Constraining the Spectral Homogeneity of Near-Earth Asteroids

The visible and near-infrared spectral region has a wealth of information about the composition of near-Earth asteroids (NEAs), which has been captured in several taxonomic systems in distinct ways [1,2,3]. The subtle spectral variation of the few asteroids studied by spacecraft, (e.g. Eros, Vesta and Bennu), suggests that the global mixing of regolith materials at 10- to 100-meter scales is fairly complete. The spectral consistency of asteroid families, resulting from collisional disruption of larger bodies in the main asteroid belt, also confirms this uniformity in many, if not most, cases. However, on cm-scales in meteorites we often do see dramatic changes of materials and mixing of different components. NEAs can serve as a middle ground to put further constraints on how and where this mixing takes place, and over what spatial scales it is important.

We have NASA IRTF SpeX observations [4] of over 100 NEAs on multiple days separated by weeks to a month at a variety of viewing geometries. We have multiple apparitions for many, as a consistency check. We will compare the 0.8-2.5 micron reflectance spectra of NEAs of a variety of taxonomic classes, to determine how the variation across the surface compares to the repeatability of multiple observations. The repeatability of these observations is 4.5% including various systematic effects [5,6]. We compare this to the consistency of a single object measured multiple times per night, and over days. We can quantify the degree to which the spectral appearance is affected by phase reddening, and by rotation phase, when the period is well known. Our dataset is well-suited for an investigation of the range of spectral homogeneity in light of the expected uncertainties to better interpret the composition of NEAs and their role as potential space resources.

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[2] DeMeo F.E., et al., (2009) Icarus, 202, 160.

[3] Gaffey, M.J., et al., (1993) Icarus, 106, 573.

[6] Rayner, J. T., et al., (2003) PASP, 115, 362.

[5] Marsset, M., et al., (2020) ApJ Supp, 247, 73.

[6] Lewin, C.D., et al., (2020) AJ, 160, 130.