Abstract
Carotenoids are promising targets in our quest to search for life on Mars due to their biogenic origin and easy detection by Raman spectroscopy, especially with a 532 nm excitation thanks to resonance effects. Ionizing radiations reaching the surface and subsurface of Mars are however detrimental for the long-term preservation of biomolecules. We show here that desiccation can protect carotenoid Raman signatures in the desert cyanobacterium Chroococcidiopsis sp. CCMEE 029 even after high-dose gamma irradiation. Indeed, while the height of the carotenoids Raman peaks was considerably reduced in hydrated cells exposed to gamma irradiation, it remained stable in dried cells irradiated with the highest tested dose of 113 kGy of gamma rays, losing only 15–20% of its non-irradiated intensity. Interestingly, even though the carotenoid Raman signal of hydrated cells lost 90% of its non-irradiated intensity, it was still detectable after exposure to 113 kGy of gamma rays. These results add insights into the preservation potential and detectability limit of carotenoid-like molecules on Mars over a prolonged period of time and are crucial in supporting future missions carrying Raman spectrometers to Mars’ surface.
Highlights
The surface of Mars is a hostile environment for the preservation of signatures of past life due to the presence of oxidizing species, mainly perchlorates [1], and ionizing radiation [2] that can degrade organic molecules directly or through secondary oxidants [3]
We investigated by confocal Raman spectroscopy the permanence of the carotenoid signal in a desert strain of Chroococcidiopsis in two experimental conditions: one-year of air-dried storage, and exposure of hydrated and dried cells to increasing doses of γ-rays up to 113.25 kGy
The cyanobacterial strain was grown in BG11 medium by using 50-mL vented flasks, inside an incubator at 25 ◦ C, without shaking, under a photon flux density of 40 μmol m−2 s−1 provided by cool-white fluorescent lamp (4100 K) with a 16 h/8 h light/dark cycle
Summary
The surface of Mars is a hostile environment for the preservation of signatures of past life due to the presence of oxidizing species, mainly perchlorates [1], and ionizing radiation [2] that can degrade organic molecules directly or through secondary oxidants [3]. The detection of nucleic acids or peptides, with lengths in the range of tenths of monomers, is considered difficult to be refuted as a successful life detection [5]. Pigments, being the product of specific biochemical pathways, are considered unambiguously of biogenic origin, and, among. Carotenoids have been included in a high priority target list for biomolecule detection on Mars [8]. These molecules are generally easy to detect by Raman spectroscopy, and this a relevant feature since ESA/Roscomos’ ExoMars Rosalind Franklin rover and NASA’s Perseverance rover will carry Raman spectrometers, among other instruments, to detect signatures of life on Mars [9,10,11]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
