The habitability of the Universe through 13 billion years of cosmic time

The field of astrobiology has made tremendous progress in modelling galactic-scale habitable zones which offer a stable environment for life to form and evolve in complexity. Recently, this idea has been extended to cosmological scales by studies modelling the habitability of the local Universe in its entirety (e.g. Dayal et al. 2015; Li & Zhang 2015). However, all of these studies have solely focused on estimating the potentially detrimental effects of either Type II supernovae (SNII) or Gamma Ray Bursts (GRBs), ignoring the contributions from Type Ia supernovae (SNIa) and active galactic nuclei (AGN). In this study we follow two different approaches, based on (i) the amplitude of deleterious radiation and (ii) the total planet-hosting volume irradiated by deleterious radiation. We simultaneously track the contributions from the key astrophysical sources (SNII, SNIa, AGN and GRBs) for the entire Universe, for both scenarios, to determine its habitability through 13.8 billion years of cosmic time. We find that SNII dominate the total radiation budget and the volume irradiated by deleterious radiation at any cosmic epoch closely followed by SNIa (that contribute half as much as SNII), with GRBs and AGN making up a negligible portion (<1%). Secondly, as a result of the total mass in stars (or the total number of planets) slowly building-up with time and the total deleterious radiation density, and volume affected, falling-off after the first 3 billion years, we find that the Universe has steadily increased in habitability through cosmic time. We find that, depending on the exact model assumptions, the Universe is 2.5 to 20 times more habitable today compared to when life first appeared on the Earth 4 billion years ago. We find that this increase in habitability will persist until the final stars die out over the next hundreds of billions of years.Comment: Under refereeing in Ap

An ESA roadmap for geobiology in space exploration

This work was supported by the European Space Agency under the Topical Team, 'Geobiology in Space Exploration'. Claire Cousins is funded by a Royal Society of Edinburgh Research Fellowship, co-funded by the Marie Curie Actions FP7 Programme.Geobiology, and in particular mineral-microbe interactions, has a significant role to play in current and future space exploration. This includes the search for biosignatures in extraterrestrial environments, and the human exploration of space. Microorganisms can be exploited to advance such exploration, such as through biomining, maintenance of life-support systems, and testing of life-detection instrumentation. In view of these potential applications, a European Space Agency (ESA) Topical Team “Geobiology in Space Exploration” was developed to explore these applications, and identify research avenues to be investigated to support this endeavour. Through community workshops, a roadmap was produced, with which to define future research directions via a set of 15 recommendations spanning three key areas: Science, Technology, and Community. These roadmap recommendations identify the need for research into: (1) New terrestrial space-analogue environments; (2) Community level microbial-mineral interactions; (3) Response of biofilms to the space environment; (4) Enzymatic and biochemical mineral interaction; (5) Technical refinement of instrumentation for space-based microbiology experiments, including precursor flight tests; (6) Integration of existing ground-based planetary simulation facilities; (7) Integration of fieldsite biogeography with laboratory- and field-based research; (8) Modification of existing planetary instruments for new geobiological investigations; (9) Development of in situ sample preparation techniques; (10) Miniaturisation of existing analytical methods, such as DNA sequencing technology; (11) New sensor technology to analyse chemical interaction in small volume samples; (12) Development of reusable Lunar and Near Earth Object experimental platforms; (13) Utility of Earth-based research to enable the realistic pursuit of extraterrestrial biosignatures; (14) Terrestrial benefits and technological spin-off from existing and future space-based geobiology investigations; and (15) New communication avenues between space agencies and terrestrial research organisations to enable this impact to be developed.PostprintPeer reviewe

The Water Activity of Mars-relevant Multicomponent Brines: The Changing Influence of Perchlorate on Habitability over Time

Low water activity limits the habitability of aqueous environments, and salts present on Mars are known to reduce water activity. As environmental brines are not pure solutions of a single salt, predicting their water activity is difficult without direct measurement. Martian brines are likely complex and dominated by ions including sulfates and perchlorates, unlike typical terrestrial aqueous environments dominated by sodium chloride. We used the Pitzer model to predict the water activity of multicomponent brines and tested against laboratory-produced brines, including for the first time perchlorate salts that are known to exist on Mars. Our calculations match measurements of single-salt solutions and predict the water activity of multicomponent brines with an accuracy dependent on the quality of thermodynamic data available for a given ion combination. We tested the hypothesis that some salts will dominate the water activity, and therefore habitability, of multicomponent brines. Some salts, such as sodium and magnesium sulfates, did not strongly modulate the water activity of the solution, whereas others such as magnesium chloride and some perchlorates did. Applied to the history of Mars, the data suggest that sulfates and sodium chloride present in Noachian and early Hesperian environments would not have limited habitability. Perchlorates produced photochemically later in the Amazonian could impose a water activity limit at high concentrations that is not significantly changed by other salts. Overall we found that magnesium and calcium chlorides mixed with perchlorates can reach the lowest water activity values and therefore the lowest habitability of the brines tested