Solar radiation is the primary energy source for surface planetary life, so that pigments are fundamental components of any surface-dwelling organism. They may therefore have evolved in some form on Mars as they did on Earth. Photosynthetic microbes are major primary producers on Earth, but are concurrently vulnerable to ultraviolet (UV) damage. Using non-intrusive laser Raman spectroscopy to recognize the component parts of biomolecules, we have shown not only the abundance of microbial photosynthetic and photoprotective pigments in situ, but also their spatial distribution within their microhabitat. This essential aspect of their screening or avoidance survival strategies is lost on extraction with solvents. This precise approach is eminently suited to analysis of epilithic (surface) and endolithic (within rocks) communities in Antarctic desert habitats, which are putative analogues of early Mars. Raman spectra for key biomolecules (e.g. the UV screen parietin and the antioxidant β-carotene in epilithic lichens) enable not only the detection of organics in light-stratified habitats, but also the characterization of unknown pigments. Typical biomarkers of astrobiological relevance in our Raman spectral database include scytonemin (a UV screen), chlorophyll (primary photosynthetic pigment), phycocyanin (accessory pigment for shade adaptation) and a hopanoid extracted from 2·5 Gya microbial stromatolite from Australia. This compound dates from the same time period when a wetter Mars could have had a potentially flourishing surface microbial community of its own. Analyses with a laboratory Raman instrument have been extended to a novel miniature Raman spectrometer, operating at the same optimal excitation wavelength (1064 nm) via an In-Ga-As detector. After evaluation in Antarctica, this instrument will be space-qualified for a proposed Mars rover mission to detect biomolecules in the near-surface sediment profile of palaeolakes, using experience with Antarctic biomarkers to interpret alien spectra of fundamental components, without the need for prior knowledge of the identity of the target compounds.

The Raman spectra of cyanobacterial species, Gloecapsa and Nostoc, in clear gypsum crystals from the Haughton Crater, Devon Island, Canadian High Arctic, site of a meteorite impact during the Miocene some 23 Mya, have been recorded using several visible and near-infrared excitation wavelengths. The best spectra were obtained using a green wavelength at 514.5 nm and a confocal microscope with an image footprint of about 2 µ in diameter and 2 µ theoretical depth. Raman biosignatures for beta-carotene and scytonemin were obtained for one type of colony and parietin and beta-carotene for another; chlorophyll was detected in both types of colony. The different combination of these radiation protectant biomolecules suggests that the two cyanobacterial colonies, namely Nostoc and Gloecapsa, are adopting different survival strategies in the system. Confocal spectroscopic probing of the gypsum crystals exhibited sufficient discrimination for the identification of the biomolecules through the gypsum crystal, in simulation of the detection of extant or extinct halotrophs. This supports the viability of Raman spectroscopic techniques for incorporation as part of the instrumentation suite of a robotic lander for planetary surface exploration for the detection of organisms inside sulfate crystals from previous hydrothermal activity on Mars.