Detecting extraterrestrial life with FTIR and Raman on space missions is not Sci-Fi, it’s an excellent chance to make first contact.
Space – the final frontier
Are we alone? That is a central question in many disciplines, from philosophy to astrobiology. Even though the methods used to address this vary significantly, a central question remains in all disciplines. What are we actually searching for?
Detecting extraterrestrial life
Our concept of extraterrestrial life is diverse and largely influenced by science fiction. But while we enjoy speculating about how the first contact with alien species might unfold, in reality, we need to tamper our warp speed a bit… at least for now.
Why? Because the aliens we’re most likely to encounter first aren’t little green men but tiny microorganisms, or more probably, their remains. Doesn’t sound too thrilling at first, does it? But the search for extraterrestrial microorganisms is far more challenging than learning the Vulcan salute 🖖.
It is, in fact, the proverbial search for a needle in a haystack. Microorganisms are extremely small and quickly deteriorate which makes their detection, especially on other planets, challenging. On planets like Mars, ionizing cosmic rays additionally accelerate their degradation. This raises the question: how can we determine if microorganisms ever inhabited a planet?
Biominerals – the more resilient „aliens“
The answer is to search for so called biominerals. Biominerals are mineral substances that are formed by living organisms through biologically mediated processes. These minerals can serve as structural support, defense mechanisms, or play an important role in the metabolic pathway of the organism.
On Mars, biotic iron reduction by hyperthermophilic microbes could have been such a metabolic pathway. These organisms thrive in hydrothermal systems and reduce Fe(III) to Fe(II) minerals such as magnetite or siderite. The dilemma at hand? Can these biominerals be clearly distinguished from their abiotically formed counterparts? And on top of that on planets that are light-years away from us?
The answer is yes! We may not have long-range sensors or tricorders available, but we have something similarly effective: FTIR and Raman spectroscopy!
Biogenic or abiogenic?
In a set of experiments researchers tested if it is possible to distinguish abiotically formed minerals from biominerals. For this they incubated the hyperthermophilic Fe(III)-reducing crenarchaea1, Pyrodictium delaneyi (P. del) and Pyrobaculum islandicum (P.isl) and let them bioreduce Ferrihydrite, Lepidocrocite and Akaganeit.
Additionally, they left the starting minerals in an uninocculated medium as an abiotic control. The material was then collected, dried and analyzed by FTIR-ATR spectroscopy and Raman microscopy using Bruker devices.
FTIR-ATR results
FTIR-ATR revealed differences in iron mineralogy between minerals formed by bioreduction and under abiotic conditions. Both P. delaneyi and P. islandicum produced magnetite upon bioreduction of ferrihydrite, displaying absorption peaks at 542 and 320 cm-1.
Both organisms exhibited broad absorption bands indicative of phosphate in the 900–1200 cm-1 region which might stem from the growth medium. In the 1200–1700 cm-1 region, bioreduced ferrihydrite by P. delaneyi showed a broadened feature.
This broadening potentially indicated contributions from carbonate, phosphate minerals, and cell-associated proteins. The abiotic samples both showed a strong resemblance to Ferrihydrite with only additional peaks in the 900–1200 cm-1 region indicative of medium-associated or mineral phosphates.
Lepidocrocite bioreduced by P. delaneyi showed evidence of siderite, with distinctive absorptions at 730, 860, and 1400 cm-1. P. islandicum presented minor differences between bioreduced and abiotic controls.
Raman results
Raman showed that changes in growth media and the heat treatment induced subtle mineral changes and band shifts towards lower wavenumbers for both ferrihydrite and lepidocrocite.
Ferrihydrite exhibited a major peak at ~710 cm-1, with high wavenumber features at 695 cm-1 and 735 cm-1. Bioreduced ferrihydrite by P. delaneyi showed band positions at 677 cm-1 and 721 cm-1, shifting towards magnetite. P. islandicum bioreduced ferrihydrite displayed a subtle shift towards lower wavenumbers.
The P. delaneyi unheated and heated abiotic controls for lepidocrocite showed bands shifted to lower wavenumbers, notably a feature at 1056 cm-1 shifting to 1073 cm-1. Bioreduced lepidocrocite also displayed shifts at 382 cm-1 and 1057 cm-1 towards lower wavenumbers.
Lepidocrocite bioreduced by P. delaneyi exhibited unique features at 294 cm-1 and 1084 cm-1, possibly indicating a ferrous carbonate phase.
Conclusion
Can biominerals serve as evidence of life on other planets? The study showed that FTIR and Raman can indeed be used to asses if minerals formed through bioreduction or abiotic processes. While more research on this has to be carried out in the future, biominerals might become silent storytellers of ancient life on other planets.
And who knows, maybe a future Astronaut will bring an ALPHA or SENTERRA along on future Missions. In any case, we at Bruker are eagerly anticipating the deployment of FTIR and Raman instruments on foreign worlds.
Do you want to know more about how Raman can be used in a geological context? Then visit our Blog about Geoscientific Raman applications
- Archaea are a group of single-celled microorganisms that are distinct from bacteria and often thrive in extreme environments. ↩︎
