The persistence of a chlorophyll spectral biosignature from Martian evaporite and spring analogues under Mars-like conditions

Abstract

Spring and evaporite deposits are considered two of the most promising environments for past habitability on Mars and preservation of biosignatures. Manitoba, Canada hosts the East German Creek (EGC) hypersaline spring complex, and the post impact evaporite gypsum beds of the Lake St. Martin (LSM) impact. The EGC complex has microbial mats, sediments, algae and biofabrics, while endolithic communities are ubiquitous in the LSM gypsum beds. These communities are spectrally detectable based largely on the presence of a chlorophyll absorption band at 670 nm; however, the robustness of this feature under Martian surface conditions was unclear. Biological and biology-bearing samples from EGC and LSM were exposed to conditions similar to the surface of present day Mars (high UV flux, 100 mbar, anoxic, CO 2 rich) for up to 44 days, and preservation of the 670 nm chlorophyll feature and chlorophyll red-edge was observed. A decrease in band depth of the 670 nm band ranging from *16 to 80% resulted, with correlations seen in the degree of preservation and the spatial proximity of samples to the spring mound and mineral shielding effects. The spectra were deconvolved to Mars Exploration Rover (MER) Pancam and Mars Science Laboratory (MSL) Mastcam science filter bandpasses to investigate the detectability of the 670 nm feature and to compare with common mineral features. The red-edge and 670 nm feature associated with chlorophyll can be distinguished from the spectra of minerals with features below *1000 nm, such as hematite and jarosite. However, distinguishing goethite from samples with the chlorophyll feature is more problematic, and quantitative interpretation using band depth data makes little distinction between iron oxyhydroxides and the 670 nm chlorophyll feature. The chlorophyll spectral feature is observable in both Pancam and Mastcam, and we propose that of the proposed EXOMARS Pancam filters, the PHYLL filter is best suited for its detection.

Protection of cyanobacterial carotenoids' Raman signatures by Martian mineral analogues after high‐dose gamma irradiation

“…But four to five layers of cyanobacterial cells mixed with Martian mineral analogues were sufficient to preserve both their fluorescence and Raman signals even after 383 Mars equivalent days of UV irradiation . And the chlorophyll infrared spectral signature was even shown to be preserved in two Martian evaporite analogues after irradiation with a ~300 Mars years equivalent UV flux …”

“…Among them are Raman, fluorescence, and infrared spectrometers. These rapid and non‐destructive techniques allow for both a better understanding of the mineralogy and geology of the landing site and samples and the identification of potential biosignatures within their mineralogical context . Raman spectrometers will be for the first time sent to another planet as part of the payloads of the next two Martian rovers: the Raman laser spectrometer, operating at a 532‐nm excitation wavelength, on the ExoMars2020 mission, and both a remote pulse‐gated at 532 nm (SuperCam) and an ultraviolet (UV) at 248.6 nm (SHERLOC) Raman spectrometers for the Mars2020 rover…”

Gypsum-hosted endolithic communities of the Lake St. Martin impact structure, Manitoba, Canada: spectroscopic detectability and implications for Mars

“…Each camera includes a small eight-position filter wheel to allow surface mineralogical studies in the 400-1100 nm wavelength region, with a number of filter band passes falling below 800 nm (Bell et al 2003). The possibility of detection of the spectral features due to biological pigments in gypsum-hosted endolithic communities using Pancam-type spectra is something that has yet to be investigated thoroughly, but preliminary results suggest that it is detectable in endolithic spectra, even after exposure to Mars surface conditions (Stromberg et al 2014). The prominent 670 nm endolith feature would have the greatest likelihood of being detected using the L3 filter, which has a central wavelength of 673 nm and a band pass of 16 nm (Bell et al 2003), perhaps appearing as a downward 'kink' relative to the bands on either side.…”

“…Subsequent changes in the terrestrial and Martian environment would have caused organisms to adopt various survival strategies, such as the colonization of new habitats and the adaptation of suitable protective mechanisms and strategies (Martinez-Frias et al 2006;Villar et al 2006;Edwards 2010). Chemical traces of these extinct microbial cells may have survived the Martian surface shielded within rocks (Stoker & Bullock 1997;Dartnell et al 2012;Dartnell and Patel 2013;de Vera et al 2013;Poch et al 2013;Stromberg et al 2014). Chemical traces of these extinct microbial cells may have survived the Martian surface shielded within rocks (Stoker & Bullock 1997;Dartnell et al 2012;Dartnell and Patel 2013;de Vera et al 2013;Poch et al 2013;Stromberg et al 2014).…”

Environmental conditions of E Iberia’s Early Triassic: an Earth example for understanding the habitability of ancient Mars

“…Considering the only known example of our planet, the concept is based not only on the existence in the system of carbon compounds and liquid water, but also on whether appropriate environmental conditions are available to support life, even if life does not currently exist (Javaux and Dehant, 2010). Further information about habitability and Mars can be found in Bishop et al (2004), Knoll and Grotzinger (2006), Martínez-Frías et al (2007), Gómez et al (2012), Bishop et al (2013), Jaumann et al (2013), Michalski et al (2013), Westall et al (2013), Bridges (2014), Bridges et al (2015), Cockell (2014), Léveillé et al (2014), Martínez-Frías (2014), Preston and Dartnell (2014), Stromberg et al (2014), Greenberger et al (2015), Grotzinger et al (2015), Rölin et al (2015) and Schwenzer et al (2016) among others.…”