Benchmarking organic detection limits with OrganiCam, the prototype time-resolved fluorescence imager and Raman spectrometer for remote sensing from an Ocean World lander or from a Mars helicopter mission

Abstract:

Ocean worlds including Europa, Enceladus, and to a lesser extent Ceres are targets in the search for biomaterials beyond Earth because the existence of stable, long-lived oceans and sources of energy imply a habitable environment. Characterization of the icy surfaces is an important first step in the exploration of the content of the oceans contained below. Reservoirs of organic materials and possible biomaterials on Mars are likely to reside underground, where they are protected from radiation and thermal extremes. We have built a prototype “OrganiCam” imager and spectrometer that uses time-resolved laser stimulation and gated detection to distinguish organic fluorescence and Raman signatures from mineral luminescence. Organic and especially biomolecules tend to exhibit brief fluorescence that can be distinguished from mineral luminescence by its short lifetimes on the order of a few nano seconds. Thus, time-resolved fluorescence and Raman spectroscopies can uniquely identify organic molecules. This technique is being deployed in the Mars 2020 / SuperCam instrument in point mode. For imaging mode, OrganiCam’s laser beam is diffused over the imaged region (> 600 cm² at 2 m distance). OrganiCam contains a spectrometer for passive visible-range, active fluorescence and Raman spectra. For the latter, the laser beam diffuser is removed, providing sufficient stimulation for detection of the weaker Raman organic signatures at somewhat higher detection limits. The OrganiCam prototype instrument is assembled and will be tested for detection limits on organic materials including isolated nucleic acids and bacteria cells. We have performed preliminary experiments with micro-Raman spectroscopy to detect the signatures of isolated bacterial DNA. This work is of high relevance to understand training data collection needs for Organicam.