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Estimate of water and hydroxyl abundance on asteroid (16) Psyche from JWST data (2407.12162v1)

Published 16 Jul 2024 in astro-ph.EP

Abstract: Our understanding of Solar System evolution is closely tied to interpretations of asteroid composition, particularly the M-class asteroids. These asteroids were initially thought to be the exposed cores of differentiated planetesimals, a hypothesis based on their spectral similarity to iron meteorites. However, recent astronomical observations have revealed hydration on their surface through the detection of 3-$\mu$m absorption features associated with OH and potentially H2O. We present evidence of hydration due mainly to OH on asteroid (16) Psyche, the largest M-class asteroid, using data from the James Webb Space Telescope (JWST) spanning 1.1 - 6.63 $\mu$m. Our observations include two detections of the full 3-$\mu$m feature associated with OH and H2O resembling those found in CY-, CH-, and CB-type carbonaceous chondrites, and no 6-$\mu$m feature uniquely associated with H2O across two observations. We observe 3-$\mu$m depths of between 4.3 and 6% across two observations, values consistent with hydrogen abundance estimates on other airless bodies of 250 - 400 ppm. We place an upper limit of 39 ppm on the water abundance from the standard deviation around the 6-$\mu$m feature region. The presence of hydrated minerals suggests a complex history for Psyche. Exogenous sources of OH-bearing minerals could come from hydrated impactors. Endogenous OH-bearing minerals would indicate a composition more similar to E-or P-class asteroids. If the hydration is endogenous, it supports the theory that Psyche originated beyond the snow line and later migrated to the outer main belt.

Citations (1)

Summary

  • The paper estimates water and hydroxyl abundance on asteroid (16) Psyche using JWST data, detecting 3-μm absorption features indicating OH but placing an upper limit of 39 ppm on water content.
  • Observations reveal Psyche's composition includes hydrated minerals and metal-rich materials consistent with carbonaceous chondrites, suggesting a more complex history possibly involving formation beyond the snow line or influx of hydrated impactors.
  • These findings underscore the importance of advanced spectral analysis for understanding minor planet composition and volatile distribution, highlighting JWST's capability to refine models of asteroid differentiation and solar system evolution.

Insights into the Composition of Asteroid (16) Psyche from JWST Observations

The paper presented by Jarmak et al. focuses on estimating water and hydroxyl abundance on asteroid (16) Psyche using data obtained from the James Webb Space Telescope (JWST). These findings offer significant insights into both the asteroid's composition and broader implications for solar system evolution models. The observations span wavelengths from 1.1 to 6.63 μm, providing a new perspective on Psyche, which has traditionally been classified as an M-class asteroid, potentially the remnant metal core of a differentiated planetesimal.

Key Observations and Results

The data acquired from JWST indicated the presence of hydration on Psyche, primarily due to OH features. Two significant detections of the 3-μm absorption band, attributed to OH and potentially H2_2O, were observed with depths ranging from 4.3% to 6% across different segments. This observation aligns with hydrogen abundance estimates found in other airless bodies within the solar system. However, a 6-μm feature, which would clearly signal the presence of H2_2O, was not detected, allowing the researchers to place an upper limit on the water content of 39 parts per million.

Beyond hydration, the reflectance spectrum exhibited features consistent with those found in certain carbonaceous chondrites, similar to CY, CH, and CB types, indicating a composition that might include hydrated minerals and metal-rich materials. These results suggest a more complex history for Psyche than previously hypothesized.

Implications for Psyche’s Origin and Solar System Dynamics

The presence of OH-bearing minerals on Psyche suggests two potential scenarios: the influx of hydrated impactors or an endogenous origin with hydration as an intrinsic characteristic of the asteroid. The latter would imply Psyche may have originated beyond the snow line, a zone in the solar nebula where icy compounds could condense, and later migrated to its current location in the outer main belt. This hypothesis could point to a dynamic history where Psyche, or similar bodies, contributed to the delivery of volatiles to inner solar system bodies, potentially affecting early Earth conditions.

The absence of a distinct water feature at the 6-μm mark suggests that any present hydration is more likely to be attributed to OH than molecular water. This differentiation is critical for understanding Psyche's surface processes and potential space weathering effects that could influence the retention of water or hydroxyl groups.

Future Research Directions

The current paper sets the stage for further inquiries once the Psyche mission reaches the asteroid. Targeted investigations by the Psyche spacecraft, including high-resolution imaging and in situ measurements of elemental compositions, will complement these remote observations, potentially refining models of asteroid differentiation and volatile content.

Moreover, the results emphasize the importance of advanced spectral analysis for deciphering complex astronomical surfaces. The methodologies developed here could be applied to other celestial bodies within the asteroid belt, leading to broader applications in understanding the distribution and evolution of water and hydroxyls in the solar system.

While the data provide robust initial insights, the paper highlights the need for continued spectroscopic development, especially the need for differentiation between hydroxyl and water features at the atomic level. As the first comprehensive paper using JWST data on Psyche, this work underscores the telescope's utility in shifting paradigms about minor planets and their role in solar system development.

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