Exobiological exploration of Mars.

Of all the other planets in the solar system, Mars remains the most promising for further elucidating concepts about chemical evolution and the origin of life. Strategies were developed to pursue three exobiological objectives for Mars exploration: determining the abundance and distribution of the biogenic elements and organic compounds, detecting evidence of an ancient biota on Mars, and determining whether indigenous organisms exist anywhere on the planet. The three strategies are quite similar and, in fact, share the same sequence of phases. In the first phase, each requires global reconnaissance and remote sensing by orbiters to select sites of interest for detailed in situ analyses. In the second phase, lander missions are conducted to characterize the chemical and physical properties of the selected sites. The third phase involves conducting "critical" experiments at sites whose properties make them particularly attractive for exobiology. These critical experiments would include, for example, identification of organics, detection of fossils, and detection of extant life. The fourth phase is the detailed analysis of samples returned from these sites in Earth-based laboratories to confirm and extend previous discoveries. Finally, in the fifth phase, human exploration is needed to establish the geological settings for the earlier findings or to discover and explore sites that are not accessible to robotic spacecraft.     

Characteristics and formation of amino acids and hydroxy acids of the Murchison meteorite.

Eight characteristics of the unique suite of amino acids and hydroxy acids found in the Murchison meteorite can be recognized on the basis of detailed molecular and isotopic analyses. The marked structural correspondence between the alpha-amino acids and alpha-hydroxy acids and the high deuterium/hydrogen ratio argue persuasively for their formation by aqueous phase Strecker reactions in the meteorite parent body from presolar, i.e., interstellar, aldehydes, ketones, ammonia, and hydrogen cyanide. The characteristics of the meteoritic suite of amino acids and hydroxy acids are briefly enumerated and discussed with regard to their consonance with this interstellar-parent body formation hypothesis. The hypothesis has interesting implications for the organic composition of both the primitive parent body and the presolar nebula.     

Galactic cosmic rays and cell-hit frequencies outside the magnetosphere.

An evaluation of the exposure of space travelers to galactic cosmic radiation outside the earth's magnetosphere is made by calculating fluences of high-energy primary and secondary particles with various charges traversing a sphere of area 100 microns2. Calculations relating to two shielding configurations are presented: the center of a spherical aluminum shell of thickness 1 g/cm2, and the center of a 4 g/cm2 thick aluminum spherical shell within which there is a 30 g/cm2 diameter spherical water phantom with the point of interest 5 g/cm2 from the surface. The area of 100 microns2 was chosen to simulate the nucleus of a cell in the body. The frequencies as a function of charge component in both shielding configurations reflects the odd-even disparity of the incident particle abundances. For a three-year mission, 33% of the cells in the more heavily shielded configuration would be hit by at least one particle with Z greater than 10. Six percent would be hit by at least two such particles. This emphasizes the importance of studying single high-Z particle effects both on cells which might be "at risk" for cancer induction and on critical neural cells or networks which might be vulnerable to inactivation by heavy charged particle tracks. Synergistic effects with the more numerous high-energy protons and helium ions cannot be ruled out. In terms of more conventional radiation risk assessment, the dose equivalent decreased by a factor of 2.85 from free space to that in the more heavily shielded configuration. Roughly half of this was due to the decrease in energy deposition (absorbed dose) and half to the decrease in biological effectiveness (quality factor).     

Engineering concepts for inflatable Mars surface greenhouses.

A major challenge of designing a bioregenerative life support system for Mars is the reduction of the mass, volume, power, thermal and crew-time requirements. Structural mass of the greenhouse could be saved by operating the greenhouse at low atmospheric pressure. This paper investigates the feasibility of this concept. The method of equivalent system mass is used to compare greenhouses operated at high atmospheric pressure to greenhouses operated at low pressure for three different lighting methods: natural, artificial and hybrid lighting.     

Continuous tracking of cmes using MICA, andLASCO C2 and C3 coronagraphs

In this work we have tracked coronal mass ejections observed with the ground based Mirror Coronagraph for Argentina (MICA) and the Large Angle and Spectroscopic Coronagraph (LASCO) C2 and C3 on board of the Solar and Heliospheric Observatory (SOHO). The MICA telescope is located at El Leoncito (31.8 S, 69.3 W), San Juan (Argentina), since 1997 as part of a bilateral scientific project between Germany and Argentina. SOHO is a project of international cooperation between ESA and NASA. Together these instruments are able to observe the solar corona ranging from 1.05 to 32 solar radii. MICA images the Fe XIV emission line corona and LASCO coronagraphs observe the Thomson scattered white light corona. We have selected events for which there are observations from the three coronagraphs. Using the composite data we were able to obtain height-time diagrams for the corresponding dynamical coronal features traveling outwards in order to determine some of their kinematical properties, i.e., plane of sky velocity and acceleration.     

Automorphogenesis and gravitropism of plant seedlings grown under microgravity conditions.

Plant seedlings exhibit automorphogenesis on clinostats. The occurrence of automorphogenesis was confirmed under microgravity in Space Shuttle STS-95 flight. Rice coleoptiles showed an inclination toward the caryopsis in the basal region and a spontaneous curvature in the same adaxial direction in the elongating region both on a three-dimensional (3-D) clinostat and in space. Both rice roots and Arabidopsis hypocotyls also showed a similar morphology in space and on the 3-D clinostat. In rice coleoptiles, the mechanisms inducing such an automorphic curvature were studied. The faster-expanding convex side of rice coleoptiles showed a higher extensibility of the cell wall than the opposite side. Also, in the convex side, the cell wall thickness was smaller, the turnover of the matrix polysaccharides was more active, and the microtubules oriented more transversely than the concave side, and these differences appear to be causes of the curvature. When rice coleoptiles grown on the 3-D clinostat were placed horizontally, the gravitropic curvature was delayed as compared with control coleoptiles. In clinostatted coleoptiles, the corresponding suppression of the amyloplast development was also observed. Similar results were obtained in Arabidopsis hypocotyls. Thus, the induction of automorphogenesis and a concomitant decrease in graviresponsiveness occurred in plant shoots grown under microgravity conditions.     

Surface tension-driven flows in horizontal liquid metal layers

The problem of surface tension-driven flows in horizontal liquid layers has been studied experimentally, and theoretically by direct numerical simulation and small perturbation analysis. We focus our attention on situations in which the depth of the fluid (liquid tin; small Prandtl number, Pr=0.015) is small enough to ensure the predominance of the surface tension forces over those due to the buoyancy. The surface velocity has been experimentally obtained for liquid tin layer with various aspect ratio (length to height) in the range 5<A<83. The thermal gradients are ranged from 5 to 40°K/cm. In the numerical study, the Navier-Stokes and energy equations are solved by an efficient finite difference technique. The parameters governing the flow behaviour in the liquid are varied to determine their effects on thermocapillary convection: the Reynolds number 10<Re<210⁴ and the aspect ratio 2<A<25; with Pr kept constant at Pr=0.015. The linear eigenequation resulting from small spatial disturbances of the Couette flow solution is solved using an Tau-Chebyshev approximation. A notable feature of the theoretical study is the totally different end circulations. In the region near the cold wall a multicell structure is evident. This agrees with the eigensolution which is of complex type, indicating spatial periodicity. In the hot wall region the flow is accelerated to reach the velocity value for the fully-developed Couette flow which is reached under conditions such as Re/A<20. The transition from viscous to boundary layer regime occurs for a critical value (Re/A)_c of nearly about 200, as deduced from the numerical and experimental results.     

Distribution of calmodulin in corn seedlings: Immunocytochemical localization in coleoptiles and root apices

Immunofluorescence techniques have been used to study the distribution of calmodulin in several tissues in etiolated corn ( , var. Bear Hybrid) seedlings. Uniform staining was seen in the background cytoplasm of most cell types. Cell walls and vacuoles were not stained. In coleoptile mesophyll cells the nucleoplasm of most nuclei was stained as was the stroma of most amyloplasts. The lumen border of mature tracheary elements in coleoptiles also stained. In the rootcap the most intensely stained regions were the cytoplasms of columella cells and of the outermost cells enmeshed in the layer of secreted slime. Nuclei in the rootcap cells did not stain distinctly, but those in all cell types of the root meristem did. Also in the root meristem, the cytoplasm of metaxylem elements stained brightly. These results are compared and contrasted with previous data on the localization of calmodulin in pea root apices and epicotyls and discussed in relation to current hypotheses on mechanisms of gravitropism.     

The potential of the lichen symbiosis to cope with the extreme conditions of outer space II: germination capacity of lichen ascospores in response to simulated space conditions.

Complementary to the already well-studied microorganisms, lichens, symbiotic organisms of the mycobiont (fungi) and the photobiont (algae), were used as "model systems" in which to examine the ecological potential to resist to extreme environments of outer space. Ascospores (sexual propagules of the mycobiont) of the lichens Fulgensia bracteata, Xanthoria elegans and Xanthoria parietina were exposed to selected space-simulating conditions (up to 16 h of space vacuum at 10(-3) Pa and UV radiation at 160 nm < or = lambda < or = 400 nm), while embedded in the lichen fruiting bodies. After exposure, the ascospores were discharged and their viability was tested as germination capacity on different culture media including those containing Mars regolith simulant. It was found that (i) the germination rate on media containing Mars regolith simulant was as high as on other mineral-containing media, (ii) if enclosed in the ascocarps, the ascospores survived the vacuum exposure, the UV-irradiation as well as the combined treatment of vacuum and UV to a high degree. In general, 50 % or more viable spores were recovered, with ascospores of X. elegans showing the highest survival. It is suggested that ascospores inside the ascocarps are well protected by the anatomical structure, the gelatinous layer and the pigments (parietin and carotene) against the space parameters tested.     

A first step towards proton flux forecasting

We present a preliminary version of a potential tool for real time proton flux prediction which provides proton flux profiles and cumulative fluence profiles at 0.5 and 2 MeV of solar energetic particle events, from their onset up to the arrival of the interplanetary shock at the spacecraft position (located at 1 or 0.4 AU). Based on the proton transportation model by Lario et al. [Lario, D., Sanahuja, B., Heras, A.M. Energetic particle events: efficiency of interplanetary shocks as 50 keV E < 100 MeV proton accelerators. Astrophys. J. 509, 415–434, 1998] and the magnetohydrodynamic shock propagation model of Wu et al. [Wu, S.T., Dryer, M., Han, S.M. Non-planar MHD model for solar flare-generated disturbances in the Heliospheric equatorial plane. Sol. Phys. 84, 395–418, 1983], we have generated a database containing “synthetic” profiles of the proton fluxes and cumulative fluences of 384 solar energetic particle events. We are currently validating the applicability of this code for space weather forecasting by comparing the resulting “synthetic” flux profiles with those of several real events.