- The paper confirms water/hydroxyl detection via a 3 µm absorption feature with band depths between 2.72% and 3.26% on Psyche.
- Methodology involved dual-epoch observations using SpeX in LXD mode and precise thermal correction with NEATM.
- Findings indicate surface heterogeneity and suggest that collisional history introduced complex, hydrated materials on the metallic asteroid.
Detection of Water and/or Hydroxyl on Asteroid (16) Psyche
In this paper, the authors address the presence of hydration features on the M-type asteroid (16) Psyche, renowned for its substantial metallic composition. They employ the 3-µm spectral region analysis using LXD mode of the SpeX spectrograph/imager at the NASA IRTF. The choice of this wavelength is pivotal due to its sensitivity to water and hydroxyl group signatures, which signify hydroxyl or water-bearing phases on planetary bodies. The demonstration of these features on Psyche challenges previous perceptions of the asteroid as primarily metallic and suggests more complex surface compositions.
Methodological Approach
Psyche was observed on two occasions using the SpeX spectrograph in its long-wavelength, cross-dispersed mode, which spans 1.9-4.2 µm. The researchers implemented Spextool, an IDL-based reduction software, which facilitated the removal of atmospheric influences and extraction of precise spectral data. An essential step involved correcting for the thermal emission contribution using the Near-Earth Asteroid Thermal Model (NEATM). This correction is critical in isolating the 3-µm band attributed to hydration from thermal noise, ensuring the accuracy of their interpretations.
Key Findings
The spectral data confirmed the manifestation of a 3-µm absorption feature on (16) Psyche. The band depths calculated for various rotational phases ranged from approximately 2.72% to 3.26%, with uncertainties duly accounted for. These features bear resemblance to hydration patterns observed on other asteroid types and carbonaceous chondrite meteorites, suggesting the presence of phyllosilicates or other hydroxyl-bearing minerals.
The paper also recognized spectral variability tied to Psyche's rotation, hinting at surface heterogeneity in its metal/silicate ratio. This finding could signify hemispheric disparities or the inclusion of exotic materials from past collisions. The presence of other absorption features at certain rotational positions aligns with known impact structures, supporting the hypothesis of surface alteration by exogenic materials such as carbonaceous chondrites.
Implications and Future Directions
The discovery corroborates earlier hypotheses that larger M-type asteroids such as Psyche, with diameters exceeding 65 km, can exhibit hydrated minerals. This contradicts the metal core theory and aligns with the notion that such bodies have undergone significant collisional and transformational history. These insights pave the way for re-evaluating the surface processes and evolutionary history of metallic-dominated bodies in the asteroid belt.
The research opens avenues for future investigations utilizing space-borne observatories or possible missions to Psyche, like NASA's Psyche mission, which aims to provide further insight into its composition and structure. Such missions will potentially validate these ground-based findings and offer unprecedented clarity on Psyche's geology.
In conclusion, the paper advances our understanding of asteroid composition, specifically within those traditionally labeled as metallic. It prompts a reevaluation of characterizing these bodies, highlighting the intricate interplays of surface processes that have shaped them across the solar system's history.
