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Differences in NEA Simple Thermal Model Results Between IRTF SpeX and NEOWISE Data

Presentation #506.07 in the session Asteroids: Near-Earth Objects (Oral Presentation)

Published onOct 23, 2023
Differences in NEA Simple Thermal Model Results Between IRTF SpeX and NEOWISE Data

Understanding the properties of Near-Earth Asteroids (NEAs) is critical for many aspects of space science, including investigating solar system formation and evolution, understanding the delivery of volatiles to Earth, and preparing for potential asteroid impacts. Two of the most important properties for these investigations are an object’s size and composition, both of which can be informed by knowledge of an object’s albedo. Albedos are commonly inferred for NEAs by using simple thermal models, such as NEATM, to analyze visible and infrared NEA spectra. However, these models employ many simplifying assumptions about the asteroids that they are modeling, which can result in large uncertainties in many cases. For instance, recent studies have shown that there are inconsistencies between sizes derived with simple thermal models, and sizes derived from other methods such as radar or occultations. Although these discrepancies are often around the 50% level, the sizes can be inconsistent by factors of two or more, at which point it causes issues for our interpretation of the risk posed by an object.

As part of an ongoing project to investigate the limitations of simple thermal models, we have found additional inconsistencies in NEA properties derived using these models. Modeling of multiple NEAs based on normalized flux spectra from the SpeX instrument on the NASA IRTF (in both reflected and thermal regions) and absolute photometry from NEOWISE has produced inconsistent albedo results. All data are analyzed using a simple thermal model we call our NEATM-like model. This model is based on the NEATM model but includes a rudimentary incorporation of thermal inertia. Overall, the model includes three free-floating parameters: visual geometric albedo, thermal inertia, and beaming parameter. The model is fit independently to both normalized flux data (SpeX) and absolute photometry data (NEOWISE). These fits often result in albedo estimates that can differ by up to a factor of two.

In this talk, we will present these discrepancies for a variety of different NEAs that represent a range of sizes, taxonomic types, and shapes. We will show how these discrepancies change based on these differing object properties and discuss the potential causes of them. Additionally, we will highlight how these discrepancies may affect our understanding of an NEA’s composition or size, and how this may influence our understanding of the overall NEA population.

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