Impact disruption and recovery of the deep subsurface biosphere

Although a large fraction of the world's biomass resides in the subsurface, there has been no study of the effects of catastrophic disturbance on the deep biosphere and the rate of its subsequent recovery. We carried out an investigation of the microbiology of a 1.76 km drill core obtained from the ～35 million-year-old Chesapeake Bay impact structure, USA, with robust contamination control. Microbial enumerations displayed a logarithmic downward decline, but the different gradient, when compared to previously studied sites, and the scatter of the data are consistent with a microbiota influenced by the geological disturbances caused by the impact. Microbial abundance is low in buried crater-fill, ocean-resurge, and avalanche deposits despite the presence of redox couples for growth. Coupled with the low hydraulic conductivity, the data suggest the microbial community has not yet recovered from the impact ～35 million years ago. Microbial enumerations, molecular analysis of microbial enrichment cultures, and geochemical analysis showed recolonization of a deep region of impact-fractured rock that was heated to above the upper temperature limit for life at the time of impact. These results show how, by fracturing subsurface rocks, impacts can extend the depth of the biosphere. This phenomenon would have provided deep refugia for life on the more heavily bombarded early Earth, and it shows that the deeply fractured regions of impact craters are promising targets to study the past and present habitability of Mars.     

Survival and germinability of Bacillus subtilis spores exposed to simulated Mars solar radiation: implications for life detection and planetary protection

Bacterial spores have been considered as microbial life that could survive interplanetary transport by natural impact processes or human spaceflight activity. Deposition of terrestrial microbes or their biosignature molecules onto the surface of Mars could negatively impact life detection experiments and planetary protection measures. Simulated Mars solar radiation, particularly the ultraviolet component, has been shown to reduce spore viability, but its effect on spore germination and resulting production of biosignature molecules has not been explored. We examined the survival and germinability of Bacillus subtilis spores exposed to simulated martian conditions that include solar radiation. Spores of B. subtilis that contain luciferase resulting from expression of an sspB-luxAB gene fusion were deposited on aluminum coupons to simulate deposition on spacecraft surfaces and exposed to simulated Mars atmosphere and solar radiation. The equivalent of 42 min of simulated Mars solar radiation exposure reduced spore viability by nearly 3 logs, while germination-induced bioluminescence, a measure of germination metabolism, was reduced by less than 1 log. The data indicate that spores can retain the potential to initiate germination-associated metabolic processes and produce biological signature molecules after being rendered nonviable by exposure to Mars solar radiation.     

Bacillus subtilis spore survival and expression of germination-induced bioluminescence after prolonged incubation under simulated Mars atmospheric pressure and composition: implications for planetary protection and lithopanspermia

Bacterial endospores in the genus Bacillus are considered good models for studying interplanetary transfer of microbes by natural or human processes. Although spore survival during transfer itself has been the subject of considerable study, the fate of spores in extraterrestrial environments has received less attention. In this report we subjected spores of a strain of Bacillus subtilis, containing luciferase resulting from expression of an sspB-luxAB gene fusion, to simulated martian atmospheric pressure (7-18 mbar) and composition (100% CO(2)) for up to 19 days in a Mars simulation chamber. We report here that survival was similar between spores exposed to Earth conditions and spores exposed up to 19 days to simulated martian conditions. However, germination-induced bioluminescence was lower in spores exposed to simulated martian atmosphere, which suggests sublethal impairment of some endogenous spore germination processes.     

探索是开发和利用空间之母

航天活动包括探索、开发和利用三个层次。文章从4个方面论述探索在整个航天活动中的作用和地位,认为探索是开发和利用之母,是航天国际化的主要途径,是航天软实力的重要体现,是发挥我负责任大国作用的展示;最后建议中国要加强探索类航天项目和航天活动的开展。     

Life at the wedge: the activity and diversity of arctic ice wedge microbial communities

The discovery of polygonal terrain on Mars underlain by ice heightens interest in the possibility that this water-bearing habitat may be, or may have been, a suitable habitat for extant life. The possibility is supported by the recurring detection of terrestrial microorganisms in subsurface ice environments, such as ice wedges found beneath tundra polygon features. A characterization of the microbial community of ice wedges from the high Arctic was performed to determine whether this ice environment can sustain actively respiring microorganisms and to assess the ecology of this extreme niche. We found that ice wedge samples contained a relatively abundant number of culturable cells compared to other ice habitats (～10(5) CFU·mL(-1)). Respiration assays in which radio-labeled acetate and in situ measurement of CO(2) flux were used suggested low levels of microbial activity, though more sensitive techniques are required to confirm these findings. Based on 16S rRNA gene pyrosequencing, bacterial and archaeal ice wedge communities appeared to reflect surrounding soil communities. Two Pseudomonas sp. were the most abundant taxa in the ice wedge bacterial library (～50%), while taxa related to ammonia-oxidizing Thaumarchaeota occupied 90% of the archaeal library. The tolerance of a variety of isolates to salinity and temperature revealed characteristics of a psychrotolerant, halotolerant community. Our findings support the hypothesis that ice wedges are capable of sustaining a diverse, plausibly active microbial community. As such, ice wedges, compared to other forms of less habitable ground ice, could serve as a reservoir for life on permanently cold, water-scarce, ice-rich extraterrestrial bodies and are therefore of interest to astrobiologists and ecologists alike. .     

Prebiotic significance of extraterrestrial ice photochemistry: detection of hydantoin in organic residues

The delivery of extraterrestrial organic materials to primitive Earth from meteorites or micrometeorites has long been postulated to be one of the origins of the prebiotic molecules involved in the subsequent apparition of life. Here, we report on experiments in which vacuum UV photo-irradiation of interstellar/circumstellar ice analogues containing H(2)O, CH(3)OH, and NH(3) led to the production of several molecules of prebiotic interest. These were recovered at room temperature in the semi-refractory, water-soluble residues after evaporation of the ice. In particular, we detected small quantities of hydantoin (2,4-imidazolidinedione), a species suspected to play an important role in the formation of poly- and oligopeptides. In addition, hydantoin is known to form under extraterrestrial, abiotic conditions, since it has been detected, along with various other derivatives, in the soluble part of organic matter of primitive carbonaceous meteorites. This result, together with other related experiments reported recently, points to the potential importance of the photochemistry of interstellar "dirty" ices in the formation of organics in Solar System materials. Such molecules could then have been delivered to the surface of primitive Earth, as well as other telluric (exo-) planets, to help trigger first prebiotic reactions with the capacity to lead to some form of primitive biomolecular activity.     

Ultraviolet-stimulated fluorescence and phosphorescence of aromatic hydrocarbons in water ice

A principal goal of astrobiology is to detect and inventory the population of organic compounds on extraterrestrial bodies. Targets of specific interest include the wealth of icy worlds that populate our Solar System. One potential technique for in situ detection of organics trapped in water ice matrices involves ultraviolet-stimulated emission from these compounds. Here, we report a preliminary investigation into the feasibility of this concept. Specifically, fluorescence and phosphorescence of pure benzene ice and 1% mixtures of benzene, toluene, p-xylene, m-xylene, and o-xylene in water ice, respectively, were studied at temperatures ranging from ～17 K up to 160 K. Spectra were measured from 200-500 nm (50,000-20,000 cm(-1)) while ice mixtures were excited at 248.6 nm. The temperature dependence of the fluorescence and phosphorescence intensities was found to be independent of the thermal history and phase of the ice matrix in all cases examined. All phosphorescent emissions were found to decrease in intensity with increasing temperature. Similar behavior was observed for fluorescence in pure benzene, while the observed fluorescence intensity in water ices was independent of temperature.     

MERLIN: Mars-Moon Exploration,Reconnaissance and Landed Investigation

Mars' moons Phobos and Deimos are low-albedo, D-type bodies that may preserve samples of outer solar system material that contributed organics and volatiles to the accreting terrestrial planets. A Discovery-class mission concept described in this paper, the Mars-Moon Exploration, Reconnaissance and Landed Investigation (MERLIN), will obtain in situ measurements from Deimos to test models for the moon's origin. The measurement objectives of MERLIN are to determine Deimos' elemental and mineralogical composition, to investigate its volatile and organic content, and to characterize processes that have modified its surface. To achieve these objectives, a landed payload will provide stereo imaging and measurements of elemental and mineralogical composition and interior structure. An orbital payload will acquire global high-resolution and color imaging, putting the landing site in context by characterizing Deimos' geology. Following MOI the spacecraft flies in formation with Deimos, and uses small changes in its orbit around Mars to investigate Deimos from a range of altitudes and illuminations over 4 months. Data taken during 1- to 2-km altitude flyovers will certify a landing site. The spacecraft will be delivered to a point several kilometers above Deimos, and will navigate to landing on a fresh exposure of regolith using onboard imaging. 90 days of baseline landed operations will provide a complete set of measurements, with schedule reserve, and there is sufficient propellant to repeat the measurements at a second site.     

The relative stability of belligerent and peaceful societies: implications for SETI

Although initially we will know virtually nothing about any society that our microwave search detects, in all likelihood their society will be far older than ours. It will have evolved mechanisms to ensure longevity. A pessimistic hypothesis would lead us to expect a powerful, aggressive and self-serving society that has vanquished all challengers. If this hypothesis were true, a response by us to their signal could be dangerous. An optimistic hypothesis, that it is the peaceful societies that survive, would lead us to expect a benign or even friendly civilization. If this second hypothesis were true, our response would gratify their scientific curiosity and perhaps lead to a useful exchange of information. Convergent evidence from the quantitative analyses of long-term historical trends and computer modeling support the optimistic hypothesis. Although not conclusive, this analysis suggests that revealing our presence in the Universe is a low risk activity.     

大学新生入学适应教育探析

本研究以410名大学新生为被试,采用问卷法调查了入学第一个学期学生的精神健康水平,考察了他们的入学适应状况,调查结果表明:一部分学生在新环境的适应上存在较多问题.本文在调查研究的基础上,对提高大学生入学适应水平的教育途径和方法做出了尝试性的探讨.     

Spacecraft technology portfolio: Probabilistic modeling and implications for responsiveness and schedule slippage

Addressing the challenges of Responsive Space and mitigating the risk of schedule slippage in space programs require a thorough understanding of the various factors driving the development schedule of a space system. The present work contributes theoretical and practical results in this direction. A spacecraft is here conceived of as a technology portfolio. The characteristics of this portfolio are defined as its size (e.g., number of instruments), the technology maturity of each instrument and the resulting Technology Readiness Level (TRL) heterogeneity, and their effects on the delivery schedule of a spacecraft are investigated. Following a brief overview of the concept of R&D portfolio and its relevance to spacecraft design, a probabilistic model of the Time-to-Delivery of a spacecraft is formulated, which includes the development, Integration and Testing, and Shipping phases. The Mean-Time-To-Delivery (MTTD) of the spacecraft is quantified based on the portfolio characteristics, and it is shown that the Mean-Time-To-Delivery (MTTD) of the spacecraft and its schedule risk are significantly impacted by decreasing TRL and increasing portfolio size. Finally, the utility implications of varying the portfolio characteristics are investigated, and “portfolio maps” are provided as guides to help system designers identify appropriate portfolio characteristics when operating in a calendar-based design environment (which is the paradigm shift that space responsiveness introduces).     

材料腐蚀与涂装防护技术

~~材料腐蚀与涂装防护技术$中国航天科工集团西安二一0研究所@马天信$宝鸡文理学院化学系@姜波~~~~~~     

电子系统的电磁脉冲效应及防护

电磁脉冲对电子系统具有很强的干扰和破坏作用.为研究电磁脉冲对电子系统的影响,进行了静电放电电磁脉冲对单片机系统的辐照效应实验.实验表明,单片机系统在静电放电电磁脉冲作用下,会出现多种故障现象.在效应实验基础上,研究了单片机加固技术.     

大学新生入学适应教育探析

本研究以410名大学新生为被试,采用问卷法调查了入学第一个学期学生的精神健康水平,考察了他们的入学适应状况,调查结果表明：一部分学生在新环境的适应上存在较多问题。本文在调查研究的基础上,对提高大学生入学适应水平的教育途径和方法做出了尝试性的探讨。     

GPS防护及干扰监测与定位技术研究

随着GPS导航定位技术的日臻完善,其在军民领域的应用范围也越来越广,对GPS的干扰监测和抗干扰措施一直是该领域的热门研究课题。美国政府为了使GPS系统免受各种无意或人为干扰,建立了GPS保障机制,并研究部署了干扰监测定位系统。这些措施有效保障了GPS系统的正常工作,确保其国内重要基础设施和关键资源部门安全连续地稳定运行。针对GPS干扰普遍存在的问题,重点介绍了GPS保护机制的主要计划和措施,总结了GPS干扰监测定位系统的发展趋势,为导航干扰监测与定位系统的规划研究提供参考依据。     

Satellite communications and the Internet: implications for the outer space treaty

The speedily expanding Internet is in the process of transforming the technological, economic, and policy bases for nation-state regulation of telecommunications, including space-based satellite networks. Deployment of the packet-switched Internet has accelerated the liberalization of telecommunications markets and has led to far-reaching regulatory restructuring and policy shifts regarding state ownership and control of networks and information flows. As space-based GMPCS networks become integral parts of the globalizing Internet infrastructure, the state-centric legal paradigm requiring state “authorization and continuing supervision” of space activities by “non-governmental entities” stipulated under Article VI of the OST and associated treaties forming the outer space legal regime will be called increasingly into question. This paper examines the technological, economic/trade, and security issues that question whether the existing state-centric paradigm for regulating Internel-based GMPCS satellite systems will remain in legal phase with emerging liberalized regulatory regimes for terrestrial Internet-based infractructures.     

NASA's new Mars Exploration Program: the trajectory of knowledge

NASA's newly restructured Mars Exploration Program (MEP) is finally on the way to Mars with the successful April 7 launch of the 2001 Mars Odyssey Orbiter. In addition, the announcement by the Bush Administration that the exploration of Mars will be a priority within NASA's Office of Space Science further cements the first decade of the new millennium as one of the major thrusts to understand the "new" Mars. Over the course of the past year and a half, an integrated team of managers, scientists, and engineers has crafted a revamped MEP to respond to the scientific as well as management and resource challenges associated with deep space exploration of the Red Planet. This article describes the new program from the perspective of its guiding philosophies, major events, and scientific strategy. It is intended to serve as a roadmap to the next 10-15 years of Mars exploration from the NASA viewpoint. [For further details, see the Mars Exploration Program web site (URL): http://mars.jpl.nasa.gov]. The new MEP will certainly evolve in response to discoveries, to successes, and potentially to setbacks as well. However, the design of the restructured strategy is attentive to risks, and a major attempt to instill resiliency in the program has been adopted. Mars beckons, and the next decade of exploration should provide the impetus for a follow-on decade in which multiple sample returns and other major program directions are executed. Ultimately the vision to consider the first human scientific expeditions to the Red Planet will be enabled. By the end of the first decade of this program, we may know where and how to look for the elusive clues associated with a possible martian biological record, if any was every preserved, even if only as "chemical fossils."     

Archaeal genome organization and stress responses: implications for the origin and evolution of cellular life

For DNA to be used as an informational molecule it must exist in the cell on the edge of stability because all genomic processes require local controlled melting. This presents mechanistic opportunities and problems for genomic DNA from hyperthermophilic organisms, whose unpackaged DNA could melt at optimal temperatures for growth. Hyperthermophiles are suggested to employ the novel positively supercoiling topoisomerase enzyme reverse gyrase (RG) to form positively supercoiled DNA that is intrinsically resistant to thermal denaturation. RG is presently the only archaeal gene that is uniquely found in hyperthermophiles and therefore is central to hypotheses suggesting a hypothermophilic origin of life. However, the suggestion that RG has evolved by the fusion of two pre-existing enzymes has led to hypotheses for a lower temperature for the origin of life. In addition to the action of topoisomerases, DNA packaging and the intracellular ionic environment can also manipulate DNA topology significantly. In the Euryarchaeota, nucleosomes containing minimal histones can adopt two alternate DNA topologies in a salt-dependent manner. From this we hypothesize that since internal salt concentrations are increased following an increase in temperature, the genomic effects of temperature fluctuations could also be accommodated by changes in nucleosome organization. In addition, stress-induced changes in the nucleoid proteins could also play a role in maintaining the genome in the optimal topological state in changing environments. The function of these systems could therefore be central to temperature adaptation and thus be implicated in origin of life scenarios involving hyperthermophiles.     

Critical issues in connection with human planetary missions: protection of and from the environment.

Activities associated with human missions to the Moon or to Mars will interact with the environment in two reciprocal ways: (i) the mission needs to be protected from the natural environmental elements that can be harmful to human health, the equipment or to their operations: (ii) the specific natural environment of the Moon or Mars should be protected so that it retains its value for scientific and other purposes. The following environmental elements need to be considered in order to protect humans and the equipment on the planetary surface: (i) cosmic ionizing radiation, (ii) solar particle events; (iii) solar ultraviolet radiation; (iv) reduced gravity; (v) thin atmosphere; (vi) extremes in temperatures and their fluctuations; (vii) surface dust; (viii) impacts by meteorites and micrometeorites. In order to protect the planetary environment. the requirements for planetary protection as adopted by COSPAR for lander missions need to be revised in view of human presence on the planet. Landers carrying equipment for exobiological investigations require special consideration to reduce contamination by terrestrial microorganisms and organic matter to the Greatest feasible extent. Records of human activities on the planet's surface should be maintained in sufficient detail that future scientific experimenters can determine whether environmental modifications have resulted from explorations. Grant numbers: 14056/99/NL/PA.