Microbiological activities can be detected in various extreme environments on Earth, which suggest that extraterrestrial environments, such as on Mars, could host life. There have been proposed a number of biomarkers to detect extant life mostly based on specific molecules. Because terrestrial organisms have catalytic proteins (enzymes), enzymatic activity may also be a good indicator to evaluate biological activities in extreme environments. Phosphatases are essential for all terrestrial organisms because phosphate esters are ubiquitously used in genetic molecules (DNA/RNA) and membranes. In this study, we evaluated microbial activity in soils of the Atacama Desert, Chile, by analysing several biomarkers, including phosphatase activity. Phosphatases extracted with Tris buffer were assayed fluorometrically using 4-methylumbelliferyl phosphate as a substrate. The horizontal distribution of phosphatase activity and other parameters in soils from the Atacama Desert showed that phosphatase activity was positively correlated with amino acid concentration and colony-forming units and negatively correlated with precipitation amount. We found consistent that biochemical indicators including phosphatase significantly decreased in the extreme hyper-arid zone where rainfall of <25 mm year−1. The results were compared with phosphatase activities detected in extreme environments, such as submarine hydrothermal systems and Antarctic soils, as well as soils from ordinary environments. Overall, our results suggested that phosphatase activity could be a good indicator for evaluating biological activities in extreme environments.

Titan, the largest satellite of Saturn, has a thick atmosphere containing nitrogen and methane. A variety of organic compounds have been detected in the atmosphere, most likely produced when atmospheric gases are exposed to ultraviolet light, electrons captured by the magnetosphere of Saturn and cosmic rays. The Cassini/Huygens probe showed that the average temperature on the surface of Titan is 93.7 K, with lakes of liquid ethane and methane. Sub-surface mixtures of liquid ammonia and water may also be present. We have synthesized complex organic compounds (tholins) by exposing a mixture of nitrogen and methane to plasma discharges, and investigated their interactions with several different liquids that simulate Titan's liquidosphere. We found that coacervates formed when tholins were extracted in non-polar solvents followed by exposure to aqueous ammonia solutions. The results suggest that coacervates can self-assemble in Titan's liquidosphere which have the potential to undergo further chemical evolution. Similar processes are likely to occur in the early evolution of habitable planets when tholin-like compounds undergo phase separation into microscopic structures dispersed in a suitable aqueous environment.

A wide variety of organic compounds have been found in carbonaceous chondrites and comets, which suggests that extraterrestrial organic compounds could have been an important source of the first terrestrial biosphere. In the Greenberg model, these organic compounds in the small bodies were originally formed in interstellar dusts (ISD) in dense clouds by the action of cosmic rays and ultraviolet light. We irradiated a frozen mixture of methanol, ammonia and water with high-energy heavy ions from an accelerator (“HIMAC” in NIRS, Japan) to simulate the action of cosmic rays in dense clouds. Racemic mixtures of amino acids were detected after hydrolysis of the irradiation products. A mixture of carbon monoxide, ammonia and water also gave such complex amino acid precursors with large molecular weights. When such amino acid precursors were irradiated with circular polarized UV light from a synchrotron, enantiomeric excesses were detected. The yield of amino acids was not largely changed between, before, and after CPL-irradiation. The present results suggest that the seed of homochirality of terrestrial amino acids were originally formed in interstellar space.

Rayleigh surface wave velocities in Ag/Cr and Au/Cr metallic superlattices have been measured by Brillouin scattering spectroscopy. These metallic superlattices were prepared by the metal-MBE method. X-ray diffraction measurements indicated that the structures of Ag/Cr and Au/Cr superlattices were almost the same. In the Au/Cr superlattices a maximum in a plot of surface wave velocities as a function of the bilayer thickness was observed. On the contrary, a distinct dip was shown in Ag/Cr systems. This anomalous behavior of the sound velocity could not be attributed to the expansion and the contraction of the lattices. Differences in atomic scale structure in the interface seem to play a major role in these systems.

The intensity oscillation of reflection high-energy electron diffraction (RHEED) during the autoepitaxy of Au on Au(001) and Ag on Ag(001) and during the heteroepitaxy of Au on Ag(001) and Ag on Au(001) were measured at 310 and 330 K. The morphologies of the growing surfaces are discussed in terms of the surface energies and the surface reconstruction. RHEED intensity oscillation during Au deposition on Ag(001) at 330 K rapidly decayed at the 6th period when reconstruction of the Au(001) surface appeared. Such a rapid decay was not observed at 310 K. On the other hand, the reconstruction entirely disappeared at the first minimum of the RHEED intensity oscillation in the case of Ag deposition on Au.

The results of x-ray diffraction, resistivity and magnetization measurements of Ag/Cr metallic superlattices are presented. Dramatic changes in the interplanar distances of Ag and Cr were found as a function of the number of Cr monolayers in a period. The resistivities of the superlattices increased as the composition of Cr increased. Magnetization measurements show that the superlattice [Ag(10ML)/Cr(2ML)] exibits a maximum magnetic susceptibility.

The Hall effect on Ag/Cr superlattice system has been investigated. When the Cr layer thickness is changed from 1 monolayer (ML) to 6ML for the same Ag layer thickness of 10 ML, the Hall coefficient (RH) varies anomalously. For 1 ML Cr sample, we obtained RH value close to that of pure Ag as expected. The absolute value of RH is enhanced with increasing Cr layer thickness. After having a negative peak near 3 ML Cr, it decreases at larger Cr thicknesses. The field dependence of the Hall resistivity is linear for all the samples, and there is no sign of long range magnetic order down to 1.5K.

Ag/Cr metallic superlattices with bilayer thickness in the range of 17–136Å were prepared by metal-MBE method. X-ray diffraction measurements indicated that the thickness fluctuations of each layer were rather small. The lattice matching at the interface between Ag(100) and Cr(100) is almost perfect. But, the interplanar spacings of Ag(100) and Cr(100) changed as a function of bilayer thickness. Surface wave velocities have been measured using Brillouin spectroscopy. In contrast to Au/Cr superlattices which show a hardening, a plot of surface wave velocities as a function of the bilayer thickness in Ag/Cr superlattices showed a distinct dip.