ABC-NET Astrobiology Lecture Course Series (a.y. 2007-2008)

Astrobiology of Comets

F. Goesmann (MPS Lindau - Germany)

Biology outside earth is not as new a subject as one might think. From earliest times comets were considered relevant for life on earth and the state of theories developed form merely speculative to knowledge based. The most relevant effect of comets on earth is the delivery of matter, be it of organic nature, be it a constituent of the atmosphere. The aspects of this delivery will be elaborated with special emphasis on the current state of knowledge of cometary composition. Comets are not only a source of positive influence for terrestrial life but may also be a great danger to it. This aspect will only be a smaller part. The importance of missions to comets and especially their instrumentation will be outlined in a more extensive chapter. This is the area where the knowledge gain on comets is designed, built, and measured. In particular the Rosetta mission will be highlighted here. Finally, the less commonly accepted theories of biology of comets will be presented with the necessary caution. I think these theories are part of the discussion and students should be aware of their existence.

Astrobiology of Jupiter`s moon Europa

G. Tobie (University of Paris 12 - France)

The data returned by the Galileo spacecraft strongly suggest that a liquid water layer, several tens of kilometers thick, exist beneath the cold icy surface of Jupi-ter`s moon Europa. This internal ocean would be in contact with the inner silicate core, possibly volcanically active. Interestingly, the (P,T) conditions at the silicate-ocean boundary are quite similar to those existing on the Earth`s sea floor where organisms live without solar energy. The study of Europa is therefore essential to answer such as: does life exist everywhere water is present? Can life arise and develop in an environment where there is no sunlight ? What source of energy may be used by the microorganisms? The existence of an internal ocean is surprising since the satellite was expected to be fro-zen due to its very cold surface temperature (~100 K). For several years, tidal dissipation has been invoked to explain the possible presence of an ocean within Europa. Tidal dis-sipation comes from the viscoelastic response of the satellite to the 3.55-days tidal forc-ing. In the Laplace resonance, Io and Ganymede force the eccentricity of Europa. As it travels around Jupiter on an eccentric orbit, Europa is subjected to a periodical deforma-tion. Due to the viscoelastic properties of its materials, viscous dissipation by shear fric-tion occurs within each internal layer. Tidal dissipation in the inner core may heat up the outer silicate layer resulting in volcanism similar to the one observed on Io. Thermal evo-lution models indicate that the silicate core could have reached an highly dissipative state only if Europa experienced larger tidal forcing in the past. Future exploration of Europa is required to determine the exact depth of the liquid layer and to assess the possibility of seafloor silicate volcanism.

The lecture reviews our present knownledge on Europa: its geology and its internal struc-ture. Models of tidal dissipation and thermal evolution and their implications for the de-velopment of biogenic activity are presented. Concepts for future exploration missions toward Europa are summarized, with particular emphasis on the search for liquid water and on the exobiological potential of that `ocean` satellite.

Astrobiology of Saturn’s moons Titan and Enceladus

F. Raulin (University of Paris 12 - France)

Titan, largest satellite of Saturn, with a diameter of 5150 km, is the only satellite in the Solar System having a dense atmosphere. Since the discovery of the properties of this atmosphere, especially its main molecular composition – dinitrogen (N2) with a few percents of methane (CH4) – by the Voyager spacecraft observation in the early 80ties, Titan is considered as one of the most interesting bodies of the Solar System with regard to astrobiology. Indeed such an atmosphere is very favorable to the production of organic compounds as demonstrated by the Miller’s now historical experiment and the many similar experiments which were done later on. The likely presence of a complex organic chemistry in Titan’s atmosphere was also directly supported by the detection of many organic compounds detected by Voyager, and by several observations of Titan’s atmosphere from ground-based and Earth orbit telescopes. These discoveries were one of the main motivations of the scientific community for going back to the Saturn system with a very ambitious planetary mission: Cassini-Huygens. Most of our current knowl-edge of Titan is based on the new and very fresh observations done by Cassini-Huygens, coupled to laboratory experiments, including simulation experiments, and theoretical modeling (in particular photochemical models and ionospheric chemical models of the atmosphere, and models of the internal structure of the satellite). The lecture presents some historical data on Titan before Cassini-Huygens, before describing the Cassini-Huygens mission and its scientific payload. Then the models of formation and of internal structure of Titan are summarized and the general astrobiology of Titan is presented. Each of the three main astrobiological aspects - similarities with the Earth, organic chem-istry and habitability – are described. Among the several fully unexpected discoveries done by the Cassini-Huygens mission are the observations of important geological activi-ties on Enceladus, a smaller satellite of Saturn, with a radius of only 250 km. These ob-servations and their potential astrobiological input are briefly described. New concepts for future exploration missions of Titan and Enceladus are presented as a conclusion.

Astrobiology of Terrestrial Planets with em-phasis on Mars

M. Grady (Open University - Milton Keynes - UK)

Astrobiology of the terrestrial planets, with emphasis on Mars The four rocky planets of the inner Solar System are together referred to as the terrestrial planets. They differ in fundamental aspects such as size, atmosphere, magnetic field and surface temperature. Only one of the four is clearly the host to abundant life. Why is this? There are many features of Earth that make it suitable for life, but there is also much speculation about the potential for life to exist on Mars. Why is there so much interest in Mars? Many scientists believe that there is overwhelming evidence that suitable environmental conditions for life to survive existed on Mars in the past, when the planet had a thicker atmosphere and liquid water was stable at the Martian surface. Most of the observations in support of this belief come from missions to Mars, both orbiting satellites and landing craft. There is, however, another window on to the Martian surface, and the processes that take place there: meteorites from Mars. Martian meteorites are igneous rocks, some of which have suffered alteration by aqueous fluids at Mars` surface. Many Martian meteorites also contain pockets of gas trapped within impact-generated melt; the gas was trapped from the martian atmosphere during ejection of the meteorites from the surface of the planet. One of the Martian meteorites, ALH 84001, achieved notoriety after a team of NASA scientists identified structures within carbonates patches as fossilised Martian microfossils. Although their evidence is by no means conclusive, and not accepted by much of the scientific community, their findings have stimulated a great deal of interest in exploration of Mars for traces of past life. I will consider what we know about Mars, both from space missions and from Martian meteorites, and will also discuss results from recent space missions, and whether analyses carried out on the Martian surface show that the red planet is a dead planet - or whether it is alive!

Habitability in our Solar System and beyond

C. Cockell (Open University - Milton Keynes - UK)

What do we mean by ’habitability’? Habitability depends on the organisms that are considered and it is defined by the chemical and physical tolerances for a given organism. As we currently have no direct evidence for life on another planet, habitability is necessarily constrained by our knowledge of life on Earth. We use our knowledge of the extremes of life on Earth to assess extraterrestrial environments and the plausibility that they can support life. I will discuss the use and limitations of the concept of ’habitability’ and provide examples of how we assess the habitability of other worlds using organisms from extreme environments on Earth. I will discuss how considerations of energy availability (redox couples), the presence of water and carbon sources have shaped our view of the habitability of other planets and will eventually be used to assess the habitability of extrasolar planets. The formulation of a definition of ’habitability’ can greater assist us in defining the possibilities for life elsewhere.

Astrodynamics and Technology Aspects of Astrobiology Missions in our Solar System

S. Fasoulas (University of Dresden - Germany)

1) Launch: scenarios, Δv, launch windows; constraints for biological payloads.

2) Interplanetary trajectories: transfer trajectories; space environment; constraints for biological payloads.

3) (Re)Entry, Descent, Landing: entry in different atmospheres (CO2, CH4, …); problems to biological payloads.

4) Mission subsystems: energy system; thermal system; communication, data handling & transfer; interaction to biological payloads

5) Return-to-Earth Missions: possibilities; technical constraints to probes, ...

Paragraph 1 to 5 shall be summarised for astrobiology missions to planets (Mars), asteroids, comets and/or moons (Europa).

ESA Astrobiology Missions and Facilities within the HME Directorate

J. Vago (ESA/ESTEC - The Netherlands)

ExoMars’s scientific objectives are: 1) To search for signs of past and present life; 2) To identify surface hazards to future human missions; and 3) To characterise, in the shallow subsurface, the vertical distribution profile for water and geochemical composition. ExoMars will deploy a high-mobility rover on the Martian surface, carrying a comprehensive suite of analytical instruments dedicated to exobiology, geochemistry, and environmental research: the Pasteur payload. Over its planned 6-month lifetime, the rover will travel a few tens of kilometres searching for traces of past and present signs of life. It will do this by collecting and analysing samples from within surface rocks, and from underground - down to 2-m depth. The very powerful combination of mobility with the capability to access locations where organic molecules are well preserved is unique to this mission. Provided an appropriate landing site can be targeted, ExoMars will have the right tools to try to answer the question of whether life ever arose on the red planet. The ExoMars mission contains two other elements: a Mars orbiter and a Descent Module. The orbiter’s main task will be to act as data relay satellite, although it will also carry an important scientific payload. The Descent Module’s objective is to safely deliver to the Martian surface the ExoMars Rover. The rover, whose mass is presently estimated at 220 kg, will carry the Pasteur scientific payload. The Pasteur Payload is equipped with a multispectral, stereoscopic camera; an electromagnetic subsurface sounder to identify local water/ice deposits; a drill capable of reaching a depth of 2 m, and also of collecting specimens from within surface rocks; a sample preparation and distribution unit, an optical microscope; an oxidation sensor; and a variety of instruments for the characterisation of organic substances and minerals. Latitudinal bands between -15º and 45º can be targeted for landing, ensuring that the mission is flexible enough to accommodate interesting new sites based on latest available data from on-going Mars orbital missions. Over its envisioned lifetime of 180 sols, the rover is designed to cover 10+ km of ground track over typical Martian terrain. Operations beyond this period will depend mainly on the amount of dust deposited on the rover’s solar panels.

Extremophiles, the Physico-Chemical Limits of Life (Growth and Survival)

H. Stan-Lotter (University of Salzburg - Austria)

Extreme environments are characterized by physical and chemical parameters which were considered lying outside the range which is suitable for life. In recent years, the notion of what constitutes life-limiting conditions in an environment has undergone dramatic changes: microorganisms and occasionally higher organisms were discovered, which not only tolerate, but thrive under ranges of temperatures, pH values, pressures, salinity, ionizing radiation etc. previously thought to destruct biomolecules and organ-isms. Some of the mechanisms responsible for these life styles are in the process of being elucidated. The presence of liquid water is a prerequisite for growth under all kinds of conditions; however, survival of resting stages, such as spores or dormant forms, was shown to occur in vacuum and in space conditions for several months. The detection of numerous viable prokaryotes and spores in subterranean locations, such as basalt, gran-ite, ancient halite and sediments, suggests the possibility of extensive longevity, perhaps over millions of years. The implications of these discoveries for the search for extraterrestrial life are several-fold: the probability of finding prokaryotic life in environments such as the subsurface of Mars or the salty ocean of the Jovian moon Europa appears greatly enhanced, and the potential for panspermia is considered more plausible than ever before.

Hunting Protein Ancestors

F. Ferrari (University of Szcecin - Poland)

In searching the origin of life it is possible to apply two different approaches. The first one is a down-to-top approach, in which, starting from inanimated matter, like for instance basic organic compounds or aminoacids, one tries to reproduce the processes and the conditions that gave birth to the first living beings about 3.85 Ga ago. Alterna-tively, one may attempt to extract hints about the first steps of the evolution of life from the observation of present organisms. This top-down approach is based on the fact that all living forms have a common ancestor, so that it is licit to assume that some of its ves-tiges are still preserved inside the genetic code of current cells and bacteria. Indeed, it is well known that there are structures inside proteins, like structural motifs and folds, which seem to be intimately connected with evolution. For example, while there are about 100,000 expressed proteins in eukariotic systems, there are much fewer motifs and folds, a fact that is related to the pathways of evolution. In this lecture some aspects of the top-down approach will be illustrated. After a brief review of the known structures in proteins and other macromolecules which are relevant for life, a discussion will follow about the physical and chemical properties of biopolymers. Physical and chemical laws were in fact present during the period in which life started on the Earth and have cer-tainly put constraints on the formation of the earliest biopolymers. Therefore, they can be exploited in order to guess how the genome of the most primitive organisms looked like. The information about the general characteristics of ancient life forms obtained using physical and chemical arguments may be used in the search of the remnants of the first genes which could be inside modern genes for instance due to processes of gene fusion. The lecture will end up with a discussion about the physical experimental methods that allow the detection of possible substructures inside biopolymers like proteins or DNA.

Role of Catalysis on Synthesis of Biomolecules

R. Saladino (University of Viterbo - Italy)

Prebiotic chemistry plays a central role in the investigation of the possible scenarios of the early chemical environments. Its goal is to shed light on the events involved in the synthesis of initial biomolecules and on the self-organization processes that led the last common ancestor. Even though a well defined scenario for the physico-chemical conditions on the primitive Earth is not available, one can assume that a synthetic path-way, in order to be considered prebiotic, should use the simplest chemicals and the most common conditions present at that time. Low molecular weight molecules such as car-bon dioxide, hydrogen cyanide, formamide and formaldehyde, easily formed from the primitive atmosphere by ultraviolet light, heat or electric discharge as energy sources, have been considered as prebiotic precursors. The catalysis played a crucial role in the prebiotic synthesis of biomolecules starting from these chemical precursors. Several minerals and metal oxides characterized by chemical, redox and photochemical catalytic properties were widely diffused on the primitive Earth. These compounds, when compo-nents of a reaction mixture, could have enhanced the efficacy of prebiotic syntheses, af-fecting the selectivities of the reactions and furnishing local microenvironments able ei-ther to concentrate dilute reagents or to preserve newly formed biomolecules from de-gradative processes. In this lecture we will focus on the main concepts of catalysis ap-plied to prebiotic chemistry, including homogeneous and heterogeneous catalysis, multi-functional catalysis and autocatalysis. Different examples on the role of catalysis in the synthesis of biomolecules starting from simple precursors will be discussed with a spe-cial attention to the synthesis of sugars, peptides and oligonucleotides. Examples of pre-biotic synthesis of biomolecules with non terrestrial minerals as well as multi-components catalysis will be also described.

From Molecular Evolution to Cellular Life

K. Lehto (University of Turku - Finland)

First, the essential features of cellular life will be considered; what is required for life, and what are the criteria of life. Nucleic acids, genetic code and its expression system are conserved and ubiquitous properties of all life forms, and therefore are assumed to be the most original functional units of life. Molecular analysis of these structures gives suggestions of how they may have been involved in the early molecular evolution, and what functions they may have provided to the early (precellular) replicators. By going backwards, step by step, one sees which inventions had to precede each stage of early evolution: genetically encoded proteins had to exist prior to the establishment of the Last Universal Common Ancestor (LUCA), and RNA-mediated RNA-replication, or so called RNA world, had to predate genetically encoded proteins. Some cellular RNA-molecules, which have different enzymatic activities and are highly conserved between different organisms are supposed to be relicts from this era. Still, many questions related to the early molecular evolution remain open. We do not know, for instance, the prebiotic synthesis routes for the nucleotides, how life chose to use the distinct nucleotides and amino acids in their distinct chiralic forms, how the first functional polynucleotides were assembled, or how the earliest life forms were confined.

Basic Prebiotic Chemistry

H. Cottin (University of Paris 12 - France)

Before life could arise on a planet, atoms have to organise themselves into complex biological molecules such as proteins, RNA, or DNA. Such elaborated structures can’t appear by themselves at once, they result from a complex chemical evolution, starting with the simplest organic compounds. At some point, at some yet to define stage of complexity and organisation of matter, an important step is made and chemistry turns into biology.

This lecture is devoted to the study of prebiotic chemistry; it focuses on the very first steps of the chemical evolution: the synthesis of the building blocks of the molecular engine of any known living organism on Earth. In a previous lecture of this series, how atoms form in stars was explained. Now we consider how atoms can spontaneously com-bine to make molecules, before discussing the molecular evolution to cellular life in the next lecture.

In the first part of this lecture living systems are dismantled into more elemental frag-ments: organic molecules. To address the origin of life, the next question would be how those fragments can be synthesized in an abiotic manner. After a short historical review about the chemistry of life different tracks are explored: an endogenous production of the molecules of life, within the Earth atmosphere or in the depths of primitive oceans, or an exogenous source of prebiotic molecules through space delivery via meteorites and com-ets. The chemical pathways of synthesis of the building blocks of life will then be de-scribed.

Planet Formation

E. Szuszkiewicz (University of Szczecin - Poland)

The most natural environment for the existence of life and its development is a planet orbiting a star. We have only one, but extremely good example for that, namely the planet Earth circling around the Sun. There are quite a few conditions which need to be satisfied for life to be present on our planet and this will be the subject of a separate lecture. Here, we would like to focus on the more basic question of how planetary sys-tems form and evolve. We adopt a methodology which proved itself to be powerful and successful in the field of stellar evolution, which means, we make use of the fact that there are many stars with their planetary systems in the sky in different stages of their evolution. By observing them and building models we can reconstruct the time sequence and find out the most plausible scenarios for planet formation. Our methodology is justi-fied, because we know already more than 200 mature, fully developed planetary systems and numerous examples of protoplanetary discs, which are believed to be the sites where planets are born. During this lecture we review the life history of our planetary system. We will admire how our present Solar System has been born, starting from the molecular cloud collapse, after passing through a deeply embedded protostellar phase and succes-sively through a T Tauri phase. Next, we will watch how planetesimals and protoplanets form in protoplanetary discs via sedimentation and agglomeration until the final system arises after 4.6 mld years of its evolution. The Hubble Space Telescope, the Spitzer Space Telescope, the James Clerk Maxwell Telescope, among other missions and in-struments, helped us to put together the different stages of this scenario. Advanced nu-merical simulations promise an even more detailed story, as they predict precisely the robust features in the structures of protoplanetary discs and the architectures of planetary systems. These predictions will be verified by present and future observatories like COROT (COnvection, ROtation and planetary Transits), Herschel, ALMA (Atacama Large Millimetre/Submillimetre Array), James Webb Space Telescope, Kepler and a few others. At the end of this lecture we consider briefly also what will happen with a planetary system, like our own, during further evolution of the central star, when the star enters a Red Giant phase and finally become a white dwarf.

From Big Bang to the Molecules of Life

H. Lehto (University of Turku - Finland)

Evolution of the universe predates both the chemical evolution and the evolution of life. We will summarise the origin of the critical elements for life, the CHNOPS, and the initial formation of molecules. From cosmological models we can understand the origin of hydrogen and helium. Later hydrogen will be required when water is formed. Helium, which appears quite useless for life, turns out to be a critical factor in the synthesis of carbon leading to heavier elements. The second compound of water, oxygen, is formed in the hot cores of stars. Once these elements get from the stars back into the cool interstellar space they begin forming interstellar clouds, where a vast spectrum of mole-cules is formed. The observed properties of these molecules, and the larger dust particles will be reviewed. These will the play an important role in the formation of planets in the accretion disks of a metal rich population of stars. This material reprocessed by the newly formed star and other planets “rains” on the young planet in the form of meteorites, comets and asteroids creating a supply of raw materials needed for the prebiotic evolution and the eventual biological evolution of life.

Short Introduction into Astrobiology

A. Brack (University of Turku - Finland)