Biosignatures in the solar system

Humanity's interest in whether or not we are alone in the universe spans generations, from Giordano Bruno's 16th century musings on other worlds and Giovanni Schiaparelli reporting seeing ‘canali’ in 1877 on the surface of Mars (which were thought to have been created by intelligent life) to alien invasions portrayed in today's movies. However, it is still unclear if other planetary bodies are capable of supporting life. In the search for life there are two broad areas we look into, the requirements of life and actual signs of life. The identification of the key requirements for life enables scientists to focus life detection efforts onto planets and satellites that are considered habitable and more likely to support life. However, our ability to find life or detect signs of life is based on our understanding of life on Earth

Thermochemical modelling of the subsurface environment on Enceladus

The subsurface environment of Enceladus is potentially habitable: there is a global subsurface ocean [1], energy from hydrothermal activity [2] and bioesential elements [3]. Carbon, as a fundamental bioessential element, it is critical for life, so understanding how it is processed within the Enceldus environment is crucial in assessing Enceladus’ potential habitability. Carbon is likely to be bound within the silicate interior [4] and liberated through water-rock (silicateocean) interactions. We have undertaken thermochemical modelling (CHIMXPT) [5] of these interactions and tested different hypotheses for the formation of Enceladus. Both models reacted the silicate interior (with a CI chondrite compositon [6]) with a fluid representative of the subsurface ocean: a) a dilute sodium chloride solution, based upon the assumption that the subsurface ocean originated as almost pure water [7]; b) a solution with a cometary composition based upon data collected from 67P [8], based upon the assumption that the water originated from melted cometary ice [9]. We have explored the full temperature and pressure ranges anticipated at the rock-water interface [2]. We will present the outcomes from this modelling, which includes a theoretical compostion for a modern day subsurface ocean, potential carbon cycling pathways and the effect of carbon species on the pH of the subsurface ocean fluid. [1] Thomas P. C. et al., (2016), Icarus, 264, 37-47 [2] Hsu H. W. et al., (2015), Nature, 519, 207-210 [3] McKay, C. P. et al., (2014) Astro-biology, 14, 352-355 [4] Glein C. R. & Waite J. H., (2020), Geophys Res Let, 47 [5] Reed, M. H., Spycher, N. F., Palandri, J., (2010) User guide for CHIM-XPT, University of Oregon, Oregon [6] Hamp R. E. et al., (2019), 50th LPSC 2019, Abstract 1091 [7] Brown R. H. et al, (2006) Science, 311, 1425-1428 [8] Hertier K. H., et al., (2017) RAS monthly notices, 469 [9] Neveu, M., et al., (2017) Geochim et Cosmochim, 212, 324-37

Modelling Water-Rock Interactions in the Sub-surface Environment of Enceladus.

Understanding the geochemical cycles occurring at the water-rock interface on Enceladus is crucial for establishing the potential habitability of the subsurface environment. Using data collected by the Cassini spacecraft (2005-2017) and estimates of the starting composition of the sub-surface ocean on Enceladus, we have modelled how the ocean interacts with a silicate simulant representing the rocky interior. The results from these models define a hypothesized modern ocean chemistry and provide an insight into the geochemical reactions occurring at the water-rock interface. The results from this work support observations made by Cassini, suggesting our chosen starting conditions could provide an insight into the history of Enceladus

Thermochemical modelling of the subsurface environment of Enceladus to derive potential carbon reaction pathways

The subsurface environment of Enceladus is potentially habitable: there is a global subsurface ocean [1], energy from hydrothermal activity [2] and bioessential elements [3]. Carbon, as a fundamental bioessential element, is critical for life, so understanding how it is processed within the Enceladus environment is crucial in assessing this moon’s potential habitability. Evidence from the south polar plumes suggests that carbon is likely to be bound within the silicate interior [4] and liberated through water-rock (silicate-ocean) interactions

Modelling the Rock-Water Interactions in the Sub-surface Environment of Enceladus

Understanding the geochemical cycles occuring at the rock-water interface on Enceladus is crucial in establishing the potential habitability of the sub-surface environment. The work to be presented focuses on the early ocean’s interaction with the silicate interior, with future work exploring the modern-day sub-surface environment on Enceladus. In preliminary studies we have used thermochemical modelling (CHIM-XPT) [1] to determine the chemical composition of the sub-surface ocean. The modelling focuses on the interaction of an ‘initial’ ocean chemistry with a defined silicate interior [2] to generate a modern ocean composition. We have defined the chemistry for the silicate interior based upon the chemical composition of a CI carbonaceous chondrite [3]. In the preliminary modelling we have used two different ‘initial’ compositions for the sub-surface ocean that represent different theories on its origin. The first uses a dilute sodium chloride solution, based upon the assumption that the subsurface ocean originated as almost pure water [4]. The second is based upon the assumption that the water originated from melted cometary ice [5], with a cometary composition based upon data collected from 67P [6]. We have explored the full temperature and pressure ranges anticipated at the rock-water interface. We will present the results from this preliminary modelling, the output of which will generate a modern-day ocean composition. This will be used in subsequent modelling and simulation experiments. We then plan to model the modern-day sub-surface environment to understand the full range of chemical cycles occurring at the rock-water interface. We will use the subsurface ocean composition determined by the preliminary modelling and the chemistry for the silicate interior that has already been defined. This work will have a specific focus on carbon cycling occurring within the sub-surface environment, gaining a better understanding about the potential habitability of this environment. References: [1] Reed, M. H., Spycher, N. F., Palandri, J., (2010) User guide for CHIM-XPT, University of Oregon, Oregon [2] Hamp R. E. et al., (2019), 50th LPSC 2019, Abstract 1091 [3] Zolotov, M., (2007) Geophys Res Let, L23203 [4] Brown R. H. et al, (2006) Science, 311, 1425-1428 [5] Neveu, M., et al., (2017) Geochim et Cosmochim, 212, 324-371 [6] Hertier K. H., et al., (2017) RAS monthly notices, 46

An expanded evaluation of protein function prediction methods shows an improvement in accuracy

Background: A major bottleneck in our understanding of the molecular underpinnings of life is the assignment of function to proteins. While molecular experiments provide the most reliable annotation of proteins, their relatively low throughput and restricted purview have led to an increasing role for computational function prediction. However, assessing methods for protein function prediction and tracking progress in the field remain challenging. Results: We conducted the second critical assessment of functional annotation (CAFA), a timed challenge to assess computational methods that automatically assign protein function. We evaluated 126 methods from 56 research groups for their ability to predict biological functions using Gene Ontology and gene-disease associations using Human Phenotype Ontology on a set of 3681 proteins from 18 species. CAFA2 featured expanded analysis compared with CAFA1, with regards to data set size, variety, and assessment metrics. To review progress in the field, the analysis compared the best methods from CAFA1 to those of CAFA2. Conclusions: The top-performing methods in CAFA2 outperformed those from CAFA1. This increased accuracy can be attributed to a combination of the growing number of experimental annotations and improved methods for function prediction. The assessment also revealed that the definition of top-performing algorithms is ontology specific, that different performance metrics can be used to probe the nature of accurate predictions, and the relative diversity of predictions in the biological process and human phenotype ontologies. While there was methodological improvement between CAFA1 and CAFA2, the interpretation of results and usefulness of individual methods remain context-dependent. Keywords: Protein function prediction, Disease gene prioritizationpublishedVersio