Limits of life and the habitability of Mars: The ESA space experiment BIOMEX on the ISS

BIOMEX (BIOlogy and Mars EXperiment) is an ESA/Roscosmos space exposure experiment housed within the exposure facility EXPOSE-R2 outside the Zvezda module on the International Space Station (ISS). The design of the multiuser facility supports—among others—the BIOMEX investigations into the stability and level of degradation of space-exposed biosignatures such as pigments, secondary metabolites, and cell surfaces in contact with a terrestrial and Mars analog mineral environment. In parallel, analysis on the viability of the investigated organisms has provided relevant data for evaluation of the habitability of Mars, for the limits of life, and for the likelihood of an interplanetary transfer of life (theory of lithopanspermia). In this project, lichens, archaea, bacteria, cyanobacteria, snow/permafrost algae, meristematic black fungi, and bryophytes from alpine and polar habitats were embedded, grown, and cultured on a mixture of martian and lunar regolith analogs or other terrestrial minerals. The organisms and regolith analogs and terrestrial mineral mixtures were then exposed to space and to simulated Mars-like conditions by way of the EXPOSE-R2 facility. In this special issue, we present the first set of data obtained in reference to our investigation into the habitability of Mars and limits of life. This project was initiated and implemented by the BIOMEX group, an international and interdisciplinary consortium of 30 institutes in 12 countries on 3 continents. Preflight tests for sample selection, results from ground-based simulation experiments, and the space experiments themselves are presented and include a complete overview of the scientific processes required for this space experiment and postflight analysis. The presented BIOMEX concept could be scaled up to future exposure experiments on the Moon and will serve as a pretest in low Earth orbit

Linking remote sensing, in situ and laboratory spectroscopy for a Ryugu analog meteorite sample

In 2022 JAXA issued an Announcement of Opportunity (AO) for receiving Hayabusa2 samples returned to Earth. We responded to the AO submitting a proposal based on using a multi-prong approach to achieve two main goals. The first goal is to address the subdued contrast of remote-sensing observations compared to measurements performed under laboratory conditions on analog materials. For this we will link the hyperspectral and imaging data collected from the spacecraft and the in-situ observations from the MASCOT lander instruments (MARA and MASCam) with laboratory-based measurements of Hayabusa2 samples using bi-directional reflectance spectroscopy under simulated asteroid surface conditions from UV to MIR/FIR achieved using three Bruker Vertex 80 V spectrometers in the Planetary Spectroscopy Laboratory. The second goal is the investigation of the mineralogy and organic matter of the samples collected by Hayabusa2, to better understanding the evolution of materials characterizing Ryugu and in general of protoplanetary disk and organic matter, investigating the aqueous alteration that took place in the parent body, and comparing the results with data collected from pristine carbonaceous chondrite analog meteorites. Spectral data will be complemented by Raman spectroscopy under simulated asteroid surface conditions, X-ray diffraction, would also allow us to define the bulk mineralogy of the samples as well as investigate the presence and nature of organic matter within the samples. In situ mineralogical and geochemical characterization will involve a pre-characterization of the sample fragments through scanning electron microscopy low voltage electron dispersive X-ray (EDX) maps, and micro IR analyses of the fragments. If allowed, a thin section of one grain will be used for electron microprobe analyses to geochemically characterize its mineralogical composition. To train our data collection and analysis methods on a realistic sample, we selected a piece of the Mukundpura meteorite, as one of the closer analogs to Ryugu’s surface (Ray et al., Planetary and Space Science, 2018, 151, 149–154). The Mukundpura chunk we selected for this study measures 3 mm in its maximum dimension, and we chose it so to have a test sample of the same size as the Hayabusa2 grain we requested in our proposal to JAXA’s AO. The test gave us confidence that we can measure with good SNR measurements in bi-directional reflectance for samples around 3 mm in size (see Figures 3, 4 below). To address our second goal the spectral data was complemented by Raman spectroscopy measured again under simulated asteroid surface conditions in our Raman Mineralogy and Biodetection Laboratory at DLR

Preservation of carotenoids in salts and Mars regolith in various conditions

The search for life on Mars requires new tools and techniques. Among them, Raman spectroscopy is a powerful and non-destructive method for detecting biosignatures during missions to Mars such as NASA’s Perseverance and ESA/ROSCOSMOS’s Rosalind Franklin rovers. It is therefore important to study the detection possibilities of model biosignatures and their preservation in various conditions over time in order to guide future missions and interpret future data. Cyanobacterial photoprotective pigments (namely carotenoids) have been extensively used as suited targets for such measurements and to serve as biosignature models thanks to their stability and easy identification by Raman spectroscopy. Carotenoid decomposition can be caused by oxidation1 (prevented by higher humidity) and irradiation (prevented by lower humidity2). Carotenoids seem to be decomposing at different rates in different sets of conditions and on different matrices. During the preparation phase of BioSigN (BioSignatures and habitable Niches) we explore the possibility that different matrices enhance or diminish preservation of detectable carotenoid signal under different storage conditions. Both pure molecular β-carotene and cyanobacterium Nostoc sp. (strain CCCryo 231-06) were used

A MISSION CONCEPT FOR LAVA TUBE EXPLORATION ON MARS AND MOON –THE DLR SCOUT ROVER

The goal of the mission is to enter a martian or lunar skylight in order to check for cave continuations and placement of a sensor suite. A camera will also be used in order to deliver visible light images for context. With a combination of the navigation suite and communication modules, the cave passages will also be surveyed in order to produce a map, as is tradition in terrestrial speleology.From a technical point of view, themission is planned to be as simple as possible. Thus,it is planned to discard rope access systems and tofocus on sufficient robustness of the rover system. This allows for dropping into smaller skylights (10-20m depth) or larger ones, partially filled with regolith.Figure 1illustrates an overview of the mission sequencewhich is designed to be“one way”, i.e. the rover is going into the cave but never out again. Itallows to take a higher risk of going beyond obstaclesthat are not reversible and to omit the need for a recharging system for the rover once it is in the cave. Thus,the mission inside the cave will last as long as the battery runtime. As the scout rover is a small, lightweight system, several such roversmay be part of one mission to increase the exploration impact and science return.In order to access an entrance of a lava tube there are several options to be considered: having a bigger main rover that is delivering one or more Scoutsfrom the landing moduleto the entrance, or havingthe Scout equipped with solar panels to make the approach on its own. The first option isfavorable as system complexity of the Scout is reduced, while the second option ispreferred for rough terrain during the approach

Bridging the gap - linking remote sensing, in-situ and laboratory spectroscopy

Sample return provides us with “ground truth” about the visited body, verifying and validating conclusions that can be drawn by remote sensing (both Earth-based and by spacecraft) and via landed instruments on other bodies. The detailed investigation of the mineralogy and geochemistry of Ryugu plays a fundamental role in the understanding of its formation processes, and thereby gather further knowledge about the building blocks of the solar system. Based on the preliminary data from remote sensing measurements and laboratory-based measurements, Ryugu is rich in hydrated carbonaceous chondrite (CC) like material and more specifically it is very similar to Ivuna-like (CI) carbonaceous chondrites [1]. These meteorites are characterized by a high abundance of phyllosilicates and organic matter [2], which makes them have a low albedo. However, Ryugu seems to be even darker than CIs, as well as being more porous and fragile [1]. Back in August 2022, the Institute of Planetary Research at DLR (Berlin) received a fragment retrieved by the Hayabusa2 mission from asteroid Ryugu. The fragment assigned to us for analyses is sample A0112, from chamber A. Our investigation is based on two main goals. The first goal is to address a fundamental challenge in the interpretation of remote sensing data which was seen during the initial analysis of the Hayabusa 2 samples. Observations of planetary surfaces using spectroscopy have shown subdued contrast compared to measurements performed under laboratory conditions on analog materials. A strong focus of the work performed at PSL over the last decade has been to understand - and if possible minimize – the difference between laboratory and remote sensing observations (e.g. [3, 4, 5, 6]). Simulating the conditions on the target body as well as accurately reproducing the observing geometries have gone a long way towards that goal, however differences remain. A suggested explanation is the difference between terrestrial analog materials including even meteorites and the surfaces of planetary bodies. With Ryugu samples this hypothesis can be tested further, leading to a deeper understanding of the link between laboratory and remote sensing observations and thus benefiting not only the analysis of Hayabusa 2 data but of all remote sensing observations of planetary surfaces using spectroscopy. The second goal building on this is an investigation of the mineralogy and organic matter of the samples collected by Hayabusa 2, to better: a) understand the evolution of the materials characterizing asteroid Ryugu and therefore advance our knowledge of the mineralogy of the protoplanetary disk and organic matter (OM); b) investigate the aqueous alteration that took place in the parent body that lead to its current chemical and mineralogical characteristics; c) compare the results with data collected from pristine carbonaceous chondrite meteorites rich in hydrated minerals and organic matter

Carotenoid Raman Signatures Are Better Preserved in Dried Cells of the Desert Cyanobacterium Chroococcidiopsis than in Hydrated Counterparts after High-Dose Gamma Irradiation

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

Is There Such a Thing as a Biosignature?

The concept of a biosignature is widely used in astrobiology to suggest a link between some observation and a biological cause, given some context. The term itself has been defined and used in several ways in different parts of the scientific community involved in the search for past or present life on Earth and beyond. With the ongoing acceleration in the search for life in distant time and/or deep space, there is a need for clarity and accuracy in the formulation and reporting of claims. Here, we critically review the biosignature concept(s) and the associated nomenclature in light of several problems and ambiguities emphasized by recent works. One worry is that these terms and concepts may imply greater certainty than is usually justified by a rational interpretation of the data. A related worry is that terms such as “biosignature” may be inherently misleading, for example, because the divide between life and non-life—and their observable effects—is fuzzy. Another worry is that different parts of the multidisciplinary community may use non-equivalent or conflicting definitions and conceptions, leading to avoidable confusion. This review leads us to identify a number of pitfalls and to suggest how they can be circumvented. In general, we conclude that astrobiologists should exercise particular caution in deciding whether and how to use the concept of biosignature when thinking and communicating about habitability or life. Concepts and terms should be selected carefully and defined explicitly where appropriate. This would improve clarity and accuracy in the formulation of claims and subsequent technical and public communication about some of the most profound and important questions in science and society. With this objective in mind, we provide a checklist of questions that scientists and other interested parties should ask when assessing any reported detection of a “biosignature” to better understand exactly what is being claimed

Spectroscopic measurements on a Mukundpura meteorite grain as training for the analysis of Hayabusa2 returned samples

Sensitive laboratory instruments on Earth are capable of determining the chemical, isotopic, mineralogical, structural, and physical properties of extraterrestrial samples from the macroscopic level down to the atomic scale, allowing to determine the origin and history of the material and answer questions far beyond the reach of current robotic technology. Sample return provides us with "ground truth" about the visited body, verifying and validating conclusions that can be drawn by remote sensing (both Earth-based and by spacecraft) and via landed instruments on other bodies. Returned samples can be compared to meteorites and cosmic dust using the same instrumentation, which apart from giving us clues about where those materials come from, potentially increases their scientific value as natural space probes. And finally, returned samples can be preserved for decades and used by future generations. The detailed investigation of the mineralogy and geochemistry of Ryugu plays a fundamental role in the understanding of its formation processes, and thereby gather further knowledge about the building blocks of the solar system. Based on the preliminary data from remote sensing measurements and laboratory-based measurements, Ryugu is rich in hydrated carbonaceous chondrite (CC) like material and more specifically it is very similar to Ivuna-like (CI) carbonaceous chondrites [1]. These meteorites are characterized by a high abundance of phyllosilicates and organic matter [2], which makes them have a low albedo. However, Ryugu seems to be even darker than CIs, as well as being more porous and fragile [1].If Hayabusa2 samples are made available to our consortium, we will use a multi-pronged approach to achieve two main goals. The first goal is to address a fundamental challenge in the interpretation of remote sensing data which was seen during the initial analysis of the Hayabusa 2 samples. Observations of planetary surfaces using spectroscopy have shown subdued contrast compared to measurements performed under laboratory conditions on analog materials. A strong focus of the work performed at PSL over the last decade has been to understand - and if possible minimize - the difference between laboratory and remote sensing observations (e.g. [3,4,5,6]). Simulating the conditions on the target body as well as accurately reproducing the observing geometries have gone a long way towards that goal, however differences remain. A suggested explanation is the difference between terrestrial analog materials including even meteorites and the surfaces of planetary bodies. With Ryugu samples this hypothesis can be tested further, leading to a deeper understanding of the link between laboratory and remote sensing observations and thus benefiting not only the analysis of Hayabusa 2 data but of all remote sensing observations of planetary surfaces using spectroscopy.The second goal building on this is an investigation of the mineralogy and organic matter of the samples collected by Hayabusa 2, to better: a) understand the evolution of the materials characterizing asteroid Ryugu and therefore advance our knowledge of the mineralogy of the protoplanetary disk and organic matter (OM); b) investigate the aqueous alteration that took place in the parent body that lead to its current chemical and mineralogical characteristics; c) compare the results with data collected from pristine carbonaceous chondrite meteorites rich in hydrated minerals and organic matter.To prepare for measurements on Hayabusa 2 returned samples, we selected a small particle from the Mukundpura meteorite, a recently fallen meteorite that is considered as one of the best Ryugu analogs in the meteorite collection [7]. We have chosen a piece with a 4mm diameter, typical of the larger grains available in the Hayabusa 2 sample collection. We manufactured for this purpose a special sample holder for reflectance measurements in the FTIR spectrometer.Figure 1. (left): 4mm particle and the whole Mukundpura at PSL; (right): the 4mm particle in our sample holder.Figure 1 shows the small 4 mm selected Mukundpura particle compared with the whole sample available at PSL and its special sample holder. We adapted our standard measurement set-up reducing the aperture to fit the size of the samples. With this configuration we obtained measurements as shown in Figure 2, where MIR spectrum of the 4mm Mukundpura particle, obtained reducing the aperture of our light source beam to the minimum, 0.25 mm is compared with a measurement of the same meteorite acquired with a much larger aperture (4mm, as standard).Figure 2. Mukundpura bulk sample measured with traditional beam aperture of 4 mm (light-blue) and with reduced aperture (0.25 mm) on the small 4mm piece of the same meteorite. Below 9 µm we observe a lower reflectance of the piece compared to the bulk - reminiscent of what was observed in the preliminary investigation for the Hayabusa 2 sample.It's evident that with the reduced beam aperture, we are able to obtain high quality FTIR spectra of an Hayabusa 2 sample by just using our traditional spectroscopic set-up and compare to the thousands of spectra measured at PSL on a wide range of analogs including meteorites.Raman spectroscopy complements IR spectroscopy in the determination of the mineralogical composition of the sample. It is performed in a contactless manner, and under neutral (e.g. nitrogen) atmosphere thanks to the long working distance objective. Figure 3 shows our tests on the Mukundpura particle; different measurement modes were used to reveal the presence of olivine, carbon, and magnesium silicates.Figure 3. Example using the Mukundpura particle of an image scan of 30 points per line and 60 lines per image on a 120 x 80 µm area. The blue color denotes the presence of the olivine doublet (827 and 859 cm-1) and red the presence of carbon D and G bands (1340 and 1568 cm-1).[1] Yada, T., Abe, M., Okada, T. et al., 2022. Nat Astron 6, 214-220. [2] Cloutis, E. A., et al., 2011. Icarus, 212:1.. [3] Maturilli, A., et al., 2016a. Earth, Planets and Space 68(1). [4] Maturilli, A., et al., 2016b. Earth, Planets and Space 68(1). [5] Beck, P., et al., 2018. Icarus 313: 124-13. [6] Yesiltas, et al., 2020. Meteoritics & Planetary Science, 55(11): 2404-2421. [7] Ray, D. and Shukla, A.D., 2018. PSS 151, 149-154

Linking remote sensing, in situ and laboratory spectroscopy for a Ryugu analog meteorite sample

In 2022 JAXA issued an Announcement of Opportunity (AO) for receiving Hayabusa2 samples returned to Earth. We responded to the AO submitting a proposal based on using a multi-prong approach to achieve two main goals. The first goal is to address the subdued contrast of remote-sensing observations compared to measurements performed under laboratory conditions on analog materials. For this we will link the hyperspectral and imaging data collected from the spacecraft and the in-situ observations from the MASCOT lander instruments (MARA and MASCam) with laboratory-based measurements of Hayabusa2 samples using bi-directional reflectance spectroscopy under simulated asteroid surface conditions from UV to MIR/FIR achieved using three Bruker Vertex 80 V spectrometers in the Planetary Spectroscopy Laboratory. The second goal is the investigation of the mineralogy and organic matter of the samples collected by Hayabusa2, to better understanding the evolution of materials characterizing Ryugu and in general of protoplanetary disk and organic matter, investigating the aqueous alteration that took place in the parent body, and comparing the results with data collected from pristine carbonaceous chondrite analog meteorites. Spectral data will be complemented by Raman spectroscopy under simulated asteroid surface conditions, X-ray diffraction, would also allow us to define the bulk mineralogy of the samples as well as investigate the presence and nature of organic matter within the samples. In situ mineralogical and geochemical characterization will involve a pre-characterization of the sample fragments through scanning electron microscopy low voltage electron dispersive X-ray (EDX) maps, and micro IR analyses of the fragments. If allowed, a thin section of one grain will be used for electron microprobe analyses to geochemically characterize its mineralogical composition. To train our data collection and analysis methods on a realistic sample, we selected a piece of the Mukundpura meteorite, as one of the closer analogs to Ryugu’s surface (Ray et al., Planetary and Space Science, 2018, 151, 149–154). The Mukundpura chunk we selected for this study measures 3 mm in its maximum dimension, and we chose it so to have a test sample of the same size as the Hayabusa2 grain we requested in our proposal to JAXA’s AO. The test gave us confidence that we can measure with good SNR measurements in bi-directional reflectance for samples around 3 mm in size (see Figures 3, 4 below). To address our second goal the spectral data was complemented by Raman spectroscopy measured again under simulated asteroid surface conditions in our Raman Mineralogy and Biodetection Laboratory at DLR

Spectral investigation of volcanic alteration deposits on Vulcano island /Italy as planetary analog for acid alteration conditions on Mars

During the fifth International Summer School held on Vulcano (Eolian Islands, Italy) in June 2019 we started the investigation of volcanic deposits with different spectral instruments combining mineralogical, elemental and molecular information [1, 2]. The island of Vulcano presents an extremely large variety of volcanic products [3] in extreme acid alteration conditions. Acidic alteration may also have been a key process throughout Martian geologic history making Vulcano a perfect analog for studies on Mars by defining the geochemistry at these sites. In this work we present an update of our spectral investigations based on the VIS-NIR spectral measurements