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Case Study for 3-µm Band Depth Variations: (433) Eros, (1036) Ganymed, & (3122) Florence

Presentation #506.08D in the session Asteroids: Near-Earth Objects (Oral Presentation)

Published onOct 23, 2023
Case Study for 3-µm Band Depth Variations: (433) Eros, (1036) Ganymed, & (3122) Florence

Near-Earth Asteroids (NEAs) are excellent laboratories for processes that affect the surfaces of airless bodies. Prior to the discovery of OH/H2O on the Moon (e.g., Sunshine et al. 2009), nominally anhydrous NEAs were not expected to contain OH/H2O on their surfaces because they formed within the frost line of the Solar System and their surface temperatures are high enough to remove these volatiles. 3-µm features typically indicative of OH/H2O have since been identified on additional seemingly dry bodies in the inner Solar System, such as Vesta (e.g., De Sanctis et al. 2012) and several S-complex NEAs, including (433) Eros, (1036) Ganymed, and (3122) Florence (e.g., McGraw et al. 2022). Possible sources for OH/H2O on these bodies include carbonaceous chondrite impacts or interactions with protons implanted by solar wind. We investigated the causes of band depth and shape variations on NEAs by comparing new observations of Eros and Ganymed to those previously published (e.g., Rivkin et al. 2018) and conducting a rotationally-resolved spectral study on Florence.

We observed all three asteroids using SpeX on NASA’s IRTF. Spectra were collected using both prism (0.7-2.52 µm) and LXD_short (1.67-4.2 µm) modes in order to accurately characterize asteroid spectral type and the 3-µm region. We analyzed 16 spectra of Eros, 13 spectra of Ganymed, and four rotationally-resolved spectra of Florence to study potential band depth and shape variations. The four spectra of Florence were created from one observation of Florence that covered almost two complete rotations.

Various characteristics, including sub-solar latitude, heliocentric distance, and observing parameters, were investigated to determine the cause of the band depth variance for these three NEAs. All three asteroids possess exogenously sourced OH/H2O and have spectra that show potential spatial correlations in band depth or shape. Understanding the factors controlling these varying band depths will enable further understanding of the processes by which OH/H2O is delivered and/or retained on NEA surfaces.

De Sanctis et al. 2012. Detection of widespread hydrated materials on Vesta by the VIR imaging spectrometer on board the dawn mission. ApJ Letters 758, 5.

McGraw et al. 2022. 3 µm Spectroscopic Survey of near-Earth Asteroids. The Planetary Science Journal, vol. 3, no. 10, p. 243.

Rivkin et al. 2018. Evidence for OH or H2O on the surface of 433 Eros and 1036 Ganymed. Icarus 304, 74-82.

Sunshine et al. 2009. Temporal and Spatial Variability of Lunar Hydration as Observed by the Deep Impact Spacecraft. Science 326, 565-568.

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