DEEP UV RAMAN AND FLUORESCENCE SPECTROSCOPY WITH MORPHOLOGICAL ANALYSES OF NEOARCHEAN MICROBIALITES TO INFORM THE SEARCH FOR LIFE ON MARS

A primary science goal of NASA’s Mars 2020 mission is to search for evidence of ancient microbial life on Mars. To achieve this goal, the Perseverance rover is exploring Jezero Crater (3.2–3.8 Ga), which was once a delta-lake system. Jezero was chosen as the target for this mission because of the high likelihood that it was habitable during Mars’ Noachian period and because it is host to geological deposits with a high biosignature preservation potential. These include likely carbonate deposits at the paleolake margin near the inlet valley, just within the crater rim.

The rover’s science payload includes several cameras and instruments to facilitate the detection of evidence of past life that might be preserved in Jezero, such as organic matter, microbialites, or other biosignatures. One of these instruments is a deep ultraviolet (DUV) Raman and fluorescence spectrometer called SHERLOC (Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals). To allow for accurate interpretation of SHERLOC data, it is essential to build a library of Raman spectra collected from samples of Earth materials that are similar to the types of materials the Perseverance rover might encounter on Mars.

It is particularly important to include spectra collected from unambiguously biogenic terrestrial analog samples of carbonate microbialites for comparison to data collected from the carbonate deposits at the rim of Jezero Crater. To meet this need, we have scanned cuspate and plumose carbonate microbialites from the 2.5-billion-year-old (Neoarchean) Gamohaan Formation on the Kaapvaal Craton in South Africa using a SHERLOC analog DUV-Raman and fluorescence spectrometer. The analyzed samples are primarily composed of calcite and dolomite, some of which coprecipitated with the growing microbial structures, and contain abundant fossilized organic matter.

Here we will present the SHERLOC-analog Raman and fluorescence spectra alongside three-dimensional projections of the microbial morphology preserved within the Neoarchean microbialites, revealed through serial imaging and subsequent image projection, to demonstrate correlations between spectral and morphological features.