Exoplanets: the quest for Earth twins

Today, more than 400 extra-solar planets have been discovered. They provide strong constraints on the structure and formation mechanisms of planetary systems. Despite this huge amount of data, we still have little information concerning the constraints for extra-terrestrial life, i.e. the frequency of Earth twins in the habitable zone and the distribution of their orbital eccentricities. On the other hand, these latter questions strongly excite general interest and trigger future searches for life in the Universe. The status of the extra-solar planets field--in particular with respect to very-low-mass planets--will be discussed and an outlook on the search for Earth twins will be given in this paper.     

The evolution of organic matter in space

Carbon, and molecules made from it, have already been observed in the early Universe. During cosmic time, many galaxies undergo intense periods of star formation, during which heavy elements like carbon, oxygen, nitrogen, silicon and iron are produced. Also, many complex molecules, from carbon monoxide to polycyclic aromatic hydrocarbons, are detected in these systems, like they are for our own Galaxy. Interstellar molecular clouds and circumstellar envelopes are factories of complex molecular synthesis. A surprisingly high number of molecules that are used in contemporary biochemistry on the Earth are found in the interstellar medium, planetary atmospheres and surfaces, comets, asteroids and meteorites and interplanetary dust particles. Large quantities of extra-terrestrial material were delivered via comets and asteroids to young planetary surfaces during the heavy bombardment phase. Monitoring the formation and evolution of organic matter in space is crucial in order to determine the prebiotic reservoirs available to the early Earth. It is equally important to reveal abiotic routes to prebiotic molecules in the Earth environments. Materials from both carbon sources (extra-terrestrial and endogenous) may have contributed to biochemical pathways on the Earth leading to life's origin. The research avenues discussed also guide us to extend our knowledge to other habitable worlds.     

Astrobiology, space and the future age of discovery

Astrobiology is the study of the origins, evolution, distribution and future of life in the Universe, and specifically seeks to understand the origin of life and to test the hypothesis that life exists elsewhere than on Earth. There is a general mathematics, physics and chemistry; that is, scientific laws that obtain on Earth also do so elsewhere. Is there a general biology? Is the Universe life-rich or is Earth an isolated island of biology? Exploration in the Age of Enlightenment required the collection of data in unexplored regions and the use of induction and empiricism to derive models and natural laws. The current search for extra-terrestrial life has a similar goal, but with a much greater amount of data and with computers to help with management, correlations, pattern recognition and analysis. There are 60 active space missions, many of them aiding in the search for life. There is not a universally accepted definition of life, but there are a series of characteristics that can aid in the identification of life elsewhere. The study of locations on Earth with similarities to early Mars and other space objects could provide a model that can be used in the search for extra-terrestrial life.     

Effect of vibrations on the laboratory model “earthquake” statistics

Earthquakes result from the development of a dynamic instability of the stick-slip type in a system of faults in the Earth’s crust, when the elastic energy accumulated during a long smooth motion of fragments exhibits rapid relaxation when the stresses reach a critical level. The statistics of dynamic instabilities has been studied in a model tribological system demonstrating an analogous behavior. A distribution function of the magnitude of acceleration, which arises upon slippage of a sample modeling a fragment of the Earth’s crust, covers several orders of magnitude. This is analogous to the statistics of real earthquakes obeying the Gutenberg-Richter law. The possibility of modifying the model “earthquake” statistics by means of an external vibrational action upon the system has been studied: the external action was controlled so as to decrease the probability of strong (high-acceleration) jumps at the expense of weak jumps, thus converting the displacement dynamics into a creep regime. It is established that the “earthquake” statistics in most of the tribological couples studied can be modified in a desired manner under the action of vibrations.     

Chemical methods for searching for evidence of extra-terrestrial life

This paper describes the chemical concepts used for the purpose of detecting life in extra-terrestrial situations. These methods, developed initially within the oil industry, have been used to determine when life began on Earth and for investigating the Moon and Mars via space missions. In the case of Mars, the Viking missions led to the realization that we had meteorites from Mars on Earth. The study of Martian meteorites in the laboratory provides tantalizing clues for life on Mars in both the ancient and recent past. Meteorite analyses led to the launch of the Beagle 2 spacecraft, which was designed to prove that life-detection results obtained on Earth were authentic and not confused by terrestrial contamination. Some suggestions are made for future work.     

Predicting what extra-terrestrials will be like: and preparing for the worst

It is difficult to imagine evolution in alien biospheres operating in any manner other than Darwinian. Yet, it is also widely assumed that alien life-forms will be just that: strange, un-nerving and probably repulsive. There are two reasons for this view. First, it is assumed that the range of habitable environments available to extra-terrestrial life is far wider than on Earth. I suggest, however, that terrestrial life is close to the physical and chemical limits of life anywhere. Second, it is a neo-Darwinian orthodoxy that evolution lacks predictability; imagining what extra-terrestrial life would look like in any detail is a futile exercise. To the contrary, I suggest that the outcomes of evolution are remarkably predictable. This, however, leads us to consider two opposites, both of which should make our blood run cold. The first, and actually extremely unlikely, is that alien biospheres will be strikingly similar to our terrestrial equivalent and that in such biospheres intelligence will inevitably emerge. The reasons for this revolve around the ubiquity of evolutionary convergence, the determinate structure of the Tree of Life and molecular inherency. But if something like a human is an inevitability, why do I also claim that the first possibility is 'extremely unlikely'? Simply because the other possibility is actually the correct answer. Paradoxically, we and our biosphere are completely alone. So which is worse? Meeting ourselves or meeting nobody?     

Numerical modelling of fluids mixing,heat transfer and non‐equilibrium redox chemical reactions in fluid‐saturated porous rocks

Non‐equilibrium redox chemical reactions of high orders are ubiquitous in fluid‐saturated porous rocks within the crust of the Earth. The numerical modelling of such high‐order chemical reactions becomes a challenging problem because these chemical reactions are not only produced strong non‐linear source/sink terms for reactive transport equations, but also often coupled with the fluids mixing, heat transfer and reactive mass transport processes. In order to solve this problem effectively and efficiently, it is desirable to reduce the total number of reactive transport equations with strong non‐linear source/sink terms to a minimum in a computational model. For this purpose, the concept of the chemical reaction rate invariant is used to develop a numerical procedure for dealing with fluids mixing, heat transfer and non‐equilibrium redox chemical reactions in fluid‐saturated porous rocks. Using the proposed concept and numerical procedure, only one reactive transport equation, which is used to describe the distribution of the chemical product and has a strong non‐linear source/sink term, needs to be solved for each of the non‐equilibrium redox chemical reactions. The original reactive transport equations of the chemical reactants with strong non‐linear source/sink terms are turned into the conventional mass transport equations of the chemical reaction rate invariants without any non‐linear source/sink terms. A testing example, for some aspects of which the analytical solutions are available, is used to validate the proposed numerical procedure. The related numerical solutions have demonstrated that (1) the proposed numerical procedure is useful and applicable for dealing with the coupled problem between fluids mixing, heat transfer and non‐equilibrium redox chemical reactions of high orders in fluid‐saturated porous rocks; (2) the interaction between the solute diffusion, solute advection and chemical kinetics is an important mechanism to control distribution patterns of chemical products in an ore‐forming process; and (3) if the pore‐fluid pressure gradient is lithostatic, it is difficult for the chemical equilibrium to be attained within permeable cracks and geological faults within the crust of the Earth. Copyright © 2005 John Wiley & Sons, Ltd.     

How does the Earth system generate and maintain thermodynamic disequilibrium and what does it imply for the future of the planet?

The Earth's chemical composition far from chemical equilibrium is unique in our Solar System, and this uniqueness has been attributed to the presence of widespread life on the planet. Here, I show how this notion can be quantified using non-equilibrium thermodynamics. Generating and maintaining disequilibrium in a thermodynamic variable requires the extraction of power from another thermodynamic gradient, and the second law of thermodynamics imposes fundamental limits on how much power can be extracted. With this approach and associated limits, I show that the ability of abiotic processes to generate geochemical free energy that can be used to transform the surface-atmosphere environment is strongly limited to less than 1?TW. Photosynthetic life generates more than 200?TW by performing photochemistry, thereby substantiating the notion that a geochemical composition far from equilibrium can be a sign for strong biotic activity. Present-day free energy consumption by human activity in the form of industrial activity and human appropriated net primary productivity is of the order of 50?TW and therefore constitutes a considerable term in the free energy budget of the planet. When aiming to predict the future of the planet, we first note that since global changes are closely related to this consumption of free energy, and the demands for free energy by human activity are anticipated to increase substantially in the future, the central question in the context of predicting future global change is then how human free energy demands can increase sustainably without negatively impacting the ability of the Earth system to generate free energy. This question could be evaluated with climate models, and the potential deficiencies in these models to adequately represent the thermodynamics of the Earth system are discussed. Then, I illustrate the implications of this thermodynamic perspective by discussing the forms of renewable energy and planetary engineering that would enhance the overall free energy generation and, thereby 'empower' the future of the planet.     

Materials science issues in the Earth and planetary sciences

Earth is a dynamic planet. Solid state convection in the deep interior is coupled to the motion of about a dozen rigid plates at the surface. Earthquakes, volcanoes and mountains are located mainly at the boundaries between plates and reflect the relative motion between them. The associated deformation processes span a wide range of regimes from high temperature dislocation and diffusion accommodated creep to brittle fracture, friction, fragmentation and granular flow. There is a long history of collaboration between earth and materials scientists in modeling the relevant micromechanics and formulating appropriate constitutive relations. Materials analysis in the Earth and planetary sciences pose special challenges. Pressure and temperature conditions in the Earth's interior reach 360 GPa and 8000 K so that constitutive equations must often be extended to pressure and temperature regimes well beyond laboratory limits. Deformation occurs over a range of temporal and spatial scales difficult to simulate in the laboratory. The emergence of deformation structures spanning many spatial orders of magnitude has made Earth sciences the test bed for modern ideas of self-organization and scaling. Finally, deformation mechanisms in earth materials are extremely sensitive to environmental factors, especially water. This factor alone explains most differences between large-scale deformation structures observed on Earth and those on the other terrestrial planets. Current problems in the Earth sciences that require a better understanding of material behavior include the mechanics of the earthquake instability, the migration of magma in the crust, the source and dynamical significance of observed heterogeneity in the deep interior, and the generation of the magnetic field.     

Life as a cosmic imperative?

The origin of life on Earth may be divided into two stages separated by the first appearance of replicable molecules, most probably of RNA. The first stage depended exclusively on chemistry. The second stage likewise involved chemistry, but with the additional participation of selection, a necessary concomitant of inevitable replication accidents. Consideration of these two processes suggests that the origin of life may have been close to obligatory under the physical-chemical conditions that prevailed at the site of its birth. Thus, an extrasolar planet in which those conditions were replicated appears as a probable site for the appearance of extra-terrestrial life.     

A Zinc–Dual-Halogen Battery with a Molten Hydrate Electrolyte

Halogen redox couples offer several advantages for energy storage such as low cost, high solubility in water, and high redox potential. However, the operational complexity of storing halogens at the oxidation state via liquid-phase media hampers their widespread application in energy-storage devices. Herein, an aqueous zinc–dual-halogen battery system taking the advantages of redox flow batteries (inherent scalability) and intercalation chemistry (high capacity) is designed and fabricated. To enhance specific energy, the designed cell exploits both bromine and chlorine as the cathode redox couples that are present as halozinc complexes in a newly developed molten hydrate electrolyte, which is distinctive to the conventional zinc–bromine batteries. Benefiting from the reversible uptake of halogens at the graphite cathode, exclusive reliance on earth-abundant elements, and membrane-free and possible flow-through configuration, the proposed battery can potentially realize high-performance massive electric energy storage at a reasonable cost.     

Fear, pandemonium, equanimity and delight: human responses to extra-terrestrial life

How will people respond to the discovery of extra-terrestrial life? Potentially useful resources for addressing this question include historical prototypes, disaster studies and survey research. Reactions will depend on the interplay of the characteristics of the newly found life, the unfolding of the discovery, the context and content of the message and human information processing as shaped by biology, culture and psychology. Pre-existing images of extra-terrestrials as god-like, demonic, or artificial will influence first impressions that may prove highly resistant to change. Most probably people will develop comprehensive images based on minimal information and assess extra-terrestrials in the same ways that they assess one another. Although it is easy to develop frightening scenarios, finding microbial life in our Solar System or intercepting a microwave transmission from many light years away are less likely to be met with adverse reactions such as fear and pandemonium than with positive reactions such as equanimity and delight.     

The Planetary and Space Simulation Facilities at DLR Cologne

Astrobiology strives to increase our knowledge on the origin, evolution and distribution of life, on Earth and beyond. In the past centuries, life has been found on Earth in environments with extreme conditions that were expected to be uninhabitable. Scientific investigations of the underlying metabolic mechanisms and strategies that lead to the high adaptability of these extremophile organisms increase our understanding of evolution and distribution of life on Earth. Life as we know it depends on the availability of liquid water. Exposure of organisms to defined and complex extreme environmental conditions, in particular those that limit the water availability, allows the investigation of the survival mechanisms as well as an estimation of the possibility of the distribution to and survivability on other celestial bodies of selected organisms. Space missions in low Earth orbit (LEO) provide access for experiments to complex environmental conditions not available on Earth, but studies on the molecular and cellular mechanisms of adaption to these hostile conditions and on the limits of life cannot be performed exclusively in space experiments. Experimental space is limited and allows only the investigation of selected endpoints. An additional intensive ground based program is required, with easy to access facilities capable to simulate space and planetary environments, in particular with focus on temperature, pressure, atmospheric composition and short wavelength solar ultraviolet radiation (UV). DLR Cologne operates a number of Planetary and Space Simulation facilities (PSI) where microorganisms from extreme terrestrial environments or known for their high adaptability are exposed for mechanistic studies. Space or planetary parameters are simulated individually or in combination in temperature controlled vacuum facilities equipped with a variety of defined and calibrated irradiation sources. The PSI support basic research and were recurrently used for pre-flight test programs for several astrobiological space missions. Parallel experiments on ground provided essential complementary data supporting the scientific interpretation of the data received from the space missions.     

Discovery of extra-terrestrial life: assessment by scales of its importance and associated risks

The Rio Scale accepted by the SETI Committee of the International Academy of Astronautics in 2002 is intended for use in evaluating the impact on society of any announcement regarding the discovery of evidence of extra-terrestrial (ET) intelligence. The Rio Scale is mathematically defined using three parameters (class of phenomenon, type of discovery and distance) and a δ factor, the assumed credibility of a claim. This paper proposes a new scale applicable to announcements alleging evidence of ET life within or outside our Solar System. The London Scale for astrobiology has mathematical structure and logic similar to the Rio Scale, and uses four parameters (life form, nature of phenomenon, type of discovery and distance) as well as a credibility factor δ to calculate a London Scale index (LSI) with values ranging from 0 to 10. The level of risk or biohazard associated with a purported discovery is evaluated independently of the LSI value and may be ranked in four categories. The combined information is intended to provide a scalar assessment of the scientific importance, validity and potential risks associated with putative evidence of ET life discovered on Earth, on nearby bodies in the Solar System or in our Galaxy.     

Nanofluidic redox cycling amplification for the selective detection of catechol

We have developed a chip-based nanofluidic device to amplify the electrochemical signal of catechols by orders of magnitude. The amplification is based on rapid redox cycling between plane parallel electrodes inside a nanochannel. We show that it is possible to monitor the signal of only a few hundred molecules residing in the active area of the nanofluidic sensor. Furthermore, due to the nanochannel design, the sensor is immune to interference by molecules undergoing irreversible redox reactions. We demonstrate the selectivity of the device by detecting catechol in the presence of ascorbic acid, whose oxidized form is only stable for a short time. The interference of ascorbic acid is usually a challenge in the detection of catecholamines in biological samples.     

Is life what we make of it?

Although astrobiological or SETI detections are possible, actual invasions of sentient extra-terrestrials or plagues of escaped alien microbes are unlikely. Therefore, an anthropological perspective on the question suggests that in the event of a detection, the vast majority of humanity will be dealing not with extra-terrestrial life itself (whether intelligent or not, local or distant), but with human perceptions and representations of that alien life. These will, inevitably, derive from the powerful influences of culture and individual psychology, as well as from science. It may even be argued that in most detection scenarios, the scientific data (and debates about their interpretation) will be nigh-irrelevant to the unfolding of international public reaction. 'Extra-terrestrial life' will, in short, go wild. From this premise, some key questions emerge, including: what can scientists reasonably do to prepare, and what should their responsibilities be, particularly with respect to information dissemination and public discussions about policy? Then, moving beyond the level of immediate practicalities, we might also ask some more anthropological questions: what are the cultural substrates underneath the inquiries of Western science into extra-terrestrial life? In particular, what are the stories we have been told about discovery of rare life, and about contact with other beings, and do these stories really mean what we think they do? Might a closer look at those narratives help us gain perspective on the quest to find extra-terrestrial life, and on our quest to prepare for the consequences of detection?     

Supra-Earth affairs

The United Nations briefly considered the issue of extra-terrestrial intelligence at the 32nd session of the General Assembly in 1977. As a result, the Office of Outer Space Affairs was tasked to prepare a document on issues related to 'messages to extra-terrestrial civilizations', but this area has not been followed through in more recent times. This discussion paper describes the United Nations' activities in the field of near-Earth objects in some detail, and suggests that this might be used as a model of how Member States could proceed with dealing with this issue in case the existence of extra-terrestrial life/intelligence is established.     

Submicrometer hyperspectral X-ray imaging of heterogeneous rocks and geomaterials: applications at the Fe k-edge

Because of their complex genesis, rocks and geomaterials are commonly polycrystalline heterogeneous systems, with various scale-level chemical and structural heterogeneities. Like most other μ-analytical techniques relying on scanning instruments with pencil-beam, the X-ray absorption near edge structure (XANES) technique allows elemental oxidation states to be probed with high spatial resolution but suffers from long acquisition times, imposing practical limits on the field of view. Now, regions of interest of sample are generally several orders of magnitude larger than the beam size. Here, we show the potential of coupling XANES and full-field absorption radiographies with a large hard X-ray beam. Thanks to a new setup, which allows both the acquisition of a XANES image stack and the execution of polarization contrast imaging, 1 to 4 mega-pixel crystallographic orientations and Fe oxidation state mapping corrected from polarization effects are obtained in a couple of hours on polycrystalline materials with submicrometric resolution. The demonstration is first carried out on complex metamorphic rocks, where Fe(3+)/Fe(total) images reveal subtle redox variations within single mineralogical phases. A second application concerns a bentonite analogue considered for nuclear waste and CO(2) storage. Proportion mappings of finely mixed phases are extracted from hyperspectral data, imaging the spatial progress of reaction processes essential for the safety of such storage systems.     

The detection of extra-terrestrial life and the consequences for science and society

Astronomers are now able to detect planets orbiting stars other than the Sun where life may exist, and living generations could see the signatures of extra-terrestrial life being detected. Should it turn out that we are not alone in the Universe, it will fundamentally affect how humanity understands itself--and we need to be prepared for the consequences. A Discussion Meeting held at the Royal Society in London, 6-9 Carlton House Terrace, on 25-26 January 2010, addressed not only the scientific but also the societal agenda, with presentations covering a large diversity of topics.     

Extractive electrospray ionization mass spectrometry-enhanced sensitivity using an ion funnel

Electrodynamic ion funnel interfaces for electrospray ionization (ESI) have shown to enhance the sensitivity of measurements by more than 2 orders of magnitude in the intermediate pressure region of the instrument (1-30 Torr). In this study, we use an ion funnel at ambient pressure to enhance the sensitivity of extractive electrospray ionization (EESI) by spraying directly into the ion funnel. EESI is a powerful ionization technique that is capable of handling complex matrixes that may contain dozens of compounds. Our results using atenolol, salbutamol, and cocaine as test compounds show that we can improve the limit of detection for these compounds by more than 3 orders of magnitude compared to standard EESI experiments.