Main Belt Asteroids with WISE/NEOWISE I: Preliminary Albedos and Diameters (1109.4096v1)

Abstract: We present initial results from the Wide-field Infrared Survey Explorer (WISE), a four-band all-sky thermal infrared survey that produces data well suited to measuring the physical properties of asteroids, and the NEOWISE enhancement to the WISE mission allowing for detailed study of Solar system objects. Using a NEATM thermal model fitting routine we compute diameters for over 100,000 Main Belt asteroids from their IR thermal flux, with errors better than 10%. We then incorporate literature values of visible measurements (in the form of the H absolute magnitude) to determine albedos. Using these data we investigate the albedo and diameter distributions of the Main Belt. As observed previously, we find a change in the average albedo when comparing the inner, middle, and outer portions of the Main Belt. We also confirm that the albedo distribution of each region is strongly bimodal. We observe groupings of objects with similar albedos in regions of the Main Belt associated with dynamical breakup families. Asteroid families typically show a characteristic albedo for all members, but there are notable exceptions to this. This paper is the first look at the Main Belt asteroids in the WISE data, and only represents the preliminary, observed raw size and albedo distributions for the populations considered. These distributions are subject to survey biases inherent to the NEOWISE dataset and cannot yet be interpreted as describing the true populations; the debiased size and albedo distributions will be the subject of the next paper in this series.

• The paper presents preliminary diameters and albedos for over 100,000 Main Belt asteroids using WISE/NEOWISE infrared data.
• It applies the NEATM thermal model, achieving diameter estimates with errors below 10% and uncovering a bimodal albedo distribution.
• The study highlights distinct compositional zones and collisional family trends, paving the way for future debiasing and refined solar system models.

A Comprehensive Study of Main Belt Asteroids with WISE/NEOWISE: Preliminary Albedos and Diameters

The paper "Main Belt Asteroids with WISE/NEOWISE I: Preliminary Albedos and Diameters" presents an extensive analysis of the physical characteristics of Main Belt asteroids (MBAs) using data from the WISE (Wide-field Infrared Survey Explorer) and its NEOWISE enhancement. The paper aims to compute preliminary diameters and albedos of over 100,000 MBAs by employing the NEATM (Near-Earth Asteroid Thermal Model) thermal model fitting routine, offering a substantial contribution to understanding the size and reflective properties of these celestial bodies.

Key Results and Methodology

1. Infrared Data Utilization: The paper harnesses the capabilities of WISE, a thermal infrared space telescope, to survey MBAs across four infrared wavelengths. The NEOWISE enhancement facilitated the targeted paper of Solar System objects. This approach allows for more accurate diameter estimates, reducing typical errors to less than 10%.
2. Diameter and Albedo Calculation: Diameters are derived from infrared (IR) flux observations using the NEATM model, which accounts for the beaming parameter—an indicator of surface thermal characteristics. Albedos are computed by integrating these IR measurements with visible light data (H absolute magnitude values).
3. Albedo and Diameter Distribution: The research identifies a bimodal albedo distribution across the Main Belt. The average albedo shows notable variations between the inner, middle, and outer regions of the Main Belt. This indicates diverse compositional characteristics across different zones of the Belt, which align with previous observations of asteroidal compositional gradients.
4. Dynamical Family Analysis: The paper observes that most asteroid families exhibit characteristic albedos, reinforcing the theory that these groups result from collisional fragmentation of a common progenitor. The investigation reveals instances of mixed-albedo families that might suggest complex collisional histories or potential interlopers in dynamically defined asteroid families.
5. Beaming Parameter Insights: With a substantial dataset, the paper finds a mean beaming parameter near 1.0, though it exhibits dependency on observational phase angle, which might influence future modeling approaches in thermal flux assessments.

Implications and Future Directions

The preliminary findings suggest that while these results provide a valuable snapshot of the MBA population, they are subject to inherent biases from the observational methodology. Future work is planned to undertake a comprehensive debiasing effort to refine the size and albedo distributions further. This refinement is critical for enhancing the accuracy of models related to the formation and evolutionary dynamics of the Main Belt.

Moreover, the paper's results regarding the albedo of the Baptistina family bring into question previous hypotheses linking it to the impactor responsible for the K/T extinction event, suggesting the need for recalibration of their historical models using accurate albedo data.

Concluding Remarks

This paper, leveraging the powerful WISE/NEOWISE dataset, offers a robust platform for expanding our understanding of asteroid characteristics on a massive scale, providing crucial constraints on theoretical models of solar system evolution. The ongoing and future analyses, particularly post-debiasing, are expected to yield finer insights into the collisional history and compositional diversity of the Main Belt, possibly influencing our broader understanding of planetary formation processes.