong to this category of dark comets. Existing models, such as NEOMOD, can be adapted to account for these findings, suggesting a reconceptualization of NEO classification is needed.

Practical and Future Outlook

The comprehensive framework outlined in this paper reveals new pathways for understanding the dynamic processes in the asteroid belt and the delivery of material to the inner solar system. This work prompts further investigation into:

• Search for Additional Dark Comets: Future survey missions might enable the detection of more dark comets, refining constraints on their population and dynamical properties.
• Remote Observations and Missions: Observational campaigns, perhaps involving space missions such as Hayabusa2, could provide direct insights into their composition, structure, and dynamics.
• Improved Dynamical Models: Enhanced simulations that incorporate these findings might improve our understanding of small body dynamics, particularly concerning rotationally and tidally driven processes.

Overall, the paper by Taylor et al. makes significant contributions to planetary science by characterizing dark comets, elucidating their potential origins, and proposing a credible evolutionary mechanism. The implications of this work refine our understanding of NEO classification and pave the way for novel insights into the solar system's early history and material transport processes.