SignificanceIt has remained an unresolved question whether microorganisms recovered from the most arid environments on Earth are thriving under such extreme conditions or are just dead or dying vestiges of viable cells fortuitously deposited by atmospheric processes. Based on multiple lines of evidence, we show that indigenous microbial communities are present and temporally active even in the hyperarid soils of the Atacama Desert (Chile). Following extremely rare precipitation events in the driest parts of this desert, where rainfall often occurs only once per decade, we were able to detect episodic incidences of biological activity. Our findings expand the range of hyperarid environments temporarily habitable for terrestrial life, which by extension also applies to other planetary bodies like Mars.

We report Raman, infrared, and x-ray diffraction (XRD) measurements, along with ab initio calculations on formic acid (FA) under pressure up to 50 GPa. We find an infinite chain Pna2(1) structure to be a high-pressure phase at room temperature. Our data indicate the symmetrization and a partially covalent character of the intrachain hydrogen bonds above approximately 20 GPa. Raman spectra and XRD patterns indicate a loss of long-range order at pressures above 40 GPa, with a large hysteresis upon decompression. We attribute this behavior to a three-dimensional polymerization of FA.

The infrared response of coronene (C(24)H(12)) under pressure and temperature conditions up to 10 GPa and 300 °C is examined in situ using a diamond anvil cell and synchrotron-source Fourier transform infrared (FTIR) spectroscopy. Coronene is a polycyclic aromatic hydrocarbon that is present in the interstellar medium and meteorites which may have contributed to the Earth's primordial carbon budget. It appears to undergo a reversible phase transition between 2 and 3.2 GPa at ambient temperature; new intramolecular bonds in the region 840-880 cm(-1) result from compression. We document the shift of spectral features to higher wavenumbers with increasing pressure but find this change suppressed by increased temperature. By investigating the stability of coronene over a range of naturally occurring conditions found in a range of environments, we assess the survival of the molecule through various terrestrial and extraterrestrial processes. Coronene has previously been shown to survive atmospheric entry during Earth accretion; this can now be extended to include survival through geological processes such as subduction and silicate melting of the rock cycle, opening the possibility of extraterrestrial coronene predating terrestrial accretion existing on Earth.

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The detection of chlorinated hydrocarbons by Curiosity on Mars has been attributed to the presence of unidentified indigenous organic matter. Similarly, oxychlorines on Earth have been proposed to be responsible for the apparent lack of organics in the Atacama Desert. The presence of perchlorate (ClO 4 -) poses a unique challenge to the measurement of organic matter due to the oxidizing power of oxychlorines during commonly used pyrolysis-gas chromatography-mass spectrometry (py-GC-MS) methods. Here, we show that perchlorates and other oxyanion salts inhibit the detection of organic compounds, but that removing these problematic species prior to pyrolysis by using an optimal sample extraction duration and suitable ratios of water to sample mass enables analysis. We have characterized leached and unleached samples containing perchlorates from the Atacama Desert and have found that after leaching, the py-GC-MS chromatograms of the dried mineral residues show identifiable biomarkers associated with indigenous cyanobacteria. Samples which were pyrolyzed without leaching showed no detectable organic matter other than background siloxane and very weak or no trace of detectable polychlorinated benzenes Dried sample residues remaining after leaching, the mineral matrix and water-insoluble organic matter, showed a strong organic response in all cases when analyzed by py-GC-MS. These residues are most likely the product of the pyrolysis of water insoluble organics originally present in the samples. In addition, our results imply that previous soil analyses which contained high levels of oxyanions and concluded that organics were either not present, or at extremely low levels, should be re-examined.

We have determined the melting temperature of formic acid(HCOOH) to 8.5 GPa using infrared absorption spectroscopy, Raman spectroscopy and visual observation of samples in a resistively heated diamond-anvil cell. The experimentally determined melting curve compares favorably with a twophase thermodynamic model. Decomposition reactions were observed above the melting temperature up to a pressure of 6.5 GPa, where principal products were CO 2 , H 2 O and CO. At pressures above 6.5 GPa, decomposition led to solid-like reaction products. Infrared and Raman spectra of these recovered products indicate that pressure affects the nature of carbon-carbon bonding.

The search for life on Mars targets the detection of organic matter from extant or extinct organisms. Current protocols use thermal extraction procedures to transfer organic matter to mass spectrometer detectors. Oxidizing minerals on Mars, such as perchlorate, interfere with organic detection by thermal extraction. Thermal decomposition of perchlorate releases oxygen, which promotes combustion of organic carbon. We have assessed the minimum mass ratio of organic carbon to perchlorate required to detect organic matter by thermal extraction and mass spectrometry. Locations on Mars with organic carbon to perchlorate ratios above 4.7-9.6 should be targeted. Because habitability is enhanced by the presence of liquid water and because perchlorate is a water-soluble salt, locations on Mars with evidence of past or recent liquid water are high priority targets.Plain Language Summary Missions to Mars look for evidence of organic molecules using thermal extraction techniques. Certain minerals on the Martian surface, such as perchlorate salts, break down during heating, releasing oxygen and causing the combustion of any organic matter, which may have been present. In this event organic carbon is lost to analysis as CO and CO 2 . We used the ratio of CO: CO 2 produced as a proxy for the completeness of combustion when various ratios of organic matter and perchlorate where thermally decomposed together. This allowed us to find a minimum organic carbon: perchlorate mass ratio (~5 times) for the survival of organic molecules. Carbon monoxide can only be produced if there is an excess of carbon to oxygen, which could enable the survival of unoxidized organic molecules for their subsequent detection. Applying these findings to Mars suggests that we would not expect to be able to detect organic molecules in average Martian soil. Consequently, future life detection missions to Mars must search for areas that exceed this ratio, either by having more organic matter or less perchlorate, and locations with evidence of recent water activity or in the subsurface are most likely to fulfill both of these criteria.

Simple n-alcohols, such as 1-dodecanol, show anomalous film-forming and friction behaviour in the elastohydrodynamic lubrication (EHL) contacts inside bearings and gears. Using tribometer, diamond anvil cell (DAC), and differential scanning calorimetry (DSC) experiments, we show that 1-dodecanol undergoes pressure-induced solidification when entrained into EHL contacts. Different solid polymorphs are formed inside the contact depending on the temperature and pressure conditions. Surprisingly, at moderate temperature and pressure, 1-dodecanol forms a polymorph that exhibits robust macroscale superlubricity. The DAC and DSC experiments show that superlubricity is facilitated by the formation of lamellar, hydrogen-bonded structures of hexagonally close-packed molecules, which promote interlayer sliding. This novel superlubricity mechanism is similar to that proposed for the two-dimensional materials commonly employed as solid lubricants, but it enables the practical advantages of liquid lubricants to be maintained. When the pressure is increased, 1-dodecanol undergoes a polymorphic transformation into a phase that gives higher friction. The DAC and DSC experiments indicate that the high-friction polymorph is an orthorhombic crystal. The polymorphic transformation pressure coincides with the onset of dimple formation in the EHL films, suggesting that the anomalous film shapes are caused by the formation of rigid orthorhombic crystals inside the contact. The unusual friction and film-formation behaviour of 1-dodecanol result from bulk effects that are insensitive to the surface chemistry or topology. This is the first demonstration of macroscale superlubricity inside EHL contacts using a non-aqueous lubricant. This discovery creates the possibility of implementing superlubricity in a wide range of machine components, which would result in enormous improvements in efficiency and durability. File list (2) download file view on ChemRxiv Alcohol Superlubricity paper-revised-clean.pdf (1.44 MiB) download file view on ChemRxiv Supporing Information-final.pdf (1.05 MiB)