3 μm Spectroscopic Survey of Near-Earth Asteroids

Abstract

Near-Earth Asteroids (NEAs) are excellent laboratories for processes that affect airless body surfaces. S-complex (including V-type) NEAs were not expected to contain OH/H2O on their surfaces because they formed in the anhydrous regions of the solar system and their surface temperatures are high enough to remove these volatiles. However, a 3 μm feature typically indicative of OH/H2O was identified on other seemingly dry bodies in the inner solar system, raising the question of how widespread volatiles may be on NEAs. We observed 29 NEAs using both prism (0.7–2.52 μm) and LXD_short (1.67–4.2 μm) modes on SpeX on NASA’s IRTF in order to accurately characterize asteroid spectral type and the 3 μm region. Eight of the observed NEAs have a 3 μm absorption feature at >1σ (three of which are present to >2σ), and they exhibit four identified band shape types. Possible sources for OH/H2O on these bodies include carbonaceous chondrite impacts and/or interactions with protons implanted by solar wind. Characteristics such as composition and aphelion appear to play an important role in the delivery and/or retention of OH/H2O, as all eight NEAs with an absorption feature are S-complex asteroids and six enter the main asteroid belt. Additionally, perihelion, size, albedo, and orbital period may play a minor role. Our observations determined that nominally anhydrous, inner solar system bodies, and therefore near-Earth space in general, contain more OH/H2O than previously expected. The identified trends should help predict which NEAs that have not yet been observed might contain OH/H2O on their surfaces.

JWST Near-infrared Spectroscopy of the Lucy Jupiter Trojan Flyby Targets: Evidence for OH Absorption, Aliphatic Organics, and CO2

“…The spectra of all targets show significant contributions from thermal emission at wavelengths longer than ∼4 μm. We modeled and removed this thermal contribution using the Near Earth Asteroid Thermal Model (NEATM; Harris 1998), following the methods described in McGraw et al (2022). When implementing NEATM, we fixed the targets' sizes and albedos to literature values (see Table 2).…”

Evaluating possible spectroscopic variation of Bennu’s sampling site

“…MNRAS 519, 1464-1475 (2023) temperature caused decreased long wavelength reliability inducing few per cent uncertainty, as a result, this makes quantitatively estimations of variation percentage at Nightingale very difficult. Moreo v er, OH implantation could be responsible for variations across the surface as observed in other planetary bodies (McGraw et al 2019 ;Tang et al 2021 ). Ho we ver, the greater intensity of variation on Nightingale may be indicative of real surface variation o v er the noise and instrumental effects, although, given the observational caveats discussed before, it becomes difficult to e v aluate the real magnitude of these differences.…”

OSIRIS-APEX: An OSIRIS-REx Extended Mission to Asteroid Apophis

“…The broad spectral range covered by OVIRS and OTES (0.4-100 μm) may elucidate chemistry and mineralogy that were unanticipated by earlier missions to S-complex asteroids -in particular, the 3 μm feature indicative of hydration recently discovered in unresolved spacecraft and ground-based data of the stony asteroids Gaspra and Eros (Granahan 2013;Rivkin et al 2018;McGraw et al 2020). Because anhydrous minerals dominate stony asteroids, hydrogen implantation via solar wind is the leading theory for these observations.…”