Superfast Rotating Main-belt Asteroids Discovered in the DECam Ecliptic Exploration Project

Grunnleggende konsepter

Three superfast rotating main-belt asteroids were discovered in a preliminary search of the DECam Ecliptic Exploration Project (DEEP) data, implying a higher incidence rate of such objects than previously measured.

Sammendrag

The DECam Ecliptic Exploration Project (DEEP) is a wide-field solar system survey that is well-suited for detecting superfast rotating main-belt asteroids (SFRs) due to its fast observing cadence and sensitivity to small, subkilometer objects.

In this work, the authors performed a preliminary search for SFRs in a single night of DEEP data, covering 686 main-belt asteroids. They identified three SFRs with rotation periods of 0.21 hours, 0.71 hours, and 0.21 hours. This implies an occurrence rate of 0.4 +0.3/-0.1%, which is higher than the incidence rates measured by previous studies.

The authors suggest that this high occurrence rate is due to DEEP's sensitivity to the small, subkilometer size regime, which is thought to be dominated by rubble pile asteroids. They compute the minimum required cohesive strengths for each of the three SFRs, finding values ranging from ~100 to ~10,000 Pa. These strengths are more than that of weak regolith but consistent with many cohesive asteroid strengths reported in the literature.

The authors note that the full DEEP survey has measured over 60,000 main-belt asteroid lightcurves, and they expect to identify ~300 SFRs across the entire data set. This will provide a robust distribution of required cohesive strengths within the main belt, which can probe the interior structure and collisional history of these objects.

Statistikk

The three SFRs have rotation periods of 0.21 hours, 0.71 hours, and 0.21 hours.
The estimated diameters of the three SFRs are 0.5 +0.2/-0.5 km, 0.4 +0.25/-0.5 km, and 0.3 +0.15/-0.6 km, respectively.

Sitater

"Superfast rotators (SFRs) are small solar system objects that rotate faster than generally possible for a cohesionless rubble pile."
"We find that all three of these SFRs require strengths that are more than that of weak regolith but consistent with many cohesive asteroid strengths reported in the literature."
"Across the full DEEP data set, we have identified ∼70,000 Main-Belt Asteroids and expect ∼300 SFRs—a result that will be assessed in a future paper."

Viktige innsikter hentet fra

The DECam Ecliptic Exploration Project (DEEP). VII. The Strengths of Three Superfast Rotating Main-belt Asteroids from a Preliminary Search of DEEP Data

by Ryder Straus... klokken arxiv.org 10-03-2024

https://arxiv.org/pdf/2410.01147.pdf

Dypere Spørsmål

How do the incidence rates of SFRs compare between main-belt asteroids and near-Earth objects, and what implications would this have for the dominant spin-up mechanisms (YORP vs. collisions)?

The incidence rates of superfast rotators (SFRs) in main-belt asteroids (MBAs) and near-Earth objects (NEOs) present intriguing contrasts that can inform our understanding of the dominant spin-up mechanisms at play. In the DECam Ecliptic Exploration Project (DEEP), the observed incidence rate of SFRs among MBAs was approximately 0.4%, which is significantly higher than the rates reported in previous studies, where less than 0.1% of rubble-pile asteroids were found to have rotation periods shorter than the 2.2-hour spin barrier. This suggests that the DEEP survey's sensitivity to smaller sub-kilometer asteroids may have contributed to this enhanced detection rate.
In contrast, NEOs, which are more susceptible to thermal effects due to their proximity to the Sun, may exhibit different spin-up dynamics. The Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect, which is a thermal radiation-driven torque, is particularly effective for smaller bodies and is expected to play a significant role in the spin-up of NEOs. Given that NEOs are often subjected to more frequent and intense thermal cycling, they may have a higher incidence of SFRs compared to MBAs if YORP is the dominant mechanism.
If the incidence rates of SFRs are found to be similar between NEOs and MBAs, it would imply that collisional processes, which are more prevalent in the main belt, could be the primary driver of spin-up for both populations. Conversely, if NEOs show a significantly higher incidence of SFRs, it would suggest that YORP is the more influential mechanism for these objects. This distinction is crucial for understanding the evolutionary pathways of asteroids and their potential for becoming hazardous objects as they transition from the main belt to near-Earth space.

What are the potential mechanisms that could produce the high cohesive strengths required for the observed SFRs, and how do these relate to the interior structure and composition of rubble pile asteroids?

The high cohesive strengths required for the observed SFRs can be attributed to several potential mechanisms that influence the interior structure and composition of rubble pile asteroids. One primary mechanism is the presence of inter-particle cohesion, which can arise from various physical processes, including van der Waals forces, electrostatic interactions, and the effects of fine-grained materials that can act as a binding agent. These cohesive forces allow rubble pile asteroids, which are typically composed of loosely bound aggregates of smaller rocks and debris, to maintain structural integrity even at high rotation rates.
Another potential mechanism is the existence of a monolithic structure, where the asteroid is a solid fragment from a larger parent body. Such a structure would inherently possess greater cohesive strength than a typical rubble pile, allowing for faster rotation without disintegration. However, the formation of such monolithic bodies in the current collisional environment of the main belt poses challenges, as these fragments would likely have undergone multiple disruption events over the solar system's history.
Additionally, the cohesive strength of rubble piles may be influenced by the distribution of grain sizes within the asteroid. Smaller particles can effectively "cement" larger boulders together, enhancing the overall cohesive strength. This grain-size dependence suggests that the internal composition of rubble pile asteroids is heterogeneous, with varying degrees of cohesion depending on the local material properties.
Understanding these mechanisms is essential for interpreting the observed rotational characteristics of SFRs and their implications for the evolutionary history of asteroids. The cohesive strengths derived from the lightcurve analysis of SFRs provide insights into the internal structure of these bodies, indicating that many rubble piles may possess significant internal cohesion, contrary to the traditional view of them as entirely strengthless aggregates.

How can the distribution of required cohesive strengths for SFRs across the main belt be used to infer information about the collisional and evolutionary history of this population?

The distribution of required cohesive strengths for SFRs across the main belt serves as a valuable tool for inferring the collisional and evolutionary history of this population. By analyzing the cohesive strengths derived from the lightcurve data of SFRs, researchers can gain insights into the internal structure and composition of these asteroids, which in turn reflects their formation and evolution.
A broad range of cohesive strengths, as observed in the DEEP study, suggests a diverse population of asteroids with varying internal properties. This diversity can be indicative of different collisional histories, where some asteroids may have experienced significant impacts that altered their internal structure, while others may have remained relatively intact. For instance, asteroids with higher cohesive strengths may have undergone fewer disruptive collisions, allowing them to maintain their structural integrity and resist breakup at high rotation rates.
Moreover, the cohesive strength distribution can provide clues about the size and composition of the parent bodies from which these asteroids originated. If a significant number of SFRs exhibit cohesive strengths that exceed those typical of weak regolith, it may imply that these bodies are remnants of larger, more coherent parent bodies that fragmented due to past collisions. Conversely, a prevalence of lower cohesive strengths could suggest a population dominated by smaller, more loosely bound rubble piles.
Additionally, the relationship between cohesive strength and grain size distribution within these asteroids can inform researchers about the processes that have shaped their surfaces and interiors over time. For example, the presence of fine-grained materials that enhance cohesion may indicate a history of space weathering or other surface processes that have contributed to the current state of the asteroid population.
In summary, the analysis of cohesive strengths among SFRs not only enhances our understanding of individual asteroids but also provides a broader context for the collisional and evolutionary dynamics of the main belt as a whole. This information is crucial for developing models of asteroid formation, evolution, and the potential hazards they may pose to Earth.