Laboratory characterization of hydrothermally processed oligopeptides in ice grains emitted by Enceladus and Europa

Abstract

The Cassini mission provided evidence for a global subsurface ocean and ongoing hydrothermal activity on Enceladus, based on results from Cassini’s mass spectrometers. Laboratory simulations of hydrothermal conditions on icy moons are needed to further constrain the composition of ejected ice grains containing hydrothermally altered organic material. Here, we present results from our newly established facility to simulate the processing of ocean material within the temperature range 80–150°C and the pressure range 80–130 bar, representing conditions suggested for the water–rock interface on Enceladus. With this new facility, we investigate the hydrothermal processing of triglycine (GGG) peptide and, for the first time, analyse the extracted samples using laser-induced liquid beam ion desorption (LILBID) mass spectrometry, a laboratory analogue for impact ionization mass spectrometry of ice grains in space. We outline an approach to elucidate hydrothermally processed GGG in ice grains ejected from icy moons based on characteristic differences between GGG anion and cation mass spectra. These differences are linked to hydrothermal processing and thus provide a fingerprint of hydrothermal activity on extraterrestrial bodies. These results will serve as important guidelines for biosignatures potentially obtained by a future Enceladus mission and the SUrface Dust Analyzer (SUDA) instrument onboard Europa Clipper. This article is part of the theme issue ‘Dust in the Solar System and beyond’.

Exploring the universe through dusty visions

“…Thus far, the instrument has accelerated positively and negatively charged ice particles containing aqueous solutions of sodium chloride below 0.2 M. The study also demonstrates the capability of SELINA to record time-of-flight mass spectra of 120 nm particles accelerated up to hypervelocities of 3000 m s −1 . The final paper in this collection by Khawaja et al [25] is dedicated to the detection of potential biosignature compounds in the icy dust particles emerging from the subsurface ocean of Saturn's moon Enceladus. In this work, triglycine peptide was hydrothermally processed at approximately 80 bar and 80°C to simulate conditions at the ocean-core boundary of Enceladus.…”