Exploring Key Solar System Evolutionary Processes by Debiasing the Main Asteroid Belt

Collisions, gravitational forces, and non-gravitational forces like YORP and Yarkovsky drift are three major processes that shape planetary systems. Due to their small sizes and lack of atmospheric weathering, asteroids are the most well-preserved tracers of these forces. The Main belt between Mars and Jupiter is the most numerous asteroid population known and houses dozens of identified collisional families of varying ages and compositions, fossilizing evidence of these evolutionary processes at diverse time stamps and under different compositional contexts. Fundamental Main belt asteroid (MBA) properties like shape and size-frequency distribution (SFDs) are key constraints on solar system evolutionary models, yet these properties for the Main belt’s constituent subpopulations remain either unknown or inadequately constrained due to rampant biases in the surveys used to determine them.

We will model survey efficiencies, construct debiased SFDs, and constrain the shape and spin pole distributions for 21 prominent collisional families in the Main belt and for six dynamically distinct regions of non-family (i.e., background) MBAs. For this effort, we will leverage archived 12-micron asteroid photometry taken during the NEOWISE space mission’s cryogenic phase. These data are uniquely well suited for debiasing due to far fewer observational biases, a large sample size of ~130,000 asteroids with reliable MBA orbits, a regular survey cadence, and well understood and stable survey sensitivities. Toward building synthetic asteroid models with as much relevant accuracy as possible, we will also determine shape/elongation and pole latitude distributions for each subpopulation explored in the proposed work. We will use then use the NEOWISE data to determine detection efficiency functions across several parameters down to diameters (D) of ~3 km. We will then extend our NEOWISE-debiased SFDs down to D ~ 1 km by comparing them to the full MBA catalog and assessing underlying biases.

By comparing debiased SFDs of old versus young families of similar composition, we can ascertain how quickly and in what ways continuous evolutionary forces are reshaping small body populations. We can also help understand how impact physics differ between different types of material by comparing debiased SFDs and shape distributions of carbonaceous (C-type) families to more siliceous (S-type) families. The shape and spin pole distributions determined here will also be used to assess how quickly ongoing collisional grinding softens asteroid dimensions and how efficiently YORP realigns rotation axes. We will also improve the mass budget estimate of the Main belt using our debiased SFDs to better constrain dynamical and collisional depletion and accumulation models. The proposed work would capitalize on established methods and underutilized archived datasets to offer a treasure trove of constraints on solar system formation and evolution, thus delivering high overall scientific impact with very little risk.