The Spectroscopic Impact of Sublimation Under Martian Surface Conditions: Implications for Sample Analysis by the Rosalind Franklin Rover and Biosignature Preservation

Abstract The 2028 ESA/NASA Rosalind Franklin Mission (RFM) will search for signs of past and present life in the shallow subsurface of Mars. It is crucial to understand how minerals and any biosignatures uncovered during these sampling activities might change and be identified under today's Martian conditions. This preliminary study explored the effects of cryodesiccation, induced by the sub‐zero, near‐vacuum conditions on the Martian surface, on Ca‐sulfate, the SOPHIA Mars soil simulant and an Antarctic microbial mat collected during the Scott Expedition. Powdered samples were analyzed via Visible‐Near‐Infrared (Vis‐NIR) and Fourier Transform Infra‐Red spectroscopy to emulate future analyses by the PanCam and Enfys instruments and placed in a lyophilizer maintained at −63.4°C with a vacuum of 1.182 mbar for 1 hr and 72 hr. After 1 hr exposure, Mars‐like sublimation processes began within the three Mars analog samples, increasing the spectral intensity of the mineralogical, hydration, and organic features within the samples. After 72 hr exposure, sublimation reactions were ongoing, with hydration‐ and organic‐induced spectral bands observed to decrease in intensity and detectability, with some features now removed. Understanding how sampling activities and subsequent environmental exposure affect the mineralogical and organic content of samples, and how to spectrally identify these changes using rover instrumentation, is vital in assessing the reliability of the data uncovered, the differences between the subsurface and surface environments at Oxia Planum, and therefore the environmental and biological interpretations made.