Editorial
The special issue devoted to papers from the Astrobiology Society of Britain Conference 2006
- M.J. Burchell
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- Published online by Cambridge University Press:
- 14 December 2006, p. 181
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The Astrobiology Society of Britain (http://www.astrobiologysociety.org/) held its second conference (Life Here, There and Everywhere) in April 2006. The meeting was hosted by the University of Kent and took place on campus in Canterbury from 18–21 April. A total of 48 abstracts were submitted to the meeting. The final schedule featured 35 talks and 14 posters on a range of topics which included Mars, the Moon, comets, exoplanets, impacts, outreach and analytic techniques – all with an astrobiology flavour. With 62 attendees (including overseas delegates from Sweden, Spain, Portugal, Australia and the United States) the meeting also allowed for strong social interaction (and the building of new collaborations and networking) as well as showcasing ongoing research in the field.
Research Article
Looking towards the detection of exoearths with SuperWASP
- R.A. Street, D.J. Christian, W.I. Clarkson, A.C. Cameron, B. Enoch, A. Evans, A. Fitzsimmons, C.A. Haswell, C. Hellier, S.T. Hodgkin, Keith Horne, J. Irwin, F.P. Keenan, S.R. Kane, T.A. Lister, A.J. Norton, J. Osborne, D. Pollacco, R. Ryans, I. Skillen, R.G. West, P.J. Wheatley, D. Wilson
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- 18 September 2006, pp. 183-186
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The WASP consortium is conducting an ultra-wide field survey of stars between 8–15 mag from both hemispheres. Our primary science goal is to detect extra-solar ‘hot-Jupiter’-type planets that eclipse (or transit) bright host stars and for which further detailed investigation will be possible. We summarize the design of the SuperWASP instruments and describe the first results from our northern station SW-N, sited in La Palma, Canary Islands. Our second station, which began operations this year, is located at the South African Astronomical Observatory. Between April and September, 2004, SW-N continuously observed ~6.7 million stars. The consortium's custom-written, fully automated data reduction pipeline has been used to process these data, and the information is now stored in the project archive, held by the Leicester database and archive service (LEDAS). We have applied a sophisticated, automated algorithm to identify the low-amplitude (~0.01 mag), brief (~few hours) signatures of transiting exoplanets. In addition, we have assessed each candidate in the light of all available catalogue information in order to reject data artefacts and astrophysical false positive detections. The highest priority candidates are currently being subjected to further observations in order to select the true planets. Once the exoplanets are confirmed, a host of exciting opportunities are open to us. In this paper, we describe two techniques that exploit the transits in order to detect other objects within the same system. The first involves determining precise epochs for a sequence of transit events in order to detect the small timing variations caused by the gravitational pull of other planets in the same system. The second method employs ultra-high precision photometry of the transits to detect the deviations caused by the presence of exoplanetary moons. Both of these techniques are capable of detecting objects the size of terrestrial planets.
Persistent hazardous environments around stars older than the Sun
- J.S. Greaves
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- 19 October 2006, pp. 187-190
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Collisions amongst comets create belts of orbiting debris and, by using submillimetre wavelength observations, these collision zones can be imaged around nearby stars. An image of the closest Solar analogue, τ Ceti, shows that it possesses at least 20 times the content of the outer Solar System in cool debris particles. The inferred population of parent colliders is around 1 M[oplus ], also much larger than in the Sun's Kuiper Belt of comets. This system represents a different evolutionary outcome for a Sun-like star, with no Jupiter-like planet but many cometary bodies, and thus a potentially heavy and prolonged history of impacts on any inner terrestrial planets. Since τ Ceti is 10 Gyr old, life would have had to deal with massive bombardment over very long timescales. Furthermore, impactors in the 10 km-upwards class could arrive at intervals of 1 Myr or less, longer than recovery times on Earth, and so similar biology is unlikely. It is presently unknown whether nearby stars typically have comet belts similar to that of the Sun or of τ Ceti; extrapolations of existing data suggest many stars could be at least 2–5 times above the Solar debris level. Future large telescopes will be able to probe down to Solar System levels of cometary debris.
The astrobiological case for renewed robotic and human exploration of the Moon
- I.A. Crawford
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- Published online by Cambridge University Press:
- 30 August 2006, pp. 191-197
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An ambitious programme of lunar exploration will reveal much of astrobiological interest. Examples include: (i) better characterization of the impact cratering rate in the Earth–Moon system, with implications for understanding the possible ‘impact frustration’ of the origin of life; (ii) preservation of ancient meteorites blasted off Earth, Mars and Venus, which may preserve evidence of the early surface environments of these planets, as well as constraining models of lithopanspermia; (iii) preservation of samples of the Earth's early atmosphere not otherwise available; (iv) preservation of cometary volatiles and organics in permanently shadowed polar craters, which would help elucidate the importance of these sources in ‘seeding’ the terrestrial planets with pre-biotic materials; and (v) possible preservation of extraterrestrial artefacts on the lunar surface, which may permit limits to be placed on the prevalence of technological civilizations in the Galaxy. Much of this valuable information is likely to be buried below the present surface (e.g. in palaeoregolith deposits) and will require a considerable amount of geological fieldwork to retrieve. This would be greatly facilitated by a renewed human presence on the Moon, and may be wholly impractical otherwise. In the longer term, such lunar operations would pave the way for the human exploration of Mars, which may also be expected to yield astrobiological discoveries not otherwise obtainable.
On the possibility of terrestrial planet formation in hot-Jupiter systems
- Martyn J. Fogg, Richard P. Nelson
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- 30 August 2006, pp. 199-209
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About a fifth of the exoplanetary systems that have been discovered contain a so-called hot-Jupiter – a giant planet orbiting within 0.1 AU of the central star. Since these stars are typically of the F/G spectral type, the orbits of any terrestrial planets in their habitable zones at ~1 AU should be dynamically stable. However, because hot-Jupiters are thought to have formed in the outer regions of a protoplanetary disc, and to have then migrated through the terrestrial planet zone to their final location, it is uncertain whether terrestrial planets can actually grow and be retained in these systems. In this paper we review attempts to answer this question. Initial speculations, based on the assumption that migrating giant planets will clear planet-forming material from their swept zone, all concluded that hot-Jupiter systems should lack terrestrial planets. We show that this assumption may be incorrect, for when terrestrial planet formation and giant planet migration are simulated simultaneously, abundant solid material is predicted to remain from which terrestrial planet growth can resume.
WatSen: searching for clues for water (and life) on Mars
- Monica M. Grady
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- 12 October 2006, pp. 211-219
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There is plenty of evidence for fluid on Mars: large-scale (planet-wide) features have been captured over four decades by a procession of orbiting satellites equipped with cameras with increasingly higher spatial resolutions. Imagery of the surface shows channels, valleys, ice-caps, etc. Small-scale, more local evidence for fluid has come from images obtained by rovers on the Martian surface. Images that water produced many of the features are supported by spectroscopic measurements (again both planet-wide and local) over a range of wavelengths, which show the presence of minerals generally only produced in the presence of water (haemetite, jarosite, etc.). Results from meteorites continue this picture of fluid activity taking place over significant periods of Mars' history. Despite all these indicators of water, direct detection of water has never been performed. We have reviewed the evidence for water on Mars' surface, and have described WatSen, a combined humidity sensor and infrared IR detector, which can be employed to search for water at and below Mars' surface. WatSen is designed to be part of the suite of instruments on the mole that will be deployed as part of the Geophysics and Environment Package on ExoMars. The objectives of the package are as follows: (i) to detect water within Martian soil by measuring humidity and IR spectral characteristics of the substrate at surface and at depth; (ii) to determine the mineralogy and mineral chemistry of surface soils (this measurement will provide the mineralogical context for the elemental results that come from other instruments mounted on the landing platform); (iii) to determine how mineralogy changes with depth. The utility of WatSen is that it will not only detect the presence of water, but will also be able to record which minerals are present and their chemistry; it is also sensitive to many organic species. WatSen is a new instrument concept specifically designed to search for clues of the presence of water, and to look for evidence of life on Mars.
The ExoMars rover and Pasteur payload Phase A study: an approach to experimental astrobiology
- Dave Barnes, Enrico Battistelli, Reinhold Bertrand, Francesco Butera, Raja Chatila, Alessandro Del Biancio, Chris Draper, Alex Ellery, Rolando Gelmi, Felix Ingrand, Charles Koeck, Simon Lacroix, Pierre Lamon, Chris Lee, Piergiovanni Magnani, Nildeep Patel, Carlo Pompei, Eduardo Re, Lutz Richter, Mark Rowe, Roland Siegwart, Richard Slade, Mark F Smith, Gregoire Terrien, Ronan Wall, Roger Ward, Lester Waugh, Mark Woods
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- 20 September 2006, pp. 221-241
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The Aurora programme is the European Space Agency programme of planetary exploration focused primarily on Mars. Although the long-term goals of Aurora are uncertain, the early phases of the Aurora programme are based on a number of robotic explorer missions – the first of these is the ExoMars rover mission currently scheduled for launch in 2013 (originally 2011). The ExoMars rover – developed during a Phase A study – is a 240 kg Mars rover supporting a 40 kg payload (called Pasteur) of scientific instruments specifically designed for astrobiological prospecting to search for evidence of extant or extinct life. In other words, ExoMars represents a new approach to experimental astrobiology in which scientific instruments are robotically deployed at extraterrestrial environments of astrobiological interest. Presented is an outline of the design of the rover, its robotic technology, its instrument complement and aspects of the design decisions made. ExoMars represents a highly challenging mission, both programmatically and technologically. Some comparisons are made with the highly successful Mars Exploration Rovers, Spirit and Opportunity.
W(h)ither the Drake equation?
- Mark J. Burchell
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- 19 September 2006, pp. 243-250
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For over 40 years the formalism known as the Drake equation has helped guide speculation about the likelihood of intelligent extraterrestrial life contacting us. Since the equation was formulated there have been significant advances in astronomy and astrophysics, sufficient to merit a review of the significance of the Drake equation. The equation itself is as a series of terms which, when combined, allow an informed discussion of the likelihood of contact with an alien intelligence. However, whilst it has a mathematical form (i.e. a series of terms multiplied together to give an overall probability) it is best understood not as an equation in the strictly mathematical sense. Some of the terms have a physically quantifiable, numerically based meaning (e.g. obtainable from astronomy) and some are more social in content in that they describe the behaviour and evolution of societies and thus are more social science in nature and not truly estimable without observation of a set of societies. Initially, almost all the terms had to be estimated based on informed guesswork or belief. However, in the intervening period since the early 1960s, many of the a priori scientific terms which were themselves initially so uncertain as to require estimation by guess work or belief are now, or will soon be, directly measurable from current or planned astronomical projects. This leaves the non-scientific terms as a distinct class of their own, still subject to analysis only by discussion. Thus observational astronomy has nearly caught up with parts of the Drake equation and will soon quantify the purely physical science parts of the equation. The social parts (concerning intelligent societies, etc.) are still a priori unknowable. In addition, the growth of the subject called astrobiology (i.e. the study of life in the Universe) has developed so fast that communicating with intelligent life is now increasingly seen as just one small part of a much larger discipline. The knowledge as to whether there is life per se (apart from on Earth) in our galactic neighbourhood may be obtainable in the near future directly from observation. Such knowledge will have a profound impact on mankind and will be obtained without the form of communication envisaged by the Drake equation.
Which exoplanetary systems could harbour habitable planets?
- Barrie W. Jones, P. Nick Sleep, David R. Underwood
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- 12 October 2006, pp. 251-259
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Habitable planets are likely to be broadly Earth-like in composition, mass and size. Masses are likely to be within a factor of a few Earth masses – we call such planets Earth-mass planets. It is important to find such planets. Currently, we do not have sufficiently sensitive techniques to detect planets with such small masses, except in rare circumstances. It is thus necessary to model the known exoplanetary systems to see whether Earth-mass planets could be present. In particular, we need to establish whether such planets could be present in the classical habitable zone (HZ), or whether the giant planets that we know to be present have gravitationally ejected Earth-mass planets or prevented their formation. We have answered this question by applying computer models to the 152 exoplanetary systems known as of 18 April 2006 that are sufficiently well characterized for our analysis. For systems in which there is a giant planet interior to the HZ, which must have got there by migration, there are two cases considered: first, the case when the migration of the giant planet across the HZ has not ruled out the existence of an Earth-mass planet in the HZ; second, the case where it has. In the former case we have found that 60% of the 152 systems offer safe havens to Earth-mass planets across greater than 20% of the HZ width. We regard such systems as being habitable today. We have also estimated whether habitability is possible for 1000 Myr into the past (provided that this period post-dates the heavy bombardment of planets in the HZ). Of the 143 systems that are susceptible to this second analysis, we find that about 50% offer habitability sustained over 1000 Myr. If giant planets interior to the HZ rule Earth-mass planets, then 60% and 50% fall to 7% in both cases.
Oceanic hypervelocity impact events: a viable mechanism for successful panspermia?
- D.J. Milner, M.J. Burchell, J.A. Creighton, J. Parnell
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- 16 October 2006, pp. 261-267
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The idea that life migrates naturally between planetary bodies has grown in strength in recent years. This idea (panspermia) is believed to be possible via the mechanism of impact events. Previous research on this topic has concentrated on small meteoroids (micrometres to centimetres in diameter), with giant objects (metres to kilometres in diameter) being relatively ignored. This is due to the common belief that the larger objects vaporize on impact with the Earth's surface, which in most studies is taken as rock. Here we examine experimentally whether hypervelocity impacts into water result in significant survival of the impactors. For this study the University of Kent's two-stage light gas gun was used to accelerate millimetre-sized shale projectiles obliquely into a relatively deep water layer, at approximately 5 km s−1. Two shots have been made with surviving fragments being recovered from each. The surviving fragments appear highly shocked and display clear signs of cracking. The fragments that have been isolated contribute to a significant percentage (~10%) of the original unfired projectile mass and are as large as ~20% of the original projectile diameter. This indicates that oceanic hypervelocity impact events of large asteroids may deliver significant volumes of solid material to the Earth and thus provide a possible mechanism for successful panspermia.
Context for the ESA ExoMars rover: the Panoramic Camera (PanCam) instrument
- Andrew D. Griffiths, Andrew J. Coates, Ralf Jaumann, Harald Michaelis, Gerhard Paar, David Barnes, Jean-Luc Josset
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- 23 October 2006, pp. 269-275
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The recently approved ExoMars rover is the first element of the ESA Aurora programme and is scheduled to deliver the Pasteur exobiology payload to Mars by 2015. The 0.7 kg Panoramic Camera will provide multi-spectral stereo images with 65 ° field-of-view (1.1 mrad/pixel) and high-resolution (85 μrad/pixel) monoscopic ‘zoom’ images with 5 ° field-of-view. The stereo wide-angle cameras (WAC) are based on the Beagle 2 Stereo Camera System heritage (Griffiths et al. (2005). Planet. Space Sci. 53, 1466–1488). The Panoramic Camera instrument is designed to fulfil the digital terrain mapping requirements of the mission as well as to provide multi-spectral geological imaging, colour and stereo panoramic images, water vapour abundance and dust optical depth measurements. It can also be used for high-resolution imaging of inaccessible locations on crater walls and to observe retrieved subsurface samples before ingestion into the rest of the Pasteur payload.