An Assessment of Organics Detection and Characterization on the Surface of Europa with Infrared Spectroscopy

TL;DR

This study evaluates Europa Clipper's potential to detect trace organic compounds on Europa's surface using near-infrared spectroscopy, demonstrating that even low-abundance organics can be identified with high confidence.

Contribution

The paper presents a simulation-based assessment of Europa Clipper's ability to detect trace organics in the 3-5 μm range, employing Bayesian analysis to improve detection thresholds.

Findings

Trace organic species at ~5% abundance are detectable at >3σ significance.

Bayesian model comparison lowers detection threshold to <1% abundance.

Multiple overlapping trace species can be simultaneously identified and quantified.

Abstract

Organics, if they do exist on Europa, may only be present in trace amounts on the surface. NASA's upcoming mission Europa Clipper is going to provide global, high quality data of the surface of Europa in the near-infrared (NIR), specifically the 3-5~$\mu$m region, where organics are rich in spectroscopic features. In this work we investigate Europa Clipper's ability to constrain the abundance of selected trace species of interest that span different chemical bonds found in organics, such as C-H, C=C, C$\equiv$C, C=O and C$\equiv$N, via NIR spectroscopy in the 3-5~$\mu$m wavelength region. We simulate reflectance spectra of these trace species mixed with water ice, at varying SNR and abundance fractions. The evidence for the trace species in a mixture is evaluated using two approaches: 1) calculating average strength of absorption feature(s), and 2) Bayesian model comparison (BMC) analysis. Our simulations show that sharp and strong spectroscopic features of trace ($\sim 5\%$ abundance by number) organic species should be detectable at $> 3\sigma$ significance in Europa Clipper quality data. A BMC analysis pushes the $3\sigma$ detection threshold of trace species even lower to $<1 \%$ abundance. We also consider an example with all trace species mixed together, with overlapping features, and BMC is able to retrieve strong evidence for all of them and also provide constraints on their abundance. These results are promising for Europa Clipper's capability to detect trace organic species, which would allow correlations to be drawn between the composition and geological regions with possibly endogenic material.