NORDITA

Astrobiology is a new and dynamic topic, which covers many subfields within astronomy and touches upon areas where astronomy interfaces with biology, biochemistry, geology, biophysics and geophysics. Finland founded a national astrobiology network earlier this year and Sweden formed one the year before. The European Exo/Astrobiology Network Association (EANA) was founded in 2000. Currently we are getting involved in forming an astrobiology research training network, under the EU's 6th framework program. Having a Nordic network may strengthen our position in this effort both nationally and internationally. It may also serve as a starting point for a proposal to NorFA for a Nordic Network. The timeliness of a possible Nordic Project proposal to Nordita is also indicated by the fact that the national astrobiology networks in Sweden and Finland have only been initiated recently, and that there will even be an international bioastronomy meeting in Iceland next year, and there is currently a proposal to NorFA (PI: Birgitta Nordström) for a Summer School on astrobiology. Also, over 100 planetary systems have been found since 1995, providing a much better chance of understanding planet formation both within and outside the possible habitable zone. Finally, the astrophysics group at Nordita is very interested in this topic and would like to start up collaborations within the topic.

Astrobiology is interdisciplinary, and there exists relevant expertise in various subfields, but in order to make a contribution to the field we need to bring the expertise from different subfields together. Something like 2 meetings per year for 2-3 days with talks and room for discussions can be very useful. Experience shows that some new collaborations will naturally emerges from such activity -- even if this happens years after the duration of the project.

In preliminary discussions we have begun to isolate a few fields of interest. There is no need to restrict the list to these topics; some may be obsolete and others can be proposed instead. This list is not meant to reflect our existing level of experience around this topic. Instead, it is meant to reflect topics that are not just remotely connected with Astrobiology, but that are clearly relevant, exciting, and hopefully feasible.

In broad terms, we have in mind questions relevant to the origin of life and to the possible existence of life elsewhere in the universe.

(i) What controls the habitability of other planets and exoplanets or their satellites? How does one go about modelling the evolution of their atmospheres and possibly their oceans, how does the atmospheric composition and gas content change with time? How important are volcanic activity and plate tectonics? How can we predict these for bodies of other planetary systems?

(ii) What is the relevance of impacts from meteors and comets. What is the effect on the origin and evolution of species? How do we model impacts? How and where do comets or meteorites break up, and how do dust and possibly living cells evolve in the atmosphere? Can we predict the induced climatic changes? What are the effects on the ecosystems?

(iii) Do we understand the evolutionary mechanisms of life? What is known about growing life from scratch? What are the involved timescales on Earth and elsewhere, and how can this be modelled?

(iv) Can we recognize signatures of life on other worlds? Do we know which signatures to look for?

In general, the possibility of modelling and prediction making hinges on the availability of hard tests. The field is just so broad and complex that not all the facts may be known to everybody, so getting interested people together is a necessary first step.

PHYSICS

One research area focuses on formation and depletion mechanisms of organic molecules in extraterrestrial environments, where the build-up of complex molecules can proceed on grain surfaces or through gas phase reactions. The latter often involves ion-neutral reactions with subsequent dissociative recombination. Dissociative recombination is studied at the CRYRING heavy ion storage ring at the Manne Siegbahn Laboratory in Stockholm. The obtained results can be used for improving chemical models of molecular clouds and planetary atmospheres. With the recent discovery of anions in dense molecular clouds, environments may exist where they could cause mutual neutralization. The efficiency of these reactions will be studied at the Double Electrostatic Ion Ring Experiment (DESIREE), currently under construction at Stockholm University. An interesting astrobiological question is to what extent biomolecules and their precursors can evolve in the interstellar medium.

Another line of study is of the survival of biomolecules during atmospheric entry. Organic molecules have been found in interplanetary dust particles (IDPs), which frequently impact the Earth. It is of astrobiological interest to investigate how life-related molecules interact with the atmosphere, and if sublimable phases, e.g. water, can help protect them during entry. These experiments are carried out using an electrospray ion source.

>> Stockholm University Department of Physics

GEOLOGICAL SCIENCES

The research at the Department of Geological Sciences concerns the formation of organic molecules in terrestrial environments and the effects of life on Earth's chemistry. In one project, the abiotic (Fischer-Tropsch) synthesis of organic molecules under hydrothermal conditions, which is suggested to play an important role in the abiotic formation of hydrocarbons, is investigated. Experimental simulations of hydrothermal environments will increase the understanding of mechanisms and pathways for the formation of organic molecules on Earth and in the Solar System.

Another project examines the serpentinization process under specific conditions, to broaden the knowledge of a process that is found on Earth and in meteorites. Serpentinization requires water and is heat releasing, which is of special interest in cold environments. The process is suggested to release enough energy to be self-sustained in meteoritic parent bodies.

The dynamics of methane under various conditions is also studied, using laboratory experiments in combination with thermodynamical modelling. A dead planet would have an atmosphere in abiological steady state equilibrium. But Earth's atmosphere has incompatible gases, e.g. methane and oxygen, which coexist in disequilibrium. The persistence of this state suggests the existence of an of an active control system, and thus reveals the presence of life. On a world of carbon-based life, the recorded geological evidence show that the unregulated injection of methane to the atmosphere has changed from early history of Earth up to now. The Gaia hypothesis suggests that life is an active participant in shaping the environment on which it de- pends. These changes leads to the question of how the dynamics of methane relates to the origin of life.

The research is affiliated with the activities of the Deep Carbon Observatory (DCO) - Deep Energy Directorate

>> Stockholm University Department of Geological Sciences

MOLECULAR BIOLOGY AND FUNCTIONAL GENOMICS

Astrobiological research at the Department of Molecular Biology and Functional Genomics focuses on two important aspects of early life on Earth.

Using both experimental molecular as well as computational techniques, ribonucleotide reductases (RNR) - an enzyme family that is crucial for the synthesis of the building blocks of DNA - are studied. RNR catalyzes the reaction that provides DNA-precursors in all cells, and thereby also regulates cellular replication and proliferation. RNRs come in three major classes and within and between those classes exhibit a significant level of sequence divergence, making standard techniques for the study of their origin and evolution hard to apply. By reconstructing and synthesizing ancestral RNRs, light can hopefully be shed on this question. Additionally, characterization and comparison of insertion sites of self-splicing elements can give clues to why RNR genes are such frequent hosts for them, and their potential role in the horizontal transfer of RNR genes between organisms.

The departments second interest lies within the field of early genome organization and evolution, where the possible structure of the Last Universal Common Ancestor (LUCA) of modern life (i.e. Bacteria, Archaea and Eukaryotes) is investigated. Particularly interesting questions involve the origin of messenger RNA, the bridge between a hypothetical ancient RNA world and modern DNA-Protein life.

>> Stockholm University Department of Molecular Biology and Functional Genomics

ASTRONOMY

At Stockholm Observatory, imaging investigations of the physical structures of circumstellar disks, primarily debris disks, are carried out using telescopes in the optical, far-infrared, and sub-mm wavelength regions, in order to better determine how disks evolve with time, and find similarities to our own Solar system. Sub-mm observations with LABOCA on APEX has been used to study a number of main-sequence stars with known ages and inferred disks (from mid- to far-infrared excess) at 870 µm, to probe extended, cold dust components (out to some hundreds of AU), in order to assess the existence, extent and mass of Kuiper-Belt-like disk structures. Together with the fairly accurately known ages of the stars, evolutionary aspects of the disks can be studied. In another project, properties of circumstellar dust disks are examined with a polarizing coronagraph instrument, where the direct light from the star is blocked out, making the faint scattered optical light from the disk detectable. By inserting a polarizing filter in different orientations, the angle and degree of polarization can be calculated and used to further enhance the contrast. This high-contrast imaging of low surface-brightness features can reveal gaps, knots, and asymmetries in the disks, perhaps indicating planets.

In addition to observational projects, theoretical studies and simulations of disks are carried out at the department.

>> Stockholm University Astronomy Department