Analysis of Two-Band WISE Observations of Asteroids

The Wide Field Infrared Survey Explorer (WISE) is a space-based telescope that conducted a full-sky survey in the infrared in four wavelength bands centered at 3.4, 4.6, 12, and 22 μm (called W1, W2, W3, and W4, respectively), yielding observations of over 100,000 asteroids (Wright et al. 2010). The analysis of these observations was pioneered by the NEOWISE team (Mainzer et al. 2011). A curated subset of these observations was reanalyzed by Myhrvold et al. (2022), who used a reparameterization of the NEATM (Harris 1998) to eliminate unnecessary degrees of freedom within the model, avoid the assumption of constant emissivities, and obtain more accurate values of asteroid diameters, temperatures, and albedos. To date there has been no direct comparison of modeling accuracy of four-band and two-band results. In this work, we compared the results of the reparametrized NEATM for a curated set of 4,545 clusters of observations, representing 4,281 asteroids, observed with WISE in two wavelength bands (W2 and W3) to previous results from all four wavelength bands (W1, W2, W3, and W4) calculated by Myhrvold et al. (2022). This comparison was done with the goal of elucidating unique aspects of modeling with two infrared bands instead of four so that any potential biases or shortcomings could be anticipated for the upcoming surveys observing in two bands similar to W2 and W3, such as NEO Surveyor. The two-band fits usually yielded slightly smaller diameters than the four-band fits, with a median diameter difference of -10% with a 95% confidence interval of -2% to -32%. We obtained estimates of parameter uncertainties via bootstrap analysis. The median diameter uncertainty was 19% larger for the two-band fits than for the four-band fits. Comparing two-band diameters to a set of 24 high quality occultation derived diameters, the median error was -15% (95% confidence interval 12% to -40%). Compared to 2,772 NEOWISE four-band diameters for the same asteroids, the error was -8% (95% confidence interval 10% to -22%).

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Nathan Myhrvold, Pavlo Pinchuk, and Jean-Luc Margot. Analysis of Four-band WISE Observations of Asteroids. Planetary Science Journal, 3(2):30, 2022. https://doi.org/10.3847/PSJ/ac3232.

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