Energy, chemical disequilibrium, and geological constraints on Europa

Europa is a prime target for astrobiology. The presence of a global subsurface liquid water ocean and a composition likely to contain a suite of biogenic elements make it a compelling world in the search for a second origin of life. Critical to these factors, however, may be the availability of energy for biological processes on Europa. We have examined the production and availability of oxidants and carbon-containing reductants on Europa to better understand the habitability of the subsurface ocean. Data from the Galileo Near-Infrared Mapping Spectrometer were used to constrain the surface abundance of CO(2) to 0.036% by number relative to water. Laboratory results indicate that radiolytically processed CO(2)-rich ices yield CO and H(2)CO(3); the reductants H(2)CO, CH(3)OH, and CH(4) are at most minor species. We analyzed chemical sources and sinks and concluded that the radiolytically processed surface of Europa could serve to maintain an oxidized ocean even if the surface oxidants (O(2), H(2)O(2), CO(2), SO(2), and SO(4) (2)) are delivered only once every approximately 0.5 Gyr. If delivery periods are comparable to the observed surface age (30-70 Myr), then Europa's ocean could reach O(2) concentrations comparable to those found in terrestrial surface waters, even if approximately 10(9) moles yr(1) of hydrothermally delivered reductants consume most of the oxidant flux. Such an ocean would be energetically hospitable for terrestrial marine macrofauna. The availability of reductants could be the limiting factor for biologically useful chemical energy on Europa.     

Equivalence of the Likelihood Ratio Processor, the Maximum Signal-to-Noise Ratio Filter, and the Wiener Filter

It is shown that for the problem of detecting a nonfluctuating target in Gaussian noise, three common optimality criteria lead to identical multichannel filter designs.     

Carpe diem: Europe must make a genuine space policy now

This article examines the current effort to establish a ‘European space policy’. The authors place this effort in the context of the experience of the 2003 Green and White Papers, the subsequent stalling of the Constitutional Treaty for the EU, and reductions in the EU's financial perspectives. They argue that, despite post-referenda malaise and systemic inertia on the part of several member states, adoption of a space policy is long overdue and should not merely seek to rearrange what is already there or expose yet again what is being done. A full-blooded policy setting in train fundamental change is needed, justifying a political decision at the level of the European Council. The article then offers criteria such a policy should fulfil as well as items the authors view as essential content. They briefly explore issues which could become stumbling blocks but which can be accommodated within the kind of policy this article advocates.     

Side zone automotive radar

Side Detection System (SDS) based on radar technology for automotive applications is introduced. The functional requirements of such a system are described and the resulting safety enhancement benefits are summarized. Also, the nature of the radar environment for the side zone application is reviewed in qualitative terms. Minimizing cost is a necessary system design driver, and presents a considerable challenge for radar designs in all but the most primitive capability cases. A cost effective design approach and radar system architecture which solves the side zone application problem of separating potentially hazardous target returns from exorbitant amounts of clutter are discussed in some detail. This design has been in road test for several months, and has achieved enthusiastic customer acceptance     

A Model for the Radar Echo from a Random Collection of Rotating Dipole Scatterers

A theoretical model for the radar echo from a random collection of dipole scatterers is presented. The analysis of the model takes into account the effects of scatterer rotation which have been neglected in previous related work. It is shown that rotational motion of the scaterers can have significant effects upon the echo waveform. The fluctuating characteristics of clutter echoes are also investigated. The theory and some experimental results in the literature are shown to be in relatively good agreement.     

Quantization Noise in Digital Moving Target Indication Systems

This paper deals precisely with the effect of quantum or step size in an analog-to-digital converter on the quantization noise in the output of MTI (moving target indication) radar processors. The correlation between quantization errors on successive pulses is considered in the analysis and is shown to have a small quieting effect on the output quantization noise.     

Early commercial demonstration of space solar power using ultra-lightweight arrays

Space solar power shows great promise for future energy sources worldwide. Most central power stations operate with power capacity of 1000 MW or greater. Due to launch size limitations and specific power of current, rigid solar arrays, the largest solar arrays that have flown in space are around 50 kW. Thin-film arrays offer the promise of much higher specific power and deployment of array sizes up to several MW with current launch vehicles. An approach to early commercial applications for space solar power to distribute power to charge hand-held, mobile battery systems by wireless power transmission (WPT) from thin-film solar arrays in quasi-stationary orbits will be presented. Four key elements to this prototype will be discussed: (1) Space and near-space testing of prototype wireless power transmission by laser and microwave components including WPT space to space and WPT space to near-space HAA transmission demonstrations; (2) distributed power source for recharging hand-held batteries by wireless power transmission from MW space solar power systems; (3) use of quasi-geostationary satellites to generate electricity and distribute it to targeted areas; and (4) architecture and technology for ultra-lightweight thin-film solar arrays with specific energy exceeding 1 kW/kg. This approach would yield flight demonstration of space solar power and wireless power transmission of 1.2 MW. This prototype system will be described, and a roadmap will be presented that will lead to still higher power levels.     

Biogenicity of morphologically diverse carbonaceous microstructures from the ca. 3400 Ma Strelley pool formation, in the Pilbara Craton, Western Australia

Morphologically diverse structures that may constitute organic microfossils are reported from three remote and widely separated localities assigned to the ca. 3400?Ma Strelley Pool Formation in the Pilbara Craton, Western Australia. These localities include the Panorama, Warralong, and Goldsworthy greenstone belts. From the Panorama greenstone belt, large (> 40?μm) lenticular to spindle-like structures, spheroidal structures, and mat-forming thread-like structures are found. Similar assemblages of carbonaceous structures have been identified from the Warralong and Goldsworthy greenstone belts, though these assemblages lack the thread-like structures but contain film-like structures. All structures are syngenetic with their host sedimentary black chert, which is associated with stromatolites and evaporites. The host chert is considered to have been deposited in a shallow water environment. Rigorous assessment of biogenicity (considering composition, size range, abundance, taphonomic features, and spatial distributions) suggests that cluster-forming small (<15 μm) spheroids, lenticular to spindle-like structures, and film-like structures with small spheroids are probable microfossils. Thread-like structures are more likely fossilized fibrils of biofilm, rather than microfossils. The biogenicity of solitary large (>15?μm) spheroids and simple film-like structures is less certain. Although further investigations are required to confirm the biogenicity of carbonaceous structures from the Strelley Pool Formation, this study presents evidence for the existence of morphologically complex and large microfossils at 3400?Ma in the Pilbara Craton, which can be correlated to the contemporaneous, possible microfossils reported from South Africa. Although there is still much to be learned, they should provide us with new insights into the early evolution of life and shallow water ecosystems.     

Clathrate hydrates of oxidants in the ice shell of Europa

Europa's icy surface is radiolytically modified by high-energy electrons and ions, and photolytically modified by solar ultraviolet photons. Observations from the Galileo Near Infrared Mapping Spectrometer, ground-based telescopes, the International Ultraviolet Explorer, and the Hubble Space Telescope, along with laboratory experiment results, indicate that the production of oxidants, such as H2O2, O2, CO2, and SO2, is a consequence of the surface radiolytic chemistry. Once created, some of the products may be entrained deeper into the ice shell through impact gardening or other resurfacing processes. The temperature and pressure environments of regions within the europan hydrosphere are expected to permit the formation of mixed clathrate compounds. The formation of carbon dioxide and sulfur dioxide clathrates has been examined in some detail. Here we add to this analysis by considering oxidants produced radiolytically on the surface of Europa. Our results indicate that the bulk ice shell could have a approximately 1.7-7.6% by number contamination of oxidants resulting from radiolysis at the surface. Oxidant-hosting clathrates would consequently make up approximately 12-53% of the ice shell by number relative to ice, if oxidants were entrained throughout. We examine, in brief, the consequences of such contamination on bulk ice shell thickness and find that clathrate formation could lead to substantially thinner ice shells on Europa than otherwise expected. Finally, we propose that double occupancy of clathrate cages by O2 molecules could serve as an explanation for the observation of condensed-phase O2 on Europa. Clathrate-sealed, gas-filled bubbles in the near surface ice could also provide an effective trapping mechanism, though they cannot explain the 5771 A (O2)2 absorption.     

Letting thoughts take wing

Recent developments in neuroelectronics are applied to aviation and airplane flight control instruments. Electromyographic control has been applied to flight simulations using the autopilot interface in order to use gestures to give bank and pitch commands to the autopilot. In other demonstrations, direct rate control was used to perform repeated successful landings and the damage-adaptive capability of inner-loop neural and propulsion-based controls was utilized.