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841.
Microorganisms have been found to etch volcanic glass within volcaniclastic deposits from the Ontong Java Plateau, creating micron-sized tunnels and pits. The fossil record of such bioalteration textures is interpreted to extend back ~3.5 billion years to include meta-volcanic glass from ophiolites and Precambrian greenstone belts. Bioalteration features within glass clasts from Leg 192 of the Ocean Drilling Program were investigated through optical microscopy and Fourier transform infrared (FTIR) spectroscopy of petrographic thin sections. Extended depth of focus optical microscopic imaging was used to identify bioalteration tubules within the samples and later combined with FTIR spectroscopy to study the organic molecules present within tubule clusters. The tubule-rich areas are characterized by absorption bands indicative of aliphatic hydrocarbons, amides, esters, and carboxylic groups. FTIR analysis of the tubule-free areas in the cores of glass clasts indicated that they were free of organics. This study further constrains the nature of the carbon compounds preserved within the tubules and supports previous studies that suggest the tubules formed through microbial activity. 相似文献
842.
Northup DE Melim LA Spilde MN Hathaway JJ Garcia MG Moya M Stone FD Boston PJ Dapkevicius ML Riquelme C 《Astrobiology》2011,11(7):601-618
Lava caves contain a wealth of yellow, white, pink, tan, and gold-colored microbial mats; but in addition to these clearly biological mats, there are many secondary mineral deposits that are nonbiological in appearance. Secondary mineral deposits examined include an amorphous copper-silicate deposit (Hawai'i) that is blue-green in color and contains reticulated and fuzzy filament morphologies. In the Azores, lava tubes contain iron-oxide formations, a soft ooze-like coating, and pink hexagons on basaltic glass, while gold-colored deposits are found in lava caves in New Mexico and Hawai'i. A combination of scanning electron microscopy (SEM) and molecular techniques was used to analyze these communities. Molecular analyses of the microbial mats and secondary mineral deposits revealed a community that contains 14 phyla of bacteria across three locations: the Azores, New Mexico, and Hawai'i. Similarities exist between bacterial phyla found in microbial mats and secondary minerals, but marked differences also occur, such as the lack of Actinobacteria in two-thirds of the secondary mineral deposits. The discovery that such deposits contain abundant life can help guide our detection of life on extraterrestrial bodies. 相似文献
843.
Schulze-Makuch D Méndez A Fairén AG von Paris P Turse C Boyer G Davila AF António MR Catling D Irwin LN 《Astrobiology》2011,11(10):1041-1052
In the next few years, the number of catalogued exoplanets will be counted in the thousands. This will vastly expand the number of potentially habitable worlds and lead to a systematic assessment of their astrobiological potential. Here, we suggest a two-tiered classification scheme of exoplanet habitability. The first tier consists of an Earth Similarity Index (ESI), which allows worlds to be screened with regard to their similarity to Earth, the only known inhabited planet at this time. The ESI is based on data available or potentially available for most exoplanets such as mass, radius, and temperature. For the second tier of the classification scheme we propose a Planetary Habitability Index (PHI) based on the presence of a stable substrate, available energy, appropriate chemistry, and the potential for holding a liquid solvent. The PHI has been designed to minimize the biased search for life as we know it and to take into account life that might exist under more exotic conditions. As such, the PHI requires more detailed knowledge than is available for any exoplanet at this time. However, future missions such as the Terrestrial Planet Finder will collect this information and advance the PHI. Both indices are formulated in a way that enables their values to be updated as technology and our knowledge about habitable planets, moons, and life advances. Applying the proposed metrics to bodies within our Solar System for comparison reveals two planets in the Gliese 581 system, GJ 581 c and d, with an ESI comparable to that of Mars and a PHI between that of Europa and Enceladus. 相似文献
844.
S A Liebman R A Pesce-Rodriguez C N Matthews 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1995,15(3):71-80
Hydrogen cyanide polymerizes readily to a black solid from which a yellow-brown powder can be extracted by water and further hydrolyzed to alpha-amino acids. These macromolecules could be major components of the dark matter observed on many bodies in the outer solar system, including comets and asteroids. Primitive Earth might therefore have been covered with HCN polymers through bolide bombardment or be terrestrial synthesis. Several instrumental methods were used for the separation and identification of these intriguing polymeric materials, including photoacoustic Fourier transform infrared spectroscopy, supercritical fluid extraction chromatography and pyrolysis mass spectrometry. Our integrated analytical approach revealed fragmentation patterns and chemical functionalities consistent with the presence of polymeric peptide precursors both in HCN polymers and in the Murchison meteorite. 相似文献
845.
846.
V. N. Oraevsky Yu. Ya. Ruzhin Kh. D. Kanonidi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(12):147-150
Here are presented experimental results concerning the registration by ground magnetometers of artificial MHD echo generated by powerful pulse current in ground loop contour. Data analysis was made of several magnetic stations for 16 experiments with giant loop-current contour giving magnetic flux 106nT/km2 (the current attained 20 kA). Only several rather weak bursts were registered which appeared 78±2s after main switch impulse. Echo signal was a few nanotesla. Taking into account real magnetosphere tube configuration for L ≈ 5,5 and Kp≤2 it was shown that the signal with such a delay corresponds to propagation of artificial excited Alfven echo, returning back from a magnetoconjugate ionospheric region. Meanwhile, the amplitude exceed by one order the theoretically calculated one. 相似文献
847.
On-board image compression systems aim to increase the amount of data stored in the on-board mass memory and transmitted to the ground station. This paper presents an overview and analysis of the state-of-the-art in on-board image compression systems. Compression methods and systems implementations are reviewed. Statistical analysis and developing trends are given. A new architecture of an on-board image compression system for future disaster monitoring multi-satellite missions in LEO is described. 相似文献
848.
The actual topic of optimization of multi-orbit low-thrust spacecraft inter-orbital transfers is considered. We have developed
an original approach to solving this problem, and it is described. 相似文献
849.
M. Hayosh Z. Nme
ek J. afrnkov G.N. Zastenker 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2005,36(12):2417-2422
The magnetosheath plays a dominant role in the Sun–Earth connection because the magnetosheath field and plasma actually interact with the magnetosphere. The interactions change the magnetospheric magnetic field from its nominal value through a long chain of different processes. The change is usually described by geomagnetic indices and thus it can be expected that these indices would reflect changes in the magnetosheath. The present paper analyzes the relation between geomagnetic activity characterized by changes of the Kp, DST and AE indices and ion flux measured in the night-side magnetosheath. The results suggest a weak dependence of the DST index on the ion flux in the inner magnetosheath that is connected with a magnetopause displacement. On the other hand, fluctuations of the ion flux in the analyzed frequency range do not correlate with any of the indices. 相似文献
850.
This article proposes a short review of our present knowledge of solar system magnetospheres, with the purpose of placing
the study of Saturn’s magnetosphere in the context of a comparative approach. We describe the diversity of solar system magnetospheres
and the underlying causes of this diversity: nature and magnetization state of the planetary obstacle, presence or not of
a dense atmosphere, rotation state of the planet, existence of a system of satellites, rings and neutral gas populations in
orbit around the planet. We follow the “russian doll” hierarchy of solar system magnetospheres to briefly describe the different
objects of this family: the heliosphere, which is the Sun’s magnetosphere; the “elementary” magnetospheres of the inner planets,
Earth and Mercury; the “complex” magnetospheres of the giant planets, dominated by planetary rotation and the presence of
interacting objects within their magnetospheric cavities, some of which, like Ganymede, Io or Titan, produce small intrinsic
or induced magnetospheres inside the large one.We finally describe the main original features of Saturn’s magnetosphere as
we see them after the Voyager fly-bys and before the arrival of Cassini at Saturn, and list some of the key questions which
Cassini will have to address during its four-year orbital tour. 相似文献