Extremophiles and the search for extraterrestrial life

Extremophiles thrive in ice, boiling water, acid, the water core of nuclear reactors, salt crystals, and toxic waste and in a range of other extreme habitats that were previously thought to be inhospitable for life. Extremophiles include representatives of all three domains (Bacteria, Archaea, and Eucarya); however, the majority are microorganisms, and a high proportion of these are Archaea. Knowledge of extremophile habitats is expanding the number and types of extraterrestrial locations that may be targeted for exploration. In addition, contemporary biological studies are being fueled by the increasing availability of genome sequences and associated functional studies of extremophiles. This is leading to the identification of new biomarkers, an accurate assessment of cellular evolution, insight into the ability of microorganisms to survive in meteorites and during periods of global extinction, and knowledge of how to process and examine environmental samples to detect viable life forms. This paper evaluates extremophiles and extreme environments in the context of astrobiology and the search for extraterrestrial life.     

Porphyrin as an ideal biomarker in the search for extraterrestrial life

A key issue in astrobiological research is identifying target molecules that are unambiguously biological in origin and can be easily detected and recognized. We suggest porphyrin derivatives as an ideal target, because these chromophores are global in distribution and found in virtually all living organisms on Earth, including microorganisms that may approximate the early evolution of life on Earth. We discuss the inherent qualities that make porphyrin ideally suited for astrobiological research and discuss methods for detecting porphyrin molecules in terrestrial sedimentary environments. We present preliminary data to support the use of ToFSIMS as a powerful technique in the identification of porphyrins.     

A non-earthcentric approach to life detection

The ultimate goal of a comprehensive life detection strategy is never to miss life when we encounter it. To accomplish this goal, we must define life in universal, that is, non-Earthcentric, measurable terms. Next, we must understand the nature of biosignatures observed from the measured parameters of life. And finally, we must have a clear idea of the end-member states for the search--what does life, past life, or no life look like (in terms of the measured parameters) at multiple spatial and temporal scales? If we can approach these problems both in the laboratory and in the field on Earth, then we have a chance of being able to detect life elsewhere in our solar system. What are the required limits of detection at each of those scales? What spatial, spectral, and temporal resolutions are necessary to detect life? These questions are actively being investigated in our group, and in this report, we present our strategy and approach to non-Earthcentric life detection.     

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.     

Possibilities for the detection of microbial life on extrasolar planets

We consider possibilities for the remote detection of microbial life on extrasolar planets. The Darwin/Terrestrial Planet Finder (TPF) telescope concepts for observations of terrestrial planets focus on indirect searches for life through the detection of atmospheric gases related to life processes. Direct detection of extraterrestrial life may also be possible through well-designed searches for microbial life forms. Satellites in Earth orbit routinely monitor colonies of terrestrial algae in oceans and lakes by analysis of reflected ocean light in the visible region of the spectrum. These remote sensing techniques suggest strategies for extrasolar searches for signatures of chlorophylls and related photosynthetic compounds associated with life. However, identification of such life-related compounds on extrasolar planets would require observations through strong, interfering absorptions and scattering radiances from the remote atmospheres and landmasses. Techniques for removal of interfering radiances have been extensively developed for remote sensing from Earth orbit. Comparable techniques would have to be developed for extrasolar planet observations also, but doing so would be challenging for a remote planet. Darwin/TPF coronagraph concepts operating in the visible seem to be best suited for searches for extrasolar microbial life forms with instruments that can be projected for the 2010-2020 decades, although resolution and signal-to-noise ratio constraints severely limit detection possibilities on terrestrial-type planets. The generation of telescopes with large apertures and extremely high spatial resolutions that will follow Darwin/TPF could offer striking possibilities for the direct detection of extrasolar microbial life.     

Reactions to receipt of a message from extraterrestrial intelligence: a cross-cultural empirical study

If we ever receive a message from extraterrestrial intelligence (ETI), the societal impact may be significant. To date, several authors have speculated on factors that may predict people’s reactions, but there have been no systematic empirical studies on the range of responses. One obstacle to conducting such studies is that there has been no questionnaire to assess such reactions. In the current study we have designed a psychometrically sound set of scales to assess six beliefs: (1) that extraterrestrial life exists, (2) that ETI would be benevolent and that we should respond to a message, (3) that ETI would be malevolent, (4) that message receipt would be unsettling, (5) that message receipt would be religiously significant and (6) that experts should determine the content of a reply. We report on the construction and use of these new scales, drawing on data gathered from American and Chinese undergraduate students. Respondents also completed measures of alienation, optimism, anthropocentrism and religiosity. This allowed us to predict beliefs about ETI based on personal characteristics and beliefs of the respondents.     

基于AMESim的冲压发动机燃油调节器动态特性仿真

基于AMESim软件仿真平台,建立了冲压发动机燃油调节器仿真模型,对燃油调节器的流量跟随调节特性、入口压力扰动以及油路切换过程的动态特性进行了仿真研究,分析各工况下燃油调节器的稳定性,并提出了改善燃油调节器动态特性的措施。另外,通过利用该仿真模型,对燃油调节器的各种工况进行分析,为结构参数的选取和控制参数的优化研究都提供了参考。     

The possible origin and persistence of life on Enceladus and detection of biomarkers in the plume

The jets of icy particles and water vapor issuing from the south pole of Enceladus are evidence for activity driven by some geophysical energy source. The vapor has also been shown to contain simple organic compounds, and the south polar terrain is bathed in excess heat coming from below. The source of the ice and vapor, and the mechanisms that accelerate the material into space, remain obscure. However, it is possible that a liquid water environment exists beneath the south polar cap, which may be conducive to life. Several theories for the origin of life on Earth would apply to Enceladus. These are (1) origin in an organic-rich mixture, (2) origin in the redox gradient of a submarine vent, and (3) panspermia. There are three microbial ecosystems on Earth that do not rely on sunlight, oxygen, or organics produced at the surface and, thus, provide analogues for possible ecologies on Enceladus. Two of these ecosystems are found deep in volcanic rock, and the primary productivity is based on the consumption by methanogens of hydrogen produced by rock reactions with water. The third ecosystem is found deep below the surface in South Africa and is based on sulfur-reducing bacteria consuming hydrogen and sulfate, both of which are ultimately produced by radioactive decay. Methane has been detected in the plume of Enceladus and may be biological in origin. An indicator of biological origin may be the ratio of non-methane hydrocarbons to methane, which is very low (0.001) for biological sources but is higher (0.1-0.01) for nonbiological sources. Thus, Cassini's instruments may detect plausible evidence for life by analysis of hydrocarbons in the plume during close encounters.     

基于动网格技术的固体燃料冲压发动机燃面瞬态退移速率研究

为了研究固体燃料冲压发动机(SFRJ)燃面退移速率在工作过程中的变化特性,基于发动机工作特点及动网格技术,考虑到燃烧流动及燃料表面的对流、辐射换热与燃料热解退移等过程耦合的影响,建立了SFRJ燃面瞬态退移速率预示方法,并对某带补燃室、以聚乙烯(PE)为燃料的试验发动机的燃烧室-喷管统一内流场进行数值计算,得到在移动边界条件下的瞬态流场分布,并分析了内弹道参数云图及其随时间的变化规律。结果表明,燃烧主要发生在当量比函数φ在-2～2之间的区域;随着发动机工作,燃速逐渐降低,且再附点向下游移动,燃料通道出口处流速和温度有降低趋势;此外,在小型发动机工作初期,燃料通道尾部出现类似固体火箭发动机的侵蚀燃烧现象。研究表明,该方法能成功求解发动机复杂的非定常工作过程,较好揭示燃面退移过程。所得结论对发动机设计和试验具有一定指导意义。     

Extremophiles may be irrelevant to the origin of life

In recent years, Bacteria and Archaea have been discovered living in practically every conceivable terrestrial environment, including some previously thought to be too extreme for survival. Exploration of our solar system has revealed a number of extraterrestrial bodies that harbor environments analogous to many of the terrestrial environments in which extremophiles flourish. The recent discovery of more than 105 extrasolar planets suggests that planetary systems are quite common. These three findings have led some to speculate that life is therefore common in the universe, as life as we know it can seemingly survive almost anywhere there is liquid water. It is suggested here that while environments capable of supporting life may be common, this does not in itself support the notion that life is common in the universe. Given that interplanetary transfer of life may be unlikely, the actual origin of life may require specific environmental and geological conditions that may be much less common than the mere existence of liquid water.     

Rock surfaces as life indicators: new ways to demonstrate life and traces of former life

Life and its former traces can only be detected from space when they are abundant and exposed to the planetary atmosphere at the moment of investigation by orbiters. Exposed rock surfaces present a multifractal labyrinth of niches for microbial life. Based upon our studies of highly stress-resistant microcolonial fungi of stone monument and desert rock surfaces, we propose that microbial biofilms that develop and become preserved on rock surfaces can be identified remotely by the following characteristics: (1) the existence of spectroscopically identifiable compounds that display unique adsorption, diffraction, and reflection patterns characteristic of biogenerated organic compounds (e.g., chlorophylls, carotenes, melanins, and possibly mycosporines), (2) demonstrably biogenic geomorphological features (e.g., biopitting, biochipping, and bioexfoliation), and (3) biominerals produced in association with biofilms that occupy rock surfaces (e.g., oxalates, forsterite, and special types of carbonates, sulfides, and silicates). Such traces or biosignatures of former life could provide macroscopically visible morphotypes and chemically identifiable products uniquely indicative of life.     

Experimental investigation of fuel regression rate in a HTPB based lab-scale hybrid rocket motor

The fuel regression rate is an important parameter in the design process of the hybrid rocket motor. Additives in the solid fuel may have influences on the fuel regression rate, which will affect the internal ballistics of the motor. A series of firing experiments have been conducted on lab-scale hybrid rocket motors with 98% hydrogen peroxide (H₂O₂) oxidizer and hydroxyl terminated polybutadiene (HTPB) based fuels in this paper. An innovative fuel regression rate analysis method is established to diminish the errors caused by start and tailing stages in a short time firing test. The effects of the metal Mg, Al, aromatic hydrocarbon anthracene (C₁₄H₁₀), and carbon black (C) on the fuel regression rate are investigated. The fuel regression rate formulas of different fuel components are fitted according to the experiment data. The results indicate that the influence of C₁₄H₁₀ on the fuel regression rate of HTPB is not evident. However, the metal additives in the HTPB fuel can increase the fuel regression rate significantly.     

伪谱法在飞行器轨迹优化中应用分析

伪谱法作为一种在飞行器轨迹优化领域广泛应用的方法,国内外缺乏对其进行综合研究分析的相关文献。介绍了伪谱法在飞行器轨迹优化领域的发展现状,详细分析了已应用于飞行器轨迹优化的4种伪谱法的特点和应用情况,总结了这4种方法优缺点:Legendre伪谱法研究较早、应用最为广泛,Gauss伪谱法和Radau伪谱法精度较高,而Chebyshev伪谱法理论上精度高但研究刚起步。伪谱法具有全局特性,计算精度高,收敛快,但也存在缺乏收敛解判定准则、难以处理非光滑问题等不足。介绍了伪谱法在处理bang-bang控制问题时所遇到的困难,对伪谱法的改进工作做出总结:改进算法,研究与其他算法相结合的优化方法。总体而言,伪谱法在轨迹优化问题上的应用前景很广。     

基于PDM的产品全寿命周期设计研究

产品数据管理作为全寿命周期设计的使能技术,可以实现产品信息和产品过程信息的统一管理,有效地加快产品开发。分析了全寿命周期设计的关键技术,将为产品全寿命周期设计技术的应用提供有益的借鉴。     

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.     

Property rights and the duty to extend human life

This article examines what the author calls the ‘argument from duty’, i.e. the argument that we should recognize private property rights in space because doing so will help us to act upon our duty to ensure the future survival of humanity. More strongly, the motivational impact of recognizing such rights may be required if we are to act upon this duty in an effective manner. The article argues that the duty in question is important but not overriding and that there are other duties with which it may happen to conflict. More specifically, the practical requirements of human resettlement may conflict with our duty to pursue a more just and environmentally sensitive way of living here on Earth. If this is correct, only a significantly weakened argument from duty may be made. The article also strengthens the case for thinking about our duties in the light of other ethical considerations.     

基于被动探测的目标磁扰动信号检测与定位

针对目标探测定位的快速发展中,军事领域主动雷达存在的缺陷和实现具有高度隐蔽性的目标检测技术的需求,提出一种基于被动磁矢量测量的目标扰动信号检测与定位技术.该方法利用磁传感器阵列测量目标产生的磁矢量扰动信息,通过滤波、门限检测、基函数展开等技术将有效扰动从复杂的背景场中提取出来,并结合速度估计、磁梯度张量矩阵算法研究任意...     

基于超声红外热成像技术的复合材料损伤检测

采用超声红外热成像技术,对某飞行器的复合材料壳体损伤进行了检测研究.采用数值分析模拟了超声激励下复合材料损伤处的摩擦生热及热传导过程,分析了裂纹处的温度分布及裂纹尺寸对检测结果的影响;利用超声波发生器对含分层损伤复合材料试件进行了试验,根据表面温度的分布实现了对损伤的定量识别.结果表明,超声红外热成像技术能够快速准确地检测到复合材料表面及浅表面的界面贴合型损伤(如分层,疲劳裂纹等);对损伤的定位准确、检测结果直观、不存在加热非均匀等问题;选择恰当的耦合材料能有效消除“驻波”现象的产生,并提高损伤检测效果.