Marina Resendes de Sousa António

A Two-Tiered Approach to Assessing the Habitability of Exoplanets

In the next few years, the number of catalogued exoplanets will be counted in the thousands. This will vastly expand the number of potentially habitable worlds and lead to a systematic assessment of their astrobiological potential. Here, we suggest a two-tiered classification scheme of exoplanet habitability. The first tier consists of an Earth Similarity Index (ESI), which allows worlds to be screened with regard to their similarity to Earth, the only known inhabited planet at this time. The ESI is based on data available or potentially available for most exoplanets such as mass, radius, and temperature. For the second tier of the classification scheme we propose a Planetary Habitability Index (PHI) based on the presence of a stable substrate, available energy, appropriate chemistry, and the potential for holding a liquid solvent. The PHI has been designed to minimize the biased search for life as we know it and to take into account life that might exist under more exotic conditions. As such, the PHI requires more detailed knowledge than is available for any exoplanet at this time. However, future missions such as the Terrestrial Planet Finder will collect this information and advance the PHI. Both indices are formulated in a way that enables their values to be updated as technology and our knowledge about habitable planets, moons, and life advances. Applying the proposed metrics to bodies within our Solar System for comparison reveals two planets in the Gliese 581 system, GJ 581 c and d, with an ESI comparable to that of Mars and a PHI between that of Europa and Enceladus.

Pavilion Lake Microbialites: Morphological, Molecular and Biochemical Evidence for a Cold-Water Transition to Colonial Aggregates

The presence of microbialite structures in a freshwater, dimictic mid-latitude lake and their establishment after the last ice age about 10,000 years ago is puzzling. Freshwater calcite microbialites at Pavilion Lake, British Columbia, Canada, consist of a complex community of microorganisms that collectively form large, ordered structured aggregates. This distinctive assemblage of freshwater calcite microbialites was studied through standard microbial methods, morphological observations, phospholipid fatty acid (PLFA) analysis, DNA sequencing and the identification of quorum sensing molecules. Our results suggest that the microbialites may represent a transitional form from the exclusively prokaryotic colonial precursors of stromatolites to the multicellular organismic aggregates that give rise to coral reefs.

The power of social structure: how we became an intelligent lineage

New findings pertinent to the human lineage origin ( Ardipithecus ramidus ) prompt a new analysis of the extrapolation of the social behavior of our closest relatives, the great apes, into human ‘natural social behavior’. With the new findings it becomes clear that human ancestors had very divergent social arrangements from the ones we observe today in our closest genetic relatives. The social structure of chimpanzees and gorillas is characterized by male competition. Aggression and the instigation of fear are common place. The morphology of A. ramidus points in the direction of a social system characterized by female-choice instead of male–male competition. This system tends to be characterized by reduced aggression levels, leading to more stable arrangements. It is postulated here that the social stability with accompanying group cohesion propitiated by this setting is favorable to the investment in more complex behaviors, the development of innovative approaches to solve familiar problems, an increase in exploratory behavior, and eventually higher intelligence and the use of sophisticated tools and technology. The concentration of research efforts into the study of social animals with similar social systems (e.g., New World social monkeys (Callitrichidae ), social canids ( Canidae ) and social rodents ( Rodentia )) are likely to provide new insights into the understanding of what factors determined our evolution into an intelligent species capable of advanced technology.

A Dynamic Scheme to Assess Habitability of Exoplanets

In the next few years, the number of catalogued exoplanets will be counted in the thousands and with it the need will arise to prioritize them in regard to habitability and the potential presence of life. Here, we suggest a first attempt of a dynamic scheme for classification based on our current understanding of parameters that are consistent and beneficial for the presence of life. These parameters include the presence of (1) a terrestrial planet or moon, which (2) is endowed with a significant atmosphere; the presence of (3) a magnetic field enveloping the exoplanet; (4) internal differentiation and plate tectonics; (5) detectable surface liquids, preferably water, on the surface of the planetary body; and (6) the detection of geoindicators; and (7) bioindicators. We propose to calculate a habitability index (HI) based on these parameters, but realize the assumptions that go into this value and the very bias introduced by the limitations of the detection methods. However, in order to account for the assumptions and limitations of this method, the HI index is an open scheme that can be updated as technology and our knowledge about habitable planets advances.