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.

Over the last three years an outreach programme in astrobiology has been stimulating public interest in South Wales, UK. To date, 550 people have attended an accredited undergraduate course in astrobiology, Alien Worlds. Funded by a European Social Fund grant, this modular course has introduced students to the multidisciplinary nature of astrobiology, coupling academic content to a practical ability to recognise the constellations and objects of the night sky. This paper outlines the course's background, content, delivery and outcomes as an example of the outreach potential of the science and culture of astrobiology.

Spectroscopic investigations of surface mineral components, expected to exist on the surface of Mars, using multiple spectral ranges and techniques, are vital to obtain the ground truth information or reference data for Mars exploration missions. This paper presents visible, near-infrared, thermal infrared reflectance and thermal infrared transmission spectra, as well as X-ray diffraction and scanning electron microscope/energy dispersive X-ray analyses of salt crusts and sediments interleaved with cyanobacterial materials from a coastal zone of the United Arab Emirates, where sabkhas exist. The samples obtained from sabkhas were characterized because they contain minerals requiring the water for formation and they provide a possible environment for some of the earliest organisms on Earth. The surface minerals identified include gypsum, calcite, halite, aragonite and dolomite. These sediments were found to be mixed with each other and intermingled with an algal mat, which consisted of cyanobacteria. If such materials formed in similar environments on Mars, their identification would be important for understanding the geobiological conditions of the planet and the potential habitability for life.

This project researched the possibility of photosynthetic life on Mars. Cyanobacteria were used as potential analogs and were subjected to various Martian-simulated conditions. Synechocystis sp. PCC 6803 was exposed to low pressure, ultraviolet radiation and Martian-simulated atmospheric composition, and proved resistant to the combination of these stresses. However, this organism could neither grow within Martian Regolith Simulant, owing to the lack of soluble nitrogen, nor could it grow in cold temperatures. As a result, later research focused on psychrotolerant cyanobacteria capable of utilizing atmospheric nitrogen. These Antarctic nitrogen-fixing strains were able to grow in Martian Regolith Simulant at temperatures as low as 4 °C. In addition, they proved resistant to salinity, ultraviolet radiation and freeze/thaw conditions. These results suggest that Antarctic nitrogen-fixing cyanobacteria are good analogs for potential Martian life and should be considered in future exploratory missions for life on the red planet.

One of the criteria for the concept of a galactic habitable zone (GHZ) is that the pattern speed of the stars in the GHZ should be close to the pattern speed of the spiral arms. Another criteria is that the stars in it should have a high enough metallicity. In a barred galaxy, the GHZ will be more complicated to define since the bar can change stellar orbits. Many disc galaxies, including the Milky Way, are barred galaxies. The stars in the bar move in a number of fairly complicated orbits. However, the bar will also influence the orbits of stars in the whole galaxy. Stars passing close to the bar can either gain or lose angular momentum, due to a positive or negative torque by the bar. Some stars will therefore be captured by the bar while some stars eventually may reach the escape velocity from the galaxy. The bar will hence be able to relocate stars, and stars with low or high metallicity could be found far away from their original orbits. The ordinary evolution of a bar is to grow in length out to the co-rotation radius for the pattern speed of the bar. As the galaxy ages, and the bar grows in length, the bar will influence a larger part of the galaxy. The effect of moving stars inwards or outwards is greatest just outside the bar, and this region can eventually lose a high percentage of the stars.

New observations of Titan by the Cassini spacecraft suggest the presence of cryovolcanism on the surface. Cryovolcanism has important astrobiological implications, as it provides a means of exposing Titan's organics to liquid water, transforming hydrocarbons and nitriles into more evolved and oxidized prebiotic species. One possible cryovolcano – the 180 km structure Ganesa Macula – resembles the pancake domes seen on Venus by the Magellan spacecraft. To assess the potential of Ganesa Macula for prebiotic chemistry, we estimate its height using radarclinometry and other methods, and calculate the freezing timescale assuming an initially completely liquid dome. Given height constraints of ~200 m to 4 km, we find that liquid water or water–ammonia environments could be sustained in Ganesa Macula for timescales of the order of 102–105 years. These timescales open a window for prebiotic chemistry far wider than can be explored in terrestrial laboratory experiments.

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.

EANA–European Astrobiology Network Association

10–12 October 2005

Budapest, Hungary

The large-moon hypothesis states that planetary habitability is enhanced by the presence of a large satellite. This controversial proposal is linked to the equally controversial idea that the axial stability of a planet also enhances habitability. Previous work has shown that, far from encouraging axial stability, large moons actually destabilize obliquity when the effects of tidal drag on the planetary spin rate are taken into account. However, our Moon's mass is remarkably close to the upper limit allowed by axial stability, suggesting that the large-moon hypothesis is actually correct but constrained by an independent requirement for axial stability. This conclusion can be tested by looking at the typical separations between large exo-planets because axial stability is more likely in planetary systems with widely spaced gas giants. Thus, if axial stability really does enhance habitability, Jupiter and Saturn should be unusually widely spaced. This can be tested using data expected from gravitational microlensing planet-search surveys. Unfortunately, in the event of a negative result from this test, it is not possible to distinguish whether this results from large moons and stable axes being unimportant for life or results from large moons and stable axes being widespread.

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.

The recognition and understanding of the early fossil record on Earth is vital to the success of missions searching for life on other planets. Despite this, the evidence for life on Earth before ~3.0 Ga remains controversial. The discovery of new windows of preservation in the rock record more than 3.0 Ga would therefore be helpful to enhance our understanding of the context for the earliest life on Earth. Here we report one such discovery, a ~3.4 Ga sandstone at the base of the Strelley Pool Formation from the Pilbara of Western Australia, in which micrometre-sized tubular structures preserve putative evidence of biogenicity. Detailed geological mapping and petrography reveals the depositional and early diagenetic history of the host sandstone. We demonstrate that the depositional environment was conducive to life and that sandstone clasts containing putative biological structures can be protected from later metamorphic events, preserving earlier biological signals. We conclude from this that sandstones have an exciting taphonomic potential both on early Earth and beyond.

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.

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.

The response of organic matter to high-temperature events is important to astrobiology, as it governs the survival of carbon during several processes that may be critical to the origin and spread of life. Impact cratering is a widespread high-temperature process. The behaviour of carbon during impact events is not well understood. But there is the potential to examine other examples of the response of organic matter to high-temperature processes in the terrestrial geological record. In this study, we report on the interaction of Tertiary igneous intrusions (dolerite sills) and carbon-rich Jurassic mudrocks on the Isle of Skye, Scotland. Despite the high temperatures of the igneous intrusion, carbon has been preserved at the dolerite–shale contact and in shale enclaves where partial melting of the shale has occurred. Even though the temperatures achieved by igneous intrusion are much lower than during impact events, it is a valuable analogue, because it represents a rapid introduction of high temperatures to a carbon-rich rock.

The discovery of icy bodies in our Solar System has opened up the possibility that life may exist on and below their surfaces. Snow and ice are good sites for the preservation of biomarkers as they trap and preserve organic matter that is deposited onto their surfaces. Terrestrial samples of snow and ice collected from Ben Macdui in north east Scotland have been analysed for organic compounds contained within them. A range of n-alkanes and n-alkanoic acids were found in both samples. The particulate matter contained proportionally more higher weight n-alkanols than the melted water. This is because higher molecular weight molecules are less soluble in water. Therefore, the volume of snow and ice to be sampled on other icy bodies is an important factor, as many important biomarkers have high molecular weights and may not be detected in small quantities of melted water.

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.