Hydration Features on Near-Earth Objects: Integrating New Data with Prior Results

TL;DR

This study investigates hydration features on near-Earth objects by integrating new spectral data with prior results, revealing that low-inclination and high-aphelion NEOs are more likely to exhibit surface water or hydroxyl features.

Contribution

The paper presents new 3-micron spectral observations of 15 NEOs and combines them with existing data to identify correlations between hydration features and orbital parameters.

Findings

Hydration bands found in 4 of 15 NEOs observed.

Band depth correlates with decreasing orbital inclination.

NEOs with low inclination and large aphelion are more likely to have surface water or hydroxyl.

Abstract

Near-Earth objects (NEOs) are excellent laboratories for testing processes that affect airless bodies, as well as informing us about Solar System history. Though most NEOs are nominally anhydrous because they formed inside the Solar System frost line and their surface temperatures are high enough to remove volatiles, a 3-micron feature typically indicative of OH/H2O has been identified on several such bodies. Possible sources for OH/H2O on these bodies include carbonaceous chondrite impactors or interactions with protons implanted by solar wind. The MIT-Hawaii Near-Earth Object Spectroscopic Survey (MITHNEOS) began its 3-micron observation campaign of NEOs in 2022 and has obtained spectral data of 15 predominantly nominally anhydrous (i.e., mostly S-complex or V-type) targets using NASA's Infrared Telescope Facility's (IRTF) near-infrared spectrometer, SpeX. Spectra were collected using both prism (0.7-2.52 micron) and LXD_short (1.67-4.2 micron) modes to accurately characterize asteroid spectral type and the 3-micron region. Four of the 15 NEOs observed exhibit a 3-micron feature, exhibiting band shapes similar to those identified in a previous NEO survey (McGraw et al. 2022), which found a trend between hydration band presence and large aphelion (i.e., Q > 2.06 AU). Combining our new observations with the pre-existing database of NEO 2-4-micron data revealed that band depth increases with decreasing orbital inclination and that all NEOs with hydration bands have i < 27 degrees with most having i < 14 degrees. We find that NEOs with low inclination and large aphelia are the most likely bodies in near-Earth space to possess surficial OH/H2O.