Exoplanets - search methods, discoveries, and prospects for astrobiology

Whereas the Solar System has Mars and Europa as the best candidates for finding fossil/extant life as we know it - based on complex carbon compounds and liquid water - the 263 (non-pulsar) planetary systems around other stars as known at 15 September 2008 could between them possess many more planets where life might exist. Moreover, the number of these exoplanetary systems is growing steadily, and with this growth there is an increase in the number of planets that could bear carbon-liquid water life. In this brief review the main methods by which exoplanets are being discovered are outlined, and then the discoveries that have so far been made are presented. Habitability is then discussed, and an outline presented of how a planet could be studied from afar to determine whether it is habitable, and whether it is indeed inhabited. This review is aimed at the astrobiology community, which spans many disciplines, few of which involve exoplanets. It is therefore at a basic level and concentrates on the major topics.Comment: 37 pages, 12 Figure

Dual wound dc brush motor gearhead

The design requirements, the design, development tests and problems, the qualification and life test and the findings of the strip examination of a dual wound DC brushed motor gearhead are described. It is the only space qualified dual wound dc brushed motor gearhead in Europe

Stationary solution of the ring-spinning balloon in zero air drag using a RBFN based mesh-free method

A technique for numerical analysis of the dynamics of the ring-spinning balloon based on the Radial Basis Function Networks (RBFNs) is presented in this paper. This method uses a 'universal approximator' based on neural network methodology to solve the differential governing equations which are derived from the conditions of the dynamic equilibrium of the yarn to determine the shape of balloon yarn. The method needs only a coarse finite collocation points without any finite element-type discretisation of the domain and its boundary for numerical solution of the governing differential equations. This paper will report a first assessment of the validity and efficiency of the present mesh-less method in predicting the balloon shape across a wide range of spinning conditions

The Stability of the orbits of Earth-mass planets in and near the habitable zones of known exoplanetary systems

We have shown that Earth-mass planets could survive in variously restricted regions of the habitable zones (HZs) of most of a sample of nine of the 93 main-sequence exoplanetary systems confirmed by May 2003. In a preliminary extrapolation of our results to the other systems, we estimate that roughly a third of the 93 systems might be able to have Earth-mass planets in stable, confined orbits somewhere in their HZs. Clearly, these systems should be high on the target list for exploration for terrestrial planets. We have reached this conclusion by launching putative Earth-mass planets in various orbits and following their fate with a mixed-variable symplectic integrator

Mars before the Space Age

Mars has surely been scrutinised since the dawn of humankind. Its appearance every couple of years like a drop of blood in the sky led to warlike attributes in the ancient world. In the 16th century Tycho Brahe made accurate observations of the position of Mars that enabled Johannes Kepler to obtain his first two laws of planetary motion. These in turn were explained by Newton's laws of motion and gravity. In the 17th century the first telescope observations were made, but Mars is small and very little surface detail could be discerned. Throughout the 18th and 19th centuries telescopes improved, revealing many dark areas on the red tinted surface. During the close opposition of 1877 sufficient detail could be seen that enabled Giovanni Schiaparelli to announce that he could see about 40 canali on Mars. This led to the saga of the canals of Mars, finally laid to rest in 1971 when Mariner 9 made observations from Martian orbit showing that the canali/canals do not exist. Belief that there was life on Mars was widespread in the 19th century. However, the majority of astronomers never believed in Martian intelligence. Least controversial was the view that the dark areas were some form of plant life. This view persisted until Mariner 4 flew past Mars in 1965 and discovered a far thinner atmosphere than previously thought. This was a low point, with impact craters dominating the images. It was Mariner 9 that revealed much more promising landscapes, including volcanic features, and others indicating that water had flowed across the surface, particularly when Mars was young. Thus, the contemporary era of Mars exploration began. Our picture of Mars today is not only much more complete than that before Mariner 4, in several ways it is quite different. The belief, however, that there might be life on Mars persists – subsurface life cannot be ruled out and, failing that, there might be ancient fossils on Mars

Habitability of known exoplanetary systems based on measured stellar properties

At present, because of observational selection effects, we know of no exoplanetary systems with any planetary masses close to that of the Earth. We have therefore used computer models to see whether such planets could be dynamically stable in the presence of the more massive planets known to be present, and in particular whether planets with roughly an Earth mass could remain confined to the classical habitable zone (HZ) for long enough for life to have emerged. Measured stellar properties have been used to determine for each system the present location of the HZ. We have also determined the critical distances from the orbit of each giant planet within which an Earth-mass planet would suffer large orbital changes. We then evaluated the present habitability of each and every exoplanetary system by examining the penetration of these critical distances into the HZ. The critical distances can be obtained by extensive computer modelling of an exoplanetary system. This is far too time consuming to apply to all of the 150 or so systems already known, and to keep up with the latest discoveries. Therefore, in earlier work we studied a few systems in great detail, and developed a speedier means of obtaining the critical distances. We summarize this comparatively quick method here. We can then evaluate comparatively quickly the present habitability of each exoplanetary system by examining the penetration of the critical distance(s) into the HZ. The results are encouraging for astrobiology.Comment: Accepted for publication by The Astrophysical Journal. A few revisions have been made following suggestions by the refere

Neuropsychological functioning and OROS® methylphenidate in an Adult Attention-Deficit/Hyperactivity Disorder (ADHD) population

posterObjective: Neuropsychological tests have been used in attention-deficit/hyperactivity disorder (ADHD) to compare ADHD patients with normal subjects, to assess drug-placebo differences in clinical trials and to identify appropriate medication levels via test dose paradigms. While clinical studies have generally been positive1 with moderate effect sizes, outcomes have been inconsistent, particularly in adults. This analysis examined a neurocognitive battery in a sample of adult ADHD subjects during a clinical trial of OROS® methylphenidate (OROS MPH; Concerta®).2 Methods:This 8-week crossover study utilized OROS MPH in 41 subjects who met DSM-IV criteria and the Utah Criteria for ADHD. ADHD symptoms were assessed using the Wender-Reimherr Adult Attention Deficit Disorder Scale (WRAADDS)3 and the ADHD-Rating Scale (ADHD-RS). (The primary efficacy and safety results were previously reported.2) The CNS Vital Signs (CNSVS) is a computer-based neurocognitive battery with tests of Verbal and Visual Memory, Finger Tapping, Symbol Digit Coding (SDC), the Stroop Test, the Shifting Attention Test (SAT), and the Continuous Performance Test (CPT). The developer has reported average scores for both normal and ADHD subjects on these tests.4 Baseline scores on this population were compared with the normative data. The impact of treatment (OROS MPH vs placebo) on test scores was assessed via paired t-tests. Results: OROS MPH was superior to placebo for all clinical ADHD measures, including total WRAADDS (44% vs 13% improvement; P=0.001), plus the subscales addressing inattention, hyperactivity/impulsivity, and emotional dysregulation. At baseline, our ADHD patients had CNSVS scores midway between the developer's ADHD and normal samples. However, on errors in the Stroop and CTP commission errors, the ADHD patients scored worse than either comparison group. Although OROS MPH was usually associated with better scores than placebo, this difference only achieved significance for 4 of the tests: SDC number correct (P=0.041), Stroop complex reaction time (P=0.009), SAT number correct (P=0.018), and CPT reaction time (P=0.034). Conclusions: Baseline scores were consistently worse than the test developer's normative data, and endpoint scores on OROS MPH were consistently better than placebo. The tests that reached or approached significance were all test scores that had previously reached significance in test dose paradigms. The longer period between testing in this clinical trial (4 weeks) compared with a test dose paradigm (1 hour) may contribute to the weaker relationship. Conversely, actual clinical trials in adults with ADHD have frequently failed to find drug-placebo differences on cognitive testing

Estimation of stratospheric input to the Arctic troposphere: 7Be and 10Be in aerosols at Alert, Canada

Concentrations of 7Be and 210Pb in 2 years of weekly high-volume aerosol samples collected at Alert, Northwest Territories, Canada, showed pronounced seasonal variations. We observed a broad winter peak in 210Pb concentration and a spring peak in 7Be. These peaks were similar in magnitude and duration to previously reported results for a number of stations in the Arctic Basin. Beryllium 10 concentrations (determined only during the first year of this study) were well correlated with those of 7Be; the atom ratio 10Be/7Be was nearly constant at 2.2 throughout the year. This relatively high value of 10Be/7Be indicates that the stratosphere must constitute an important source of both Be isotopes in the Arctic troposphere throughout the year. A simple mixing model based on the small seasonal variations of 10Be/7Be indicates an approximately twofold increase of stratospheric influence in the free troposphere in late summer. The spring maxima in concentrations of both Be isotopes at the surface apparently reflect vertical mixing in rather than stratospheric injections into the troposphere. We have merged the results of the Be-based mixing model with weekly O3 soundings to assess Arctic stratospheric impact on the surface O3 budget at Alert. The resulting estimates indicate that stratospheric inputs can account for a maximum of 10-15% of the 03 at the surface in spring and for less during the rest of the year. These estimates are most uncertain during the winter. The combination of Be isotopic measurements and O3 vertical profiles could allow quantification of the contributions of O3 from the Arctic stratosphere and lower latitude regions to the O3 budget in the Arctic troposphere. Although at present the lack of a quantitative understanding of the temporal variation of O3 lifetime in the Arctic troposphere precludes making definitive calculations, qualitative examples of the power of this approach are given