Special Plenary Sessions

The Deep History of a Carbon Atom
Primo Levi’s short story, “The Story of a Carbon Atom,” tracked the path of a carbon atom. The story begins, “Our character lies for hundreds of millions of years, bound to three atoms of oxygen and one of calcium, in the form of limestone:  it already has a very long cosmic history behind it, but we shall ignore it.” This session will tell the long cosmic history of that atom, beginning with the formation of carbon in a star, and ending with the atom involved in prebiotic chemical reactions on Earth.

Speakers from various disciplines will track this history. Karen Meech (University of Hawaii) will describe the astrophysical beginnings of a carbon atom, and how carbon atoms are delivered as part of their water reservoirs. Andrew Steele (Carnegie Institution of Washington) will discuss the geochemistry of carbon — how a planet processes it. Michael Callahan (NASA Goddard Space Flight Center) will explain how carbon in a planet participates in the prebiotic chemistry that eventually led to life on Earth. The session will be moderated by Jamie Elsila (NASA Goddard Space Flight Center).

The Origin and Subsequent Evolution of Life
Recent years have witnessed dramatic advances in our understanding of the early steps in the transition from a prebiotic world to a world transformed by a biotic component. These early steps are presumed to include the evolution of collectively autocatalytic networks of molecules, as well as the evolution of protocells that define the boundary between living and non-living matter.

Since the earliest cellular life, innovations caused by gene duplication and divergence, novel gene fusions/fission, and transfer of genes between phylogenetically distinct groups have led to an explosive diversification of the metabolic and regulatory networks within cells, enabling colonization of new environmental niches as well as new mechanisms for cooperative interactions between cells. The hierarchy of life — genes within genomes, organelles within cells, cells within organisms, and organisms within societies — is not a starting condition of the evolutionary process, but an outcome of a series of major transitions in which units of low complexity combine to form units of high complexity. Ongoing revolutions in genomics and informatics are giving new insights into the processes by which such transitions occur.

In this session, Nick Hud (Georgia Institute of Technology) and Rachel Whitaker (University of Illinois) will review advances in our understanding of the origin and subsequent evolution of life on Earth, and consider how this new knowledge is likely to influence how we search for life elsewhere in the universe.

Sustained Habitability on a Dynamic Early Earth
We know something about the habitability of early Earth, but many questions remain. Convincing evidence for life dates back to only 3.5 Ga, whereas Earth itself is a billion years older. Despite the faintness of the young Sun, conditions near Earth’s surface may have been too hot for life for hundreds of millions of years, either sporadically as a consequence of impacts, or more generally as a consequence of high atmospheric CO₂ levels. The Archean (2.5–3.8 Ga) was more clement, but the discrepancy between oxygen isotope data from cherts, which suggest high surface temperatures, and evidence for repeated glaciations has not been satisfactorily resolved. Climate may have been stabilized during this time by a combination of feedback loops involving both CO₂ and CH₄. Like now, methane was mostly biological in origin, so the climate control system could be described as being “Gaian.” The rise of atmospheric O₂ near 2.4 Ga probably triggered the glaciations that occurred at that time, although some authors have argued that this causality was reversed. The resulting Proterozoic climate was less stable and “boring” than previously thought, as glaciations have now been reported at ~1.8 Ga and ~1.2 Ga, in addition to the well-known Snowball Earth events of the Neoproterozoic. Better empirical constraints on surface temperature and on atmospheric O₂ and CO₂ are needed to reach consensus on what the early Earth environment was really like.

This session will be presented by James F. Kasting (Pennsylvania State University).

Planets in Perspective:  Where’s the Energy?
In the previous two decades, planetary exploration has observed one mantra:  “Follow the Water.” However, as the field of astrobiology has matured, particularly with respect to planetary environments and the broad range of possible ways that potentially habitable planets have formed and evolved, we may be standing on the precipice of a shift toward “Follow the Energy.” This theme recognizes that planetary processes are the likely precursors to life, and inspires new ways of assessing the habitability of a planet based not only on its ingredients, but also on a holistic assessment of its systems and cycles.

A panel moderated by Britney Schmidt (Georgia Institute of Technology) will feature experts on Mars, Europa, Enceladus, Titan, and Earth who seek to liven the debate on forming hypotheses and selecting future missions that are likely to be shaped by astrobiology.

Understanding and Recognizing Exoplanet Habitability
Habitability is a measure of an environment’s potential to support life. For exoplanets, the concept of habitability can be used broadly to inform our calculations of the possibility and distribution of life elsewhere or as a practical tool to inform mission designs prioritize specific targets in the search for extrasolar life.

Although a planet’s habitability depends critically on the effect of stellar type and planetary semi-major axis on climate balance, many additional factors have been identified that can affect a planet’s environment and its potential ability to support life. Key abiotic processes affecting the resultant planetary environment include photochemistry, stellar effects on climate balance, atmospheric loss, and gravitational interactions with the star. Understanding these processes will help us identify exoplanets that are most likely to be habitable, and will illuminate global characteristics of habitable planets that may be observable.

Astronomical observations to assess habitability may include searching for the presence of surface liquid using specular reflectance, or “glint”; determining surface temperature and pressure; and more comprehensive assays to detect the presence of greenhouse gases and assess planetary climate. In the near future, groundbased surveys and the NASA K2 and TESS missions will discover rocky exoplanets in the habitable zones of nearby stars. Larger telescopic facilities, including planned large groundbased facilities, the James Webb Space Telescope, and direct imaging missions under study such as AFTA, Exo-C, and Exo-S will allow us to study these nearby targets via multi-wavelength photometry and spectroscopy to search for signs of habitability and life.

Rory Barnes (University of Washington) and Victoria Meadows (University of Washington) will discuss recent advances in modeling the complex interplay of planetary system processes that affect habitability. They will also discuss our current understanding of the astronomical measurements needed to identify planetary habitability, and the feasibility of making these measurements with upcoming telescopic facilities.

Real Life or Fantasy:  Biosignatures or Abiosignatures in Astrobiology
One of the fundamental pursuits of astrobiology is to find life elsewhere — a pursuit often complicated by natural processes masking or mimicking signals that we would normally attribute to the presence of life. Shawn Domagal-Goldman (NASA Goddard Space Flight Center) and Nicola McLoughlin (University of Bergen) will introduce common life-detection criteria and a range of biosignatures and abiosignatures across several disciplines.

Sonny Harmon (Pennsylvania State University) will moderate a panel discussion with topics such as historical false positives, current detection criteria, and the future strategies for identifying robust indicators of life and distinguishing these from abiotic mimics. Audience participation is encouraged, so bring your best questions, comments, and concerns.

Improving Astrobiology Education Through Digital Learning Research
The astrobiology community has been incorporating digital technologies to support communication across space, time, and discipline since its inception. These technologies have been extended in more recent years to serve learners in a variety of settings, such as Massive Open Online Courses (MOOCs), virtual field trips, and eMentoring programs, to name just a few.

As more astrobiologists adopt digital-learning modalities, important questions arise regarding the role of technology, teaching quality, new pedagogies, and how to foster creativity and collaboration. These questions can best be addressed by focusing on insights and opportunities offered by analyses of existing learning sciences research, and studying how it informs instruction in digital environments.

George Siemens (University of Texas at Arlington) is an educator and researcher on learning, networks, analytics and visualization, openness, and organizational effectiveness in digital environments. He is a pioneer of the MOOC movement, directs the MOOC Research Initiative, and leads the LINK Lab at the University of Texas, Arlington, which includes investigations into the role of online learning in the university environment, the effectiveness of alternative teaching and learning models, and the influence of data and analytics on higher-education practices.

This presentation will provide an overview of what is known about digital learning and how the astrobiology community can take advantage of that research base in order to accelerate teaching and learning effectiveness.

Seeking Astrobiology Input to Mars 2020 Landing Site Selection
The proposed Mars 2020 rover mission has two objectives of high importance to astrobiology:  (1) to carry out in situ exploration operations seeking the signs of past life, and (2) to collect samples of martian material and seal them in individual tubes for possible return to Earth for detailed analysis, including assessment of potential biosignatures.

Mars has varied geological terrain. In order to maximize the chances of making a major astrobiological discovery, it is crucial to select a landing site that offers the highest chances of addressing these life-related objectives. Although the formal landing site selection process is open to all, the purpose of this session is to solicit specific input from the astrobiology community about the desired attributes of potential landing sites and the rationale for prioritizing these attributes. This session seeks to foster broader intellectual inputs from the astrobiology community. The results of this discussion will be provided to the landing site selection committee.