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The cold (−13.4°C), cryoencapsulated, anoxic, interstitial brine of the >27 m thick ice of Lake Vida (Victoria Valley, Antarctica) contains 49 µg · L−1 of perchlorate and 11 µg · L−1 of chlorate. Lake Vida brine (LVBr) may provide an analog for potential oxychlorine-rich subsurface brine on Mars. LVBr volatiles were analyzed by solid-phase microextraction (SPME) gas chromatography–mass spectrometry (GC-MS) with two different SPME fibers. With the exception of volatile organic sulfur compounds, most other volatiles observed were artifacts produced in the GC injector when the thermal decomposition products of oxychlorines reacted with reduced carbon derived from LVBr and the SPME fiber phases. Analysis of MilliQ water with perchlorate (40 µg · L−1) showed low level of organic artifacts, reflecting carbon limitation. In order to observe sample-derived organic compounds, both in analog samples and on Mars, the molar abundance of reduced carbon in a sample must exceed those of O2 and Cl2 produced during decomposition of oxychlorines. This suggests that the abundance of compounds observed by the Sample Analysis at Mars (SAM) instruments in Sheepbed samples (CB-3, CB5, and CB6) may be controlled by an increase in the reduced-carbon/oxychlorine ratio of these samples. To increase chances of in situ detection of Martian organics during pyrolysis-GC-MS, we propose that the derivatization agents stored on SAM may be used as an external source of reduced carbon, increasing artificially the reduced-carbon to perchlorate ratio during pyrolysis, allowing the expression of more abundant and perhaps more diverse Martian organic matter.

We report results of an in-depth study of the morphology of small (km-scale and smaller) craters over a 4000 km2 region on Mars that includes the Phoenix landing ellipse, focused on the nature and timing of geological processes that have been active in the region. The study seeks to constrain regolith depositional rates, thickness of ground ice layer, abundance of ice in the subsurface, and the rate of crater degradation. Measurements of the size of ejecta blocks around craters show that the region has not been a net-depositional site over the last billion years. Most craters smaller than 200–350 m lack ejecta blocks regardless of age, indicating that there is a layer approximately 20–35 m deep that either does not form or does not retain ejecta blocks. This layer is expressed both within and outside the extended ejecta blanket of Heimdal crater, implying that it is not associated with the ejecta blanket. We propose that this unconsolidated layer consists dominantly of ice-cemented soil, which raises questions about the emplacement of ice at depth. We also note clear progression in crater degradation morphology, which allows us to place constraints on the rate and style of crater degradation. Small craters (20 to 200 m in diameter) appear to lose their relief due to slow infilling of the bowl over time scales of 5–100 kyr. The infilling of small craters, perhaps by a combination of ice and dust, presents a mechanism by which ice is buried down to a few tens of meters. On the other hand, larger craters (~200 m to 1 km) do not exhibit evidence for infilling, but do exhibit concentric sets of fractures within and outside the rim. We propose that loss of relief of the larger craters is due to viscous creep over time scales of a few to tens of Myr. This latter interpretation would require the presence of water ice in abundances greater than pore-filling down to depths of at least tens of meters.

The Atacama Desert is the driest and one of the most life-limiting places on Earth. Despite the extreme conditions, microbial endolithic communities have been found inside halite rocks. The presence of these microbial communities is possible due to the hygroscopic properties of evaporitic rocks composed of sodium chloride. It is important to elucidate every possible water source in such a hyperarid environment. Therefore, in the present study, an artificial neural network (ANN) based model has been designed to predict the presence of liquid water on the surface of halite pinnacles. The model predicts the moisture formation using two basic meteorological variables, air temperature, and air relative humidity. ANNs have been successfully employed for the first time as a tool for predicting the appearance of liquid water, a key factor for the endolithic microbial communities living in the driest part of the Atacama Desert. The model developed is able to correctly predict the formation of water on the surface of the halite pinnacles 83% of the cases. We anticipate the future application of this model as an important tool for the prediction of the water availability and therefore potential habitability of lithic substrates in extreme environments on Earth and perhaps elsewhere.

The future exploration of Mars will require access to the subsurface, along with acquisition of samples for scientific analysis and ground-truthing of water ice and mineral reserves for in situ resource utilization. The Icebreaker drill is an integral part of the Icebreaker mission concept to search for life in ice-rich regions on Mars. Since the mission targets Mars Special Regions as defined by the Committee on Space Research (COSPAR), the drill has to meet the appropriate cleanliness standards as requested by NASA's Planetary Protection Office. In addition, the Icebreaker mission carries life-detection instruments; and in turn, the drill and sample delivery system have to meet stringent contamination requirements to prevent false positives. This paper reports on the development and testing of the Icebreaker drill, a 1 m class rotary-percussive drill and triple redundant sample delivery system. The drill acquires subsurface samples in short, approximately 10 cm bites, which makes the sampling system robust and prevents thawing and phase changes in the target materials. Autonomous drilling, sample acquisition, and sample transfer have been successfully demonstrated in Mars analog environments in the Arctic and the Antarctic Dry Valleys, as well as in a Mars environmental chamber. In all environments, the drill has been shown to perform at the "1-1-100-100" level; that is, it drilled to 1 m depth in approximately 1 hour with less than 100 N weight on bit and approximately 100 W of power. The drilled substrate varied and included pure ice, ice-rich regolith with and without rocks and with and without 2% perchlorate, and whole rocks. The drill is currently at a Technology Readiness Level (TRL) of 5. The next-generation Icebreaker drill weighs 10 kg, which is representative of the flightlike model at TRL 5/6.

The proposed “Icebreaker” mission is a return to the Mars polar latitudes first visited by the Phoenix mission in 2007–2008. Exploring and interrogating the shallow subsurface of Mars from the surface will require some form of excavation and penetration, with drilling being the most mature approach. A series of 0.5–5 m automated rotary and rotary-percussive drills developed over the past decade by NASA Ames and Honeybee Robotics provide the capability to fly on a Mars surface mission within the next decade. Surface robotics have been integrated for sample transfer to deck instruments, and the Icebreaker sample acquisition system has been tested successfully in Mars chambers and analog field sites to depths between 1 and 3 m, most recently in the Antarctic Dry Valleys in January of 2013. This paper provides a hardware and software systems overview of the Icebreaker sample acquisition system, and discusses test results of this robotic system in relevant environments. Test results from recent Arctic and Antarctic field campaigns demonstrate a hands-off “dust to data” capability.

The high elevation valleys of the McMurdo Dry Valleys of Antarctica are the only locations on Earth known to contain dry permafrost. The Dry Valleys are a hyper-arid polar desert environment and above 1500 m elevation, air temperatures do not exceed 0 °C and thus, similarly to Mars, liquid water is largely absent and instead the hydrologic cycle is dominated by frozen ice and vapor phase processes such as sublimation. These conditions make the high elevation Dry Valleys a key Mars analog location where periglacial processes and geomorphic features, and their use as a diagnostic for subsurface ice, can be studied in situ. Two valleys in the upper Dry Valleys show a diversity of subsurface ice; University Valley is dominated by dry permafrost overlying ice-cemented to ice-bonded ground and nearby middle Beacon Valley is dominated by massive ground ice. In both cases the ice is 10–60 cm below the surface. Here we compare the surface features in these two valleys to assess any correlation with the nature of the subsurface ice and compare these features to similar features seen at the Phoenix landing site on Mars. We conclude that while surface features may be indicative of ground ice, no specific correlations are possible and more direct methods are required to determine the nature of subsurface ice on Mars.

Future exploration of the Moon will require access to the subsurface and acquisition of samples for scientific analysis and ground truthing of water-ice and mineral reserves for in situ resource utilization purposes. The LunarVader drill described in this paper is a 1-m class drill and cuttings acquisition system enabling subsurface exploration of the Moon. The drill employs rotary-percussive action, which reduces the weight on bit and energy consumption. This drilling approach has been successfully used by previous lunar missions, such as the Soviet Luna 16, 20, and 24, and United States Apollo 15, 16, and 17. These missions and drilling systems are described in detail. The passive sample acquisition system of the LunarVader drill delivers cuttings directly into a sample cup or an instrument inlet port. The drill was tested in a vacuum chamber and penetrated various formations, such as a water-saturated lunar soil simulant (JSC-1A) at −80°C, water-ice, and rocks to a depth of 1 m. The system was ...

Buried snowpack deposits are found within the McMurdo Dry Valleys of Antarctica, which offers the opportunity to study these layered structures of sand and ice within a polar desert environment. Four discrete buried snowpacks are studied within Pearse Valley, Antarctica, through in situ observations, sample analyses, O-H isotope measurements and numerical modelling of snowpack stability and evolution. The buried snowpack deposits evolve throughout the year and undergo deposition, melt, refreeze, and sublimation. We demonstrate how the deposition and subsequent burial of snow can preserve the snowpacks in the Dry Valleys. The modelled lifetimes of the buried snowpacks are dependent upon subsurface stratigraphy but are typically less than one year if the lag thickness is less than c. 7 cm and snow thickness is less than c. 10 cm, indicating that some of the Antarctic buried snowpacks form annually. Buried snowpacks in the Antarctic polar desert may serve as analogues for similar deposits on Mars and may be applicable to observations of the north polar erg, buried ice at the Mars Phoenix landing site, and observations of buried ice throughout the martian Arctic. Numerical modelling suggests that seasonal snows and subsequent burial are not required to preserve the snow and ice on Mars.

The McMurdo Dry Valleys are among the driest, coldest environments on Earth and are excellent analogues for the Martian northern plains. In preparation for the 2008 Phoenix Mars mission, we conducted an interdisciplinary investigation comparing the biological, mineralogical, chemical, and physical properties of wetter lower Taylor Valley (TV) soils to colder, drier University Valley (UV) soils. Our analyses were performed for each horizon from the surface to the ice table. In TV, clay-sized particle distribution and less abundant soluble salts both suggested vertical and possible horizontal transport by water, and microbial biomass was higher. Alteration of mica to short-order phyllosilicates suggested aqueous weathering. In UV, salts, clay-sized materials, and biomass were more abundant near the surface, suggesting minimal downward translocation by water. The presence of microorganisms in each horizon was established for the first time in an ultraxerous zone. Higher biomass numbers were seen near the surface and ice table, perhaps representing locally more clement environments. Currently, water activity is too low to support metabolism at the Phoenix site, but obliquity changes may produce higher temperatures and sufficient water activity to permit microbial growth, if the populations could survive long dormancy periods (∼106years).

Lake Untersee is one of the largest (11.4 km2) and deepest (>160 m) freshwater lakes in East Antarctica. Located at 71°S the lake has a perennial ice cover, a water column that, with the exception of a small anoxic basin in the southwest of the lake, is well mixed, supersaturated with dissolved oxygen, alkaline (pH 10.4) and exceedingly clear. The floor of the lake is covered with photosynthetic microbial mats to depths of at least 100 m. These mats are primarily composed of filamentous cyanophytes and form two distinct macroscopic structures, one of which – cm-scale cuspate pinnacles dominated by Leptolyngbya spp. – is common in Antarctica, but the second – laminated, conical stromatolites that rise up to 0.5 m above the lake floor, dominated by Phormidium spp. – has not previously been reported in any modern environment. The laminae that form the conical stromatolites are 0.2–0.8 mm in thickness consisting of fine clays and organic material; carbon dating implies that laminations may occur on near decadal timescales. The uniformly steep sides (59.6 ± 2.5°) and the regular laminar structure of the cones suggest that they may provide a modern analog for growth of some of the oldest well-described Archean stromatolites. Mechanisms underlying the formation of these stromatolites are as yet unclear, but their growth is distinct from that of the cuspate pinnacles. The sympatric occurrence of pinnacles and cones related to microbial communities with distinct cyanobacterial compositions suggest that specific microbial behaviors underpin the morphological differences in the structures.

The scarcity of liquid water in the hyperarid core of the Atacama Desert makes this region one of the most challenging environments for life on Earth. The low numbers of microbial cells in the soils suggest that within the Atacama Desert lies the dry limit for life on our planet. Here, we show that the Ca-sulfate crusts of this hyperarid core are the habitats of lithobiontic micro-organisms. This microporous, translucent substrate is colonized by epilithic lichens, as well as endolithic free-living algae, fungal hyphae, cyanobacteria and non photosynthetic bacteria. We also report a novel type of endolithic community, "hypoendoliths", colonizing the undermost layer of the crusts. The colonization of gypsum crusts within the hyperarid core appears to be controlled by the moisture regime. Our data shows that the threshold for colonization is crossed within the dry core, with abundant colonization in gypsum crusts at one study site, while crusts at a drier site are virtually devoid of life. We show that the cumulative time in 1 year of relative humidity (RH) above 60% is the best parameter to explain the difference in colonization between both sites. This is supported by controlled humidity experiments, where we show that colonies of endolithic cyanobacteria in the Ca-sulfate crust undergo imbibition process at RH >60%. Assuming that life once arose on Mars, it is conceivable that Martian micro-organisms sought refuge in similar isolated evaporite microenvironments during their last struggle for life as their planet turned arid.

A categorized water usage study was undertaken at the Flashline Mars Arctic Research Station on Devon Island, Nunavut in the High Canadian Arctic. This study was conducted as part of a long duration four-month Mars mission simulation during the summer of 2007. The study determined that the crew of seven averaged 82.07 L/day over the expedition (standard deviation 22.58 L/day). The study also incorporated a Mars Time Study phase which determined that an average of 12.12 L/sol of water was required for each crewmember. Drinking, food preparation, hand/face, oral, dish wash, clothes wash, shower, shaving, cleaning, engineering, science, plant growth and medical water were each individually monitored throughout the detailed study phases. It was determined that implementing the monitoring program itself resulted in an approximate water savings of 1.5 L/day per crewmember. The seven person crew averaged 202 distinct water draws a day (standard deviation 34) with high water use periods focusing around meal times. No statistically significant correlation was established between total water use and EVA or exercise duration. Study results suggest that current crew water utilization estimates for long duration planetary surface stays are more than two times greater than that required.

著者人数：156名, Accepted: 2008-05-27, 資料番号: SA1000998000

Drilling consists of 2 processes: breaking the formation with a bit and removing the drilled cuttings. In rotary drilling, rotational speed and weight on bit are used to control drilling, and the optimization of these parameters can markedly improve drilling performance. Although fluids are used for cuttings removal in terrestrial drilling, most planetary drilling systems conduct dry drilling with an auger. Chip removal via water-ice sublimation (when excavating water-ice-bound formations at pressure below the triple point of water) and pneumatic systems are also possible. Pneumatic systems use the gas or vaporization products of a high-density liquid brought from Earth, gas provided by an in situ compressor, or combustion products of a monopropellant. Drill bits can be divided into coring bits, which excavate an annular shaped hole, and full-faced bits. While cylindrical cores are generally superior as scientific samples, and coring drills have better performance characteristics, full-faced bits are simpler systems because the handling of a core requires a very complex robotic mechanism. The greatest constraints to extraterrestrial drilling are (1) the extreme environmental conditions, such as temperature, dust, and pressure; (2) the light-time communications delay, which necessitates highly autonomous systems; and (3) the mission and science constraints, such as mass and power budgets and the types of drilled samples needed for scientific analysis. A classification scheme based on drilling depth is proposed. Each of the 4 depth categories (surface drills, 1-meter class drills, 10-meter class drills, and deep drills) has distinct technological profiles and scientific ramifications.

We report on the analysis of high spatial resolution visible to near-infrared spectral images of Titan at Ls=240°Ls=240° in November 2000, obtained with the Space Telescope Imaging Spectrograph instrument on board the Hubble Space Telescope as part of program GO-8580. We employ a radiative transfer fractal particle aerosol model with a Bayesian parameter estimation routine that computes Titan's absolute reflectivity per pixel for 122 wavelengths by modeling the vertical distribution of the lower atmosphere haze and tropospheric methane. Analysis of these data suggests that Titan's haze concentration in the lower atmosphere varies in strength with latitude. We find Titan's tropospheric methane profile to be fairly consistent with latitude and longitude, and we find evidence for local areas of a CH4–N2 binary saturation in Titan's troposphere. Our results suggest that a methane and haze profile at one location on Titan would not be representative of global conditions.

If life ever existed on Mars, a key question is the genetic relationship of that life to life on Earth. To determine if Martian life represents a separate, second genesis of life requires the analysis of organisms, not fossils. Ancient permafrost on Mars represents one potential source of intact, albeit probably dead by radiation, Martian organisms. Strong crustal magnetism in the ancient heavily cratered southern highlands between 60 and 80°S and at about 180°W indicates what may be the oldest, best preserved ice-rich permafrost on Mars. Drilling to depths of 1000 m would reach samples unaffected by possible warming due to cyclic changes in Mars’ obliquity. When drilling into the permafrost to retrieve ancient intact Martian organisms, it is necessary to take special precautions to avoid the possibility of contamination. Earth permafrost provides an analog for Martian permafrost and convenient sites for instrument development and field testing.

A controlled airflow circulating through a coil tube maintained at sub-ambient temperatures allows moisture to condense as water droplets with subsequent adhesion onto the internal tube walls. At the same time, water droplets scavenge fine particulate matter and dissolve a fraction of the gaseous pollutants. The accumulated water in the coil is amenable for collection and chemical inspection to yield information about the presence of pollutants in the air. Based on this principle, an experimental apparatus was developed to collect and analyze ambient humidity at different sites of the Atacama Desert in Northern Chile. Moisture collection experiments lasting from 3 to 24 h were carried out with condensing temperatures ranging from −20 to 0 °C. Under all experimental conditions, the amount of collected water was between 60% and 90% of the total removable water. Sodium was present in all collected water samples and reached values up to 4 g l −1 . Practical details, theoretical considerations and the potential use of the proposed method in characterizing specific air pollutants are discussed.

Narrow-band images of Titan were obtained in November 1999 with the NASA/GSFC- built acousto-optic imaging spectrometer (AImS) camera. This instrument utilizes a tunable filter element that was used within the 500- to 1050-nm range, coupled to a CCD camera system. The images were taken with the Mount Wilson 2.54-m (100 in.) Hooker telescope, which is equipped with a natural guide star adaptive optics system. We observed Titan at 830 and 890 nm and at a series of wavelengths across the 940-nm window in Titan’s atmosphere where the methane opacity is relatively low. We determined the absolute reflectivity (I/F) of Titan and fit the values at 940 nm to a Minnaert function at Titan’s equator and at −30° latitude (closer to the subsolar point) and obtained average values for the Minnaert limb-darkening slope, k, of 0.661 ± 0.007 and 0.775 ± 0.018, respectively. Comparison with models suggests that the equatorial value of k is consistent with rain removal of haze in the lower atmosphere. The higher value of k at −30° is consistent with the southern hemisphere being brighter than the equator. However, the fits are not unique. The data and models at 890 are consistent with no limb brightening or darkening at this wavelength either at the equator or at −30°.

The Huygens Atmospheric Structure Instrument (HASI) is a multi-sensor package which has been designed to measure the physical quantities characterising the atmosphere of Titan during the Huygens probe descent on Titan and at the surface. HASI sensors are devoted to the study of Titan's atmospheric structure and electric properties, and to provide information on its surface, whether solid or liquid.

6.1 Introduction Titan appears alluringly familiar. Its surface is shaped by weather, with lakes, fluvial channels, and dunes (Tomasko et al., 2005; Lorenz et al., 2006; Stofan et al., 2007; Barnes et al., 2007; Lopes et al., 2010). Its atmosphere sports clouds that can grow to over four times the height of terrestrial thunderstorms (Griffith et al., 1998; Brown et al., 2002; Roe et al., 2002; Schaller et al., 2006a). These features result from an uncanny resemblance to Earth; similar to the terrestrial hydro-logical cycle, Titan has a methane cycle, with methane clouds, rain, and seas. On both Earth and Titan, the condensable is supplied by the surface; evaporates into the atmosphere, where it condenses into clouds; redistributes in the atmosphere; and precipitates back to the surface. These processes depend on the partitioning of solar insolation, the atmospheric structure and temperature, the condensable inventory and properties, and the circulation, all of which differ between Earth and Titan (Table 6.1). On Earth, the equivalent of 2.7 km of water covers the surface and supplies the atmosphere with the equivalent of 2.6 cm of precipitable water. This largely wet surface (70% of the globe) is heated by, on average, 60 percent of the incident sunlight, which passes through the mostly transparent (when cloudless) atmosphere. Sunlight powers weather. Its effects are direct – for example, through the evaporation of surface liquids. In addition, there are indirect impacts – for example, through differential heating across the globe, which ultimately steers the general circulation of the planet, with conditions altered locally by the variable heating associated with surface topography, land-water contrast, and other terrain heterogeneities.

Midlatitude ground ice on Mars is of significant scientific interest for understanding the history and evolution of ice stability on Mars and is relevant for human exploration as a possible in situ resource. For both science and exploration, assessing the astrobiological potential of the ice is important in terms of (1) understanding the potential for life on Mars and (2) evaluating the presence of possible biohazards in advance of human exploration. In the present study, we review the evidence for midlatitude ground ice on Mars, discuss the possible explanations for its occurrence, and assess its potential habitability. During the course of study, we systematically analyzed remote-sensing data sets to determine whether a viable landing site exists in the northern midlatitudes to enable a robotic mission that conducts in situ characterization and searches for evidence of life in the ice. We classified each site according to (1) presence of polygons as a proxy for subsurface ice, (2) presence and abundance of rough topographic obstacles (e.g., large cracks, cliffs, uneven topography), (3) rock density, (4) presence and abundance of large boulders, and (5) presence of craters. We found that a suitable landing site exists within Amazonis Planitia near ground ice that was recently excavated by a meteorite impact.

Many bodies in the outer Solar System display the presence of low albedo materials. These materials, evident on the surface of asteroids, comets, Kuiper Belt objects and their intermediate evolutionary step, Centaurs, are related to macromolecular carbon bearing materials such as polycyclic aromatic hydrocarbons and organic materials such as methanol and related light hydrocarbons, embedded in a dark, refractory, photoprocessed matrix. Many planetary rings and satellites around the outer gaseous planets display such component materials. One example, Saturn's largest satellite, Titan, whose atmosphere is comprised of around 90% molecular nitrogen N2 and less than 10% methane CH4, displays this kind of low reflectivity material in its atmospheric haze. These materials were first recorded during the Voyager 1 and 2 flybys of Titan and showed up as an optically thick pinkish orange haze layer. These materials are broadly classified into a chemical group whose laboratory analogs are termed “tholins”, after the Greek word for “muddy”. Their analogs are produced in the laboratory via the irradiation of gas mixtures and ice mixtures by radiation simulating Solar ultraviolet (UV) photons or keV charged particles simulating particles trapped in Saturn's magenetosphere. Fair analogs of Titan tholin are produced by bombarding a 9:1 mixture of N2:CH4 with charged particles and its match to observations of both the spectrum and scattering properties of the Titan haze is very good over a wide range of wavelengths. In this paper, we describe the historical background of laboratory research on this kind of organic matter and how our laboratory investigations of Titan tholin compare. We comment on the probable existence of polycyclic aromatic hydrocarbons in the Titan Haze and how biological and nonbiological racemic amino acids produced from the acid hydrolysis of Titan tholins make these complex organic compounds prime candidates in the evolution of terrestrial life and extraterrestrial life in our own Solar System and beyond. Finally, we also compare the spectrum and scattering properties of our resulting tholin mixtures with those observed on Centaur 5145 Pholus and the dark hemisphere of Saturn's satellite Iapetus in order to demonstrate the widespread distribution of similar organics throughout the Solar System. Published by Elsevier Science Ltd on behalf of COSPAR.

Saturn's large moon Titan is unique among planetary satellites in that it possesses a thick atmosphere and a haze layer that is opaque to visible light. This haze is believed to be composed of organic compounds produced by the photolysis of methane. It has been suggested that the photochemical products of methane photolysis, primarily ethane, would “rain out” over time and may produce reservoirs of liquid hydrocarbons on Titan's surface. Such material would appear very dark, with an albedo ≤0.02 (Khare et al. 1990, Bull. Am. Astron. Soc. 22 , 1033). Such low-albedo regions have not been previously detected on Titan's surface. Here we report observations of Titan at a resolution of 0.04 arcsec (0.02 arcsec/pixel) using the technique of speckle imaging from the 10-m Keck I Telescope. By observing Titan at specific infrared wavelengths which are windows through its atmosphere, we have made both an albedo map of Titan's surface at 1.6 and 2.1 μm and an estimate of Titan's haze optical depth at these wavelengths. We clearly distinguish low-albedo features (reflectance

Existing models of scattering by fractal aggregates of spheres are generally accurate but somewhat complicated and time consuming. Therefore, they are not easily usable for atmospheric studies that need intensive computations. We propose here a simple and fast model, based on Mie scattering and a set of empirical rules, that determines the scattering and absorption cross sections as well as the intensity phase function of isotropic fractal aggregates of identical spheres. This model is 10–50 times faster than the mean field model it is based on, and is easily derivable from a regular Mie code. The parameters of the present model are optimized for values of the real refractive index between 1.2 and 2.2, for imaginary refractive index less than 1 and for the product of real refractive index and spherical size parameter less than 10. This range was chosen as representative of typical particles in planetary atmospheres, for example, Titans aerosols.

Measurements of dissolved N2, O2, Ar, CO2, and CH4 were made in perennially ice-covered Lake Hoare. Results confirm previous reports that O2 concentrations in the upper water column exceed atmospheric equilibrium and that N2 and Ar are supersaturated throughout the water column. The mean supersaturation of N2 was found to be 2.0 (±0.37) and Ar was 3.8 (±1.1). The ratios of N2/Ar (20.3 ±3.8), and O2/Ar (22.5 ±4.0) at the ice-water interface are consistent with those previously measured, suggesting that bubble formation is the main process for removing gas from the lake. However, the saturations of N2 and Ar greatly exceed those previously predicted for degassing by bubble formation only at the ice-water interface. The data support the hypothesis that removal of gas by bubbles occurs in the water column to a depth of 11 m in Lake Hoare. CO2 concentration increases from near zero at the ice-water interface to 80–100 times saturation at and below the chemocline at c. 28 m. There is considerable variability in the gas concentrations throughout the water column; samples separated in depth by one metre may vary by more than 50% in gas content. It is likely that this phenomenon results from the lack of turbulent mixing in the water column. Methane (c. 2 μg 1−1) was detected below the chemocline and immediately above the sediment/water interface at a depth of 30 m. Samples from lakes Vanda, Joyce, and Miers, also show supersaturations of O2, N2, and Ar at levels similar to levels found in Lake Hoare.

Pulses of CO2 injected into the martian atmosphere more recently than 4 Ga can place the atmosphere into a stable, higher pressure, warmer greenhouse state. One to two bar pulses of CO2 added to the atmosphere during the past several billion years are sufficient to raise global mean temperatures above 240 or 250 K for tens to hundreds of millions of years, even when accounting for CO2 condensation. Over time, the added CO2 is lost to carbonates, the atmosphere collapses and returns to its buffered state. A substantial amount of water could be transported during the greenhouse periods from the surface of a frozen body of water created by outflow channel discharges to higher elevations, despite global temperatures well below freezing. This water, precipitated as snow, could ultimately form fluvial valleys if deposition sites are associated with localized heat sources, such as magmatic intrusions or volcanoes. Thus, if outflow channel discharges were accompanied by the release of sufficient quantities of CO2, a limited hydrological cycle could have resulted that would have been capable of producing geomorphic change sufficient for fluvial erosion and valley formation. Glacial or periglacial landforms would also be a consequence of such a mechanism.

Optical emissions from lightning provide information to estimate the altitude, latitude and longitude of lightning storms, the energy of the discharges, and the production of important trace species such as HCN and C2H2. Knowledge of the spectra of planetary lightning is needed to deduce the total energy dissipated by lightning (and thereby, the production of trace gases) and to help design experiments to detect and track lightning storms. Measurements of the spectral irradiance from approximately 380 to 820 nm are reported for laboratory simulations of lightning in the atmospheres of Venus, Jupiter, and Titan. In our laboratory, laser-induced plasmas (LIP) are used to simulate lightning discharges. This technique avoids contamination of the spectra by elect-ode material and maintains a safe environment while allowing the use of flammable gases, such as hydrogen and methane, found in outer planet atmospheres. The observations were made at I and 5 bars pressure for Venus and Jupiter and at 1 bar for the Titan mixture. At a pressure of one bar, our results show prominent lines from H(sub alpha), H(sub beta), H(sub gamma), and H(sub delta) lines of the Balmer Series of atomic hydrogen, a single line from Helium at 588 nm and strong continuum radiation. At pressures of 5 bars, the H(sub alpha) and H(sub beta) lines are wider, the H(sub gamma), and H(sub delta) lines merge into the continuum because of pressure broadening, and the helium line at 588 nm is no longer visible. The observed spectra of simulated lightning in the venusian atmosphere at 1 and 5 bars shows that the OI multiplet at 777.7 nm dominates the spectra, but weak features due to atomic carbon and singly excited and singly ionized oxygen atoms are also visible. Although lightning has not yet been observed on Titan, it conceivable that some form of lightning discharge could be occurring. Therefore experiments on a Titan atmosphere mixture were conducted. The most prominent features seen in the simulated spectra are the H(sub alpha) at 656 nm. from the dissociation of the methane and two strong features at 740 and 820 nm from singly excited nitrogen atoms. Most of the features between 400 and 656 nm are due to ionized nitrogen atoms. A broad, highly structured feature centered near 389 nm is molecular band radiation from CN molecules formed in the cooling plasma of atomic nitrogen, carbon, and hydrogen. It is observed in the lightning simulations of both the venusian and Titan atmospheres, For Venus, Jupiter, and Titan, narrow spectral features that are ideal for detecting lightning in the presence of sunlight are present in the spectra. These features could allow lightning to be detected and tracked by Earth-based instruments.

The collisional mechanisms of Titan's aerosols may lead to a fractal structure in which the aerosols are built by the aggregation of spherical submicrometer particles (monomers). In this initial study of the problem, the optical behavior of these aggregates is modeled assuming that each monomer radiates a dipole field in response to the incident radiation including the radiated fields of all the other elements in the aggregate. This dipole approximation, valid if the monomer radius is smaller than the wavelength, is used to calculate the scattering and extinction efficiencies of such aerosol particles, which are assumed to be composed of tholins. By applying the two-stream approximation for radiative transfer to the vertical distribution of aerosols obtained by microphysical modeling, we compute the geometric albedo of Titan. Computed values and observational values of the albedo are compared for wavelengths from 0.22 to 1.0 μm, and the effects of parameters, such as the fractal dimension of aerosols, their formation altitude or mass production rate, and, in addition, the methane abundance, are investigated. The hypothesized fractal structure of particles can explain both the visible and the UV albedos. In previous models these measurements could only be matched simultaneously under the assumption of a bimodal population. For a fractal dimension Df ≈ 2 in the settling region, corresponding to a growth governed by cluster-cluster aggregation, the computed albedo in the near-UV range matches the observations. A good fit between measurement and calculated albedo is obtained, for a formation altitude Z0 = 535 km, over the whole wavelength range by adjusting the absorption coefficient of the particles within a factor of two from that of tholins and a production rate between 0.2 and 1.5 times 3.5 × 10-13 kg m-2 sec-1. Lower formation altitudes, like our preferred case, Z0 = 385 km, cannot be investigated in the UV range due to limitations of the dipolar approximation, but we expect this case to give the same behavior.

We report observations of Titan covering the 1.075-, 1.28-, 1.6-, and 2.0-μm windows which show variations with the orbital phase, implying variability of the satellite's geometric albedo, as found earlier by other authors. The observations cover the region 4400 to 9600 cm -1 and were taken in June 1991, August 1993, and September 1994, using the Fourier transform spectrometer at the CFH Telescope (Hawaii). The resolving power was 10000, 1000, and 300 for the 1991, 1993, and 1994 spectra, respectively. The data sets cover Titan's Greatest Western Elongation and opposite Conjunctions. We find Titan's geometric albedo to be about the same (0.29) at 1.28 and 1.075 μm. (On the other hand, our observations of Uranus show the 1.28-μm albedo to be lower by 30% than that in the 1.075μm window.) The geometric albedos in the 1.6- and 2.0-μm methane windows on Titan are clearly lower (0.20 and 0.16, respectively). At the four wavelengths, a noticeable decrease in geometric albedo is observed near Greatest Western Elongation with respect to Inferior and Superior Conjunctions. The sum of the existing Titan data point to a bright leading side and a darker trailing one, with a maximum brightness near 120° (±20°) orbital longitude and a minimum near 230° (±20°). Despite important uncertainties in the value of the CH 4 absorption coefficients in the window regions, modeling Titan's observed albedos strongly suggests the existence of a surface material with a comparable albedo at 1.075 and 1.28 μm (0.4-0.5) but much darker at 1.6 and 2.0 μm (about 0.2). Titan's surface spectrum appears consistent with that of Hyperion and we suggest that this behavior may be due to the dominant presence of water ice on Titan's surface. The inhomogeneity of the surface implies that some other material (e.g., hydrocarbon lakes) is mixed with water ice in variable proportions.

The atmospheric circulation of Titan is investigated with a general circulation model. The representation of the large-scale dynamics is based on a grid point model developed and used at Laboratoire de Météorologie Dynamique for climate studies. The code also includes an accurate representation of radiative heating and cooling by molecular gases and haze as well as a parametrization of the vertical turbulent mixing of momentum and potential temperature. Long-term simulations of the atmospheric circulation are presented. Starting from a state of rest, the model spontaneously produces a strong superrotation with prograde equatorial winds (i.e., in the same sense as the assumed rotation of the solid body) increasing from the surface to reach 100 m sec-1 near the 1-mbar pressure level. Those equatorial winds are in very good agreement with some indirect observations, especially those of the 1989 occultation of Star 28-Sgr by Titan. On the other hand, the model simulates latitudinal temperature contrasts in the stratosphere that are significantly weaker than those observed by Voyager 1 which, we suggest, may be partly due to the nonrepresentation of the spatial and temporal variations of the abundances of molecular species and haze. We present diagnostics of the simulated atmospheric circulation underlying the importance of the seasonal cycle and a tentative explanation for the creation and maintenance of the atmospheric superrotation based on a careful angular momentum budget.

The surface and atmosphere of Titan constitute a system which is potentially as complex as that of the Earth, with the possibility of precipitation, surface erosion due to liquids, chemistry in large surface or subsurface hydrocarbon reservoirs, surface expressions of internal activity, and occasional major impacts leading to crustal melting. While none of the above have been observed as yet, the composition, density and thermal properties of Titan's atmosphere make it uniquely suited in the outer solar system as a place where such processes may occur. The one attribute of the Earth not expected on Titan is biological activity, which has had a profound effect on the evolution of the Earth's surface-atmosphere system. The earliest environment of Titan could have been warm enough for liquid ammonia-water solutions to exist on or near surface; pre-biotic organic processes may have taken place in such an environment. After a few hundred million years surface ammonia-water would have disappeared. Therefore, study of Titan through the Cassini-Huygens mission, planned for launch in 1997, primarily affords the opportunity to understand planet-wide surface-atmosphere interactions in the presence of fluids but in the absence of life. More speculative is the possibility that endogenic and exogenic heating continue to provide short-lived environments on Titan wherein pre-biotic organic processes in the presence of water happen.

International audience; ChemCam is a remote sensing instrument suite on board the "Curiosity" rover (NASA) that uses Laser-Induced Breakdown Spectroscopy (LIBS) to provide the elemental composition of soils and rocks at the surface of Mars from a distance of 1.3 to 7 m, and a telescopic imager to return high resolution context and micro-images at distances greater than 1.16 m. We describe five analytical capabilities: rock classification, quantitative composition, depth profiling, context imaging, and passive spectroscopy. They serve as a toolbox to address most of the science questions at Gale crater. ChemCam consists of a Mast-Unit (laser, telescope, camera, and electronics) and a Body-Unit (spectrometers, digital processing unit, and optical demultiplexer), which are connected by an optical fiber and an electrical interface. We then report on the development, integration, and testing of the Mast-Unit, and summarize some key characteristics of ChemCam. This confirmed that nominal or better than nominal performances were achieved for critical parameters, in particular power density (>1 GW/cm2). The analysis spot diameter varies from 350 μm at 2 m to 550 μm at 7 m distance. For remote imaging, the camera field of view is 20 mrad for 1024×1024 pixels. Field tests demonstrated that the resolution (˜90 μrad) made it possible to identify laser shots on a wide variety of images. This is sufficient for visualizing laser shot pits and textures of rocks and soils. An auto-exposure capability optimizes the dynamical range of the images. Dedicated hardware and software focus the telescope, with precision that is appropriate for the LIBS and imaging depths-of-field. The light emitted by the plasma is collected and sent to the Body-Unit via a 6 m optical fiber. The companion to this paper (Wiens et al. this issue) reports on the development of the Body-Unit, on the analysis of the emitted light, and on the good match between instrument performance and science specifications.

Lake Untersee is one of the largest (11.4 km(2)) and deepest (160 m) freshwater lakes in East Antarctica. Located at 71°S the lake has a perennial ice cover, a water column that, with the exception of a small anoxic basin in the southwest of the lake, is well mixed, supersaturated with dissolved oxygen, alkaline (pH 10.4) and exceedingly clear. The floor of the lake is covered with photosynthetic microbial mats to depths of at least 100 m. These mats are primarily composed of filamentous cyanophytes and form two distinct macroscopic structures, one of which--cm-scale cuspate pinnacles dominated by Leptolyngbya spp.--is common in Antarctica, but the second--laminated, conical stromatolites that rise up to 0.5 m above the lake floor, dominated by Phormidium spp.--has not previously been reported in any modern environment. The laminae that form the conical stromatolites are 0.2-0.8 mm in thickness consisting of fine clays and organic material; carbon dating implies that laminations may occur on near decadal timescales. The uniformly steep sides (59.6 ± 2.5°) and the regular laminar structure of the cones suggest that they may provide a modern analog for growth of some of the oldest well-described Archean stromatolites. Mechanisms underlying the formation of these stromatolites are as yet unclear, but their growth is distinct from that of the cuspate pinnacles. The sympatric occurrence of pinnacles and cones related to microbial communities with distinct cyanobacterial compositions suggest that specific microbial behaviors underpin the morphological differences in the structures.

As humans venture back to the Moon, or onward to near-Earth objects and Mars, it is expected that the rigors of this exploration will far exceed those of Apollo. Terrestrial analogs can play a key role in our preparations for these complex voyages, since in addition to their scientifi c value, analogs afford the exploration community a means to safely prepare and test exploration strategies for future robotic and human planetary missions. Many relevant analog studies exist, and each is focused on a particular aspect of strategic development. Some analog programs such as the Pavilion Lake Research Project (PLRP) present the opportunity to investigate both real scientifi c and real exploration scenarios in tandem. The activities of this research program demand the use of techniques, tools, and strategies for underwater scientifi c exploration, and the challenges associated with the scientifi c exploration of Pavilion Lake are analogous to those human explorers will encounter on other planetary and small solar system bodies. The goal of this paper is to provide a historical synopsis of the PLRP’s objectives, milestones, and contributions to both the scientifi c and exploration community. Here, we focus on detailing the development and deployment of an integrated science and exploration program with analog application to our understanding of early Earth systems and the preparation for future human space exploration. Over a decade of exploration and discovery is chronicled herein. Spec483_CH07_p085-116.indd 86 29/09/11 7:13 PM A historical overview of the Pavilion Lake Research Project 87 spe 483-01 page 87 THE SCIENTIFIC DISCOVERY OF PAVILION LAKE

There is evidence that at one time Mars had liquid water habitats on its surface. Studies of microbial communities in cold and dry environments on the Earth provide a basis for discussion of the possible nature of any life that may have existed on Mars during that time. Of particular relevance are the cyanobacterial communities found in hypolithic and endolithic habitats in deserts. Microbial mats found under ice-covered lakes provide an additional possible Martian system. Results obtained from these field studies can be used to guide the search for fossil evidence of life on Mars. It is possible that in the future life will be reintroduced on Mars in an effort to restore that planet to habitable conditions. In this case the organisms under study as exemplars of past life may provide the hardy stock of pioneering Martian organisms. These first organisms must be followed by plants. The feasibility of reviving Mars will depend on the ability of plants to grow in an abundance of CO2 but at extremely...

Forthcoming human planetary exploration will require increased scientific return (both in real time and post-mission), longer surface stays, greater geographical coverage, longer and more frequent EVAs, and more operational complexities than during the Apollo missions. As such, there is a need to shift the nature of astronauts’ scientific capabilities to something akin to an experienced terrestrial field scientist. To achieve this aim, the authors present a case that astronaut training should include an Apollo-style curriculum based on traditional field school experiences, as well as full immersion in field science programs. Herein we propose four Learning Design Principles (LDPs) focused on optimizing astronaut learning in field science settings. The LDPs are as follows: (1) LDP#1: Provide multiple experiences: varied field science activities will hone astronauts’ abilities to adapt to novel scientific opportunities (2) LDP#2: Focus on the learner: fostering intrinsic motivation will orient astronauts towards continuous informal learning and a quest for mastery (3) LDP#3: Provide a relevant experience—the field site: field sites that share features with future planetary missions will increase the likelihood that astronauts will successfully transfer learning (4) LDP#4: Provide a social learning experience—the field science team and their activities: ensuring the field team includes members of varying levels of experience engaged in opportunities for discourse and joint problem solving will facilitate astronauts’ abilities to think and perform like a field scientist. The proposed training program focuses on the intellectual and technical aspects of field science, as well as the cognitive manner in which field scientists experience, observe and synthesize their environment. The goal of the latter is to help astronauts develop the thought patterns and mechanics of an effective field scientist, thereby providing a broader base of experience and expertise than could be achieved from field school alone. This will enhance their ability to execute, explore and adapt as in-field situations require.

Robotic platforms are essential for future human planetary and lunar exploration as they can operate in more extreme environments with a greater endurance than human explorers. In this era of space exploration, a terrestrial analog that can be used for development of the coordination between manned and robotic vehicles will optimize the scientific return of future missions while concurrently minimizing the downtime of both human explorers and robotic platforms. This work presents the use of underwater exploratory robots – autonomous underwater vehicles (AUV), remotely operated vehicles (ROV), and manned submersibles – as analogues for mixed human–robot exploration of space. Subaqueous settings present diverse challenges for navigation, operation and recovery that require the development of an exploration model of a similar complexity as required for space exploration. To capitalize on the strengths of both robotic and human explorers this work presents lessons learnt with respect to the fields of human–robotic interface (HRI) and operator training. These are then used in the development of mission evaluation tools: (1) a task efficiency index (TEI), (2) performance metrics, and (3) exploration metrics. Although these independent evaluations were useful for specific missions, further refinement will be required to fully evaluate the strengths and capabilities of multiple platforms in a human–robotic exploration campaign in order to take advantage of unforeseen science opportunities in remote settings.