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

Organics, if they do exist on Europa, may only be present in trace amounts on the surface. NASA’s10 upcoming mission Europa Clipper is going to provide global, high quality data of the surface of Europa11 in the near-infrared (NIR), specifically the 3-5 µm region, where organics are rich in spectroscopic12 features. In this work we investigate Europa Clipper’s ability to constrain the abundance of selected13 trace species of interest that span different chemical bonds found in organics, such as C-H, C=C, C≡C,14 C=O and C≡N, via NIR spectroscopy in the 3-5 µm wavelength region. We simulate reflectance spectra15 of these trace species mixed with water ice, at varying SNR and abundance fractions. The evidence16 for the trace species in a mixture is evaluated using two approaches: 1) calculating average strength17 of absorption feature(s), and 2) Bayesian model comparison (BMC) analysis. Our simulations show18 that sharp and strong spectroscopic features of trace (∼ 5% abundance by number) organic species19 should be detectable at > 3σ significance in Europa Clipper quality data. A BMC analysis pushes the20 3σ detection threshold of trace species even lower to < 1% abundance. We also consider an example21 with all trace species mixed together, with overlapping features, and BMC is able to retrieve strong22 evidence for all of them and also provide constraints on their abundance. These results are promising23 for Europa Clipper’s capability to detect trace organic species, which would allow correlations to be24 drawn between the composition and geological regions with possibly endogenic material.