The properties of alamethicin incorporated into planar lipid bilayers under the influence of microgravity.

During evolution, life on earth had adapted to the gravity of 1g. Due to space flight, in the last decades the question arose what happens to the brain under microgravity on the molecular level. Ion channels among others are the molecular basis of brain function. Therefore, the investigation of ion channel function under microgravity seems to be a promising approach to gather knowledge on brain function during space flight. In a first step, the ion channel forming peptide Alamethicin was used as a model channel in an artificial membrane. It is well suitable for this kind of investigation, since its properties are well described under standard gravity. For that reason, changes due to microgravity can be detected easily. All experiments were performed in the German drop tower at ZARM-FAB, Bremen. A special set-up was constructed based on the bilayer technique introduced by Mueller and Rudin. All functions of this set-up can be observed and controlled remotely. In the first set of experiments, a dramatic change of electrical properties of Alamethicin under microgravity could be observed. Mainly, the pore frequency is significantly reduced.     

Testing the potential for computational chemistry to quantify biophysical properties of the non-proteinaceous amino acids

Although most proteins of most living organisms are constructed from the same set of 20 amino acids, all indications are that this standard alphabet represents a mere subset of what was available to life during early evolution. However, we currently lack an appropriate quantitative framework with which to test the qualitative hypotheses that have been offered to date as explanations for nature's "choices." Specifically, although many indices have been developed to describe the 20 standard amino acids, few or no comparable data extend to prebiotically plausible alternatives because of the costly and time-consuming bench experiments that would be required. Computational chemistry (specifically quantitative structure property relationship methods) offers a potentially fast, cost-effective remedy for this knowledge gap by predicting such molecular properties in silico. Thus, we investigated the use of various freely accessible programs to predict three key amino acid properties (hydrophobicity, charge, and size). We assessed the accuracy of these predictions by comparisons with experimentally determined counterparts for appropriate test data sets. In light of these results, and factors of software accessibility and transparency, we suggest a method for further computational assessments of prebiotically plausible amino acids. The results serve as a starting point for future quantitative analysis of amino acid alphabet evolution.     

Tides and the evolution of planetary habitability

Tides raised on a planet by the gravity of its host star can reduce the planet's orbital semi-major axis and eccentricity. This effect is only relevant for planets orbiting very close to their host stars. The habitable zones of low-mass stars are also close in, and tides can alter the orbits of planets in these locations. We calculate the tidal evolution of hypothetical terrestrial planets around low-mass stars and show that tides can evolve planets past the inner edge of the habitable zone, sometimes in less than 1 billion years. This migration requires large eccentricities (>0.5) and low-mass stars ( less or similar to 0.35 M(circle)). Such migration may have important implications for the evolution of the atmosphere, internal heating, and the Gaia hypothesis. Similarly, a planet that is detected interior to the habitable zone could have been habitable in the past. We consider the past habitability of the recently discovered, approximately 5 M(circle) planet, Gliese 581 c. We find that it could have been habitable for reasonable choices of orbital and physical properties as recently as 2 Gyr ago. However, when constraints derived from the additional companions are included, most parameter choices that indicate past habitability require the two inner planets of the system to have crossed their mutual 3:1 mean motion resonance. As this crossing would likely have resulted in resonance capture, which is not observed, we conclude that Gl 581 c was probably never habitable.     

Terrestrial biological evolution and its implication for SETI

A frequent opinion among biologists upholds that biological evolution is contingent and, consequently, that man's apparition is a random event of very small probability. We present various arguments against this view, based on chemistry, molecular biology, evolutionary convergences, the existence of physical constraints on the structure of living beings, and the evidence of acceleration in the evolution of many features, e.g. brain size, over geological times. Taken together they suggest that “laws” of evolution exist and may have a universal validity. We extend this view to the evolution of “intelligence”. We show that it is an essential aspect of biological evolution and that human cultural evolution is just another aspect of it. Finally, we argue that brains more complex than the human brain are conceivable, endowed not merely with quantitatively better functions but with qualitatively higher cognitive abilities, of the kind found in the transition from, say, dog to man. This thesis predicts that the usual concept of advanced civilizations merely separated by huge distances is too restrictive. It favours a different concept, in which the separation results predominantly from cognitive, i.e. temporal factors. This idea, far from being discouraging, offers a stimulating solution to Fermi's paradox and opens new ways to SETI.     

Spatial Metaphors of Web Use

When the web became popular, people had to develop ways to talk and think about it. In the mid-1990s, we analyzed spatial language in “web talk.” We found that people described pages as places, and search as motion, both passive and active motion. Here we investigate web talk nearly two decades later. Our analysis reveals that some spatial language has stayed the same, and some has changed. Of special interest is how far fewer motion verbs are used nowadays. We argue that people naturally produce spatial metaphors when talking about new technological domains, and that over time, the most useful elements persist.     

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.     

Application of existing launch and flight system hardware for early SEI mission

A major paradigm shift in space exploration is at hand. While great discipline must be exercised, we can reinstitute the exploration of the Moon and Mars through use of current systems and technology. These early initiatives will require coupling available or growth boosters with evolving upper stages and spacecraft that employ new emerging technologies and subsystems to characterize the resources, topography, gravity and sites for future manned expeditions. We have the opportunity to perform first-rate scientific research while also serving the needs of the unfolding Space Exploration Initiative. These early programs can be pursued within limited budgets if management techniques, best described as “fast track”, are applied. Examples of such efforts that met all federal regulations, yet achieved significant returns in 1- to 2-year spans, are given.     

SETI target selection

The NASA High Resolution Microwave Survey consists of two complementary elements: a Sky Survey of the entire sky to a moderate level of sensitivity; and a Targeted Search of nearby stars, one at a time, to a much deeper level of sensitivity. In this paper we propose strategies for target selection. We have two goals: to improve the chances of successful detection of signals from technical civilizations that inhabit planets around solar-type stars, and to minimize the chances of missing signals from unexpected sites. For the main Targeted Search survey of approximately 1000 nearby solar-type stars, we argue that the selection criteria should be heavily biased by what we know about the origin and evolution of life here on Earth. We propose that observations of stars with stellar companions orbiting near the habitable zone should be de-emphasized, because such companions would prevent the formation of habitable planets. We also propose that observations of stars younger than about three billion years should be de-emphasized in favor of older stars, because our own technical civilization took longer than three billion years to evolve here on Earth. To provide the information needed for the preparation of specific target lists, we have undertaken an inventory of a large sample of solar-type stars out to a distance of 60 pc, with the goal of characterizing the relevant astrophysical properties of these stars, especially their ages and companionship. To complement the main survey, we propose that a modest sample of the nearest stars should be observed without any selection biases whatsoever. Finally, we argue that efforts to identify stars with planetary systems should be expanded. If found, such systems should receive intensive scrutiny.     

空间重离子辐照效应评述

文章对生物、半导体、光学材料、金属、聚合物的空间重离子辐照效应的研究工作进行了评述,也阐明了深入开展重离子空间环境模型以及重离子辐照效应与演化规律的研究具有重要意义。研究表明空间环境中重离子的含量虽少,但由于其高的电离能力和穿透力,对生物、半导体、光学材料、金属、聚合物等会产生各种辐射损伤效应,导致卫星信号故障、光学器件失效、金属与聚合物性能及形貌改变,甚至影响航天员的生命安全。     

Can identification of a fourth domain of life be made from sequence data alone, and could it be done on Mars?

A central question in astrobiology is whether life exists elsewhere in the universe. If so, is it related to Earth life? Technologies exist that enable identification of DNA- or RNA-based microbial life directly from environmental samples here on Earth. Such technologies could, in principle, be applied to the search for life elsewhere; indeed, efforts are underway to initiate such a search. However, surveying for nucleic acid-based life on other planets, if attempted, must be carried out with caution, owing to the risk of contamination by Earth-based life. Here we argue that the null hypothesis must be that any DNA discovered and sequenced from samples taken elsewhere in the universe are Earth-based contaminants. Experience from studies of low-biomass ancient DNA demonstrates that some results, by their very nature, will not enable complete rejection of the null hypothesis. In terms of eliminating contamination as an explanation of the data, there may be value in identification of sequences that lie outside the known diversity of the three domains of life. We therefore have examined whether a fourth domain could be readily identified from environmental DNA sequence data alone. We concluded that, even on Earth, this would be far from trivial, and we illustrate this point by way of examples drawn from the literature. Overall, our conclusions do not bode well for planned PCR-based surveys for life on Mars, and we argue that other independent biosignatures will be essential in corroborating any claims for the presence of life based on nucleic acid sequences.     

Physical–chemical properties of plasma membrane and function of erythrocytes of cosmonauts after long-term space flight

We studied microfluidity and selective ion permeability of plasma membranes and O₂-binding properties of erythrocytes of cosmonauts during early rehabilitation after a long-term space flight (LTSF). Microfluidity of plasma membranes in surface regions was found to undergo a reversible decrease during 13–15 days following LTSF, which was accompanied by a reversible increase in relative cholesterol content. Cosmonauts’ erythrocytes revealed an increased activity of Na/H-exchanger and K_Ca-channel as well as a decrease in number of discocytes and increase in number of echinocytes, stomatocytes and knizocytes. Total hemoglobin content as well as oxyhemoglobin content were lowered after the LTSF, while the affinity of hemoglobin to O₂ was advanced. It is suggested that the changes in Hb properties, microfluidity and selective permeability of plasma membranes following the elevated cholesterol content in the membranes can decrease tissue supply with O₂.     

Active polar gullies on Mars and the role of carbon dioxide

The detection of geologically recent channels and gullies on Mars has been interpreted as evidence for recent water activity on this arid and cold planet. The presence of active water would have considerable implications for the history of Mars and for the potential for an active near-surface biota; however, water is not the only substance that can flow and may actually be one of the least likely candidates when the modern permafrost environment is considered. Here, a key site of recent gully and channel development on Mars is reported at 71 degrees S in Sisyphi Cavi, within the annual zone of polar CO2 ice and snow accumulation. Superposition of channel features over and/or through the defrosting CO2 snowpack shows that the channels are active at the present day and probably have fluid flows every spring during the annual defrosting. In itself, this is a significant observation as active fluid flows of any nature have not yet been proven on Mars. However, the ambient temperature at the time of gully activity appears to require a role for CO2 in the formation of the channels, rather than water. A model is proposed for gas-lubricated flow in the channels based on avalanching of CO2 snowpack and clastic debris. If similar mechanisms are responsible for all the recent gullies on Mars, then perhaps no near-surface astrobiological targets are available.     

From suborbital space tourism to commercial personal spaceflight

Excellent essays have been recently published on the profitability and the future of space tourism. This paper is intended to supplement the considerations in this field and emphasizes the further potential evolution of commercial personal spaceflights. Indeed, based upon work done at the International Space University (ISU) the oligopolistic character of suborbital space tourism has been linked to marketing and product life cycle (PLC) considerations and has led to the thesis that space tourism as a profitable sector will require a follow-on strategy. Orbital space tourism, on one hand, could become an extension of the PLC but, on the other hand, it is assumed that point-to-point (P2P) commercial space transport will become the long term sustainable market. Without ignoring technical challenges, this paper will mainly concentrate on marketing and commercial aspects of personal spaceflight.     

A combinatorial approach to biochemical space: description and application to the redox distribution of metabolism

Redox chemistry is central to life on Earth. It is well known that life uses redox chemistry to capture energy from environmental chemical energy gradients. Here, we propose that a second use of redox chemistry, related to building biomass from environmental carbon, is equally important to life. We apply a method based on chemical structure to evaluate the redox range of different groups of terrestrial biochemicals, and find that they are consistently of intermediate redox range. We hypothesize the common intermediate range is related to the chemical space required for the selection of a consistent set of metabolites. We apply a computational method to show that the redox range of the chemical space shows the same restricted redox range as the biochemicals that are selected from that space. By contrast, the carbon from which life is composed is available in the environment only as fully oxidized or reduced species. We therefore argue that redox chemistry is essential to life for assembling biochemicals for biomass building. This biomass-building reason for life to require redox chemistry is in addition (and in contrast) to life's use of redox chemistry to capture energy. Life's use of redox chemistry for biomass capture will generate chemical by-products-that is, biosignature gases-that are not in redox equilibrium with life's environment. These potential biosignature gases may differ from energy-capture redox biosignatures.     

On a lunar space elevator

We consider a space elevator system for lunar surface access that consists of a space station in circumlunar orbit, a cable reaching down to some meters above the surface and a magnetically levitated vehicle driven by a linear motor. It accelerates the load to be lifted to the speed of the cable end. Loads to be delivered are either put on the vehicle and slowed down by it or they are slowed down by a sand braking technique in a mare terrain. It is technically possible to operate this transport system nearly without fuel supply from Earth. We calculate various steel cable dimensions for a static stress maximum of $\text{1}\text{5}\text{th}$ of the tensile strength. The process of takeover is considered in detail. Five ways of eliminating the adverse large cable elongation due to the load are described. The touchdown process and behaviour of the cable after disconnection are analysed. The positive difference between the speed of the load at takeover and cable end can excite a large inplane swing motion. We propose to damp it by a dissipative pulley that hangs in a loop of wire leading to the ends of two beams mounted on the space station tangentially to the orbit, the pulley's core being connected with the load. Roll librations are damped by energy losses in the elastic beams; damping can be reinforced by viscous beam elements and/or controlled out-of-plane motions of the beams. We argue in favour of the possibility of fast deployment. The problems of vehicle vibrations and agglutination at sand braking blades are underlined and their combined experimental investigation is suggested.     

Role of the ionosphere for the atmospheric evolution of planets

We have synthesized current understanding, mainly observations, with regard to ion escape mechanisms to space from the ionosphere and exosphere of Titan and Earth-type planets, with the intent to provide an improved input for models of atmospheric evolution on early Earth and Earth-type planets and exoplanets. We focus on the role of the ionosphere and its non-linear response to solar parameters, all of which have been underestimated in current models of ancient atmospheric escape (4 billion years ago). Factors that have been overlooked include the following: (1) Much larger variation of O(+) outflow than H(+) outflow from the terrestrial ionosphere, depending on solar and geomagnetic activities (an important consideration when attempting to determine the oxidized state of the atmosphere of early Earth); (2) magnetization of the ionopause, which keeps ionospheric ions from escaping and controls many other escape processes; (3) extra ionization by, for example, the critical ionization velocity mechanism, which expands the ionosphere to greater altitudes than current models predict; and (4) the large escape of cold ions from the dense, expanded ionosphere of Titan. Here we offer, as a guideline for quantitative simulations, a qualitative diagnosis of increases or decreases of non-thermal escape related to the ionosphere for magnetized and unmagnetized planets in response to changes in solar parameters (i.e., solar EUV/FUV flux, solar wind dynamic pressure, and interplanetary magnetic field).     

Discrimination of aqueous and aeolian paleoenvironments by atomic force microscopy-- a database for the characterization of martian sediments

In the search for aqueous habitats on Mars direct proof of (ancient) flowing water is still lacking, although remote sensing has provided indications of young fluvial systems. To demonstrate that such proof can be given, we examined surface marks on recent terrestrial sand grains by atomic force microscopy (AFM) and applied a quantitative three-dimensional analysis that can numerically distinguish between aeolian and aquatic transport mechanisms in sedimentary deposits on Earth. The surfaces of natural quartz grains as well as olivine, feldspar pyroxene, and monazite sands of known origin were imaged, each image yielding a three-dimensional map of the mineral surface. A fully automated analysis of distribution patterns of the structural elements that constitute the grain surfaces shows that wind-transported quartz grains have short linear elements irregularly distributed on the surface. Linear elements on water-transported grains, however, are longer with orientations that reflect the mineral symmetry. Because the surface patterns found on aqueous grains are due to preferential etching, they can be used as diagnostic fingerprints for the existence of past or present aqueous transport systems. We used a cluster analysis of the cross-correlation distance of distribution patterns in the structures of aeolian and aquatic sand grains to build a phenogram that provides a map for the relationship of the various sediments found on earth. The analysis shows that the method is highly significant and that water and wind transport can clearly be differentiated. In particular, feldspar and olivine sands contributed even more to the discrimination than quartz grains, which indicated that the method is promising for its application on future missions to Mars. Assuming that martian aqueous sand grains exhibit similar erosional patterns to mineral grains on Earth, simple AFM experiments on a Mars lander would be capable of proving the activity of flowing water in modern runoff systems and of analyzing the paleoenvironments of Mars.     

Earth observations: the view from the ground

A ground-level view of Earth observations reveals that emerging ground segments are of at least two major categories: those that are satellite-driven and which have top-down organizations and those that are data-driven and organized from the bottom up. Or put differently, the former are generally data users. A ground-level perspective also suggests that continually rising scientific and economic value of data and decreasing national budgets require balancing satellite investment with effective ground segment evolution to provide demonstrable reasons to continue funding both satellites and ground activities.     

八作动器隔振平台的通道耦合分析及解耦控制

分析一种对称结构的八作动器隔振平台的通道耦合特性。分析表明由于结构对称，当有效载荷质心位于平台纵轴的延长线上，且有效载荷的惯性主轴与平台对称轴平行时，平台可分解成两个独立的单自由度系统和两个2阶耦合子系统。利用矩阵同时对角化方法对平台的2阶耦合子系统进一步解耦，仿真结果显示解耦控制能够衰减被动隔振的谐振峰，改进平台的隔振性能。     

A lunar-based spacecraft propulsion concept—The ion beam sail

We describe a concept for spacecraft propulsion by means of an energetic ion beam, with the ion source fixed at the spacecraft starting point (e.g., a lunar-based ion beam generator) and not onboard the vessel. This approach avoids the substantial mass penalty associated with the onboard ion source and power supply hardware, and vastly more energetic ion beam systems can be entertained. We estimate the ion beam parameters required for various scenarios and consider some of the constraints limiting the concept. We find that the “ion beam sail” approach can be viable and attractive for journey distances not too great, for example, within the Earth–Moon system, and could potentially provide support for journeys to the inner planets.