Searching for extraterrestrial life: it’s complicated


Last month I spent four intensive days at the 2015 Astrobiology Science Conference in Chicago. Among many messages I took home from this meeting is that searching for evidence of extraterrestrial life is complicated. As in difficult, challenging, frustrating, time-consuming….

Nonetheless, the growing community of scientists engaged in this endeavor are becoming more and more convinced that, ultimately, the search will be successful. As to how long it will take to find incontrovertible evidence that life exists somewhere other than Earth, few astrobiologists are willing to venture a guess – such a prediction would be, indeed, nothing more.

I’ve been going to AbSciCons for more than 10 years. The first AbSciCon I attended had no concurrent sessions. I could listen to every single talk on the agenda. This year, AbSciCon featured no less than five concurrent sessions each day plus multiple plenaries, two massive poster sessions (150 posters per), lunchtime meetings, and other special events.

The theme of this year’s conference, which drew 750 registrants, was “habitability, habitable worlds, and life.” A press conference held during the conference featured astrobiologists who are engaged in cutting-edge research into the habitability of extrasolar planets, icy planetary bodies, and planetary subsurfaces.

I can’t offer a summary of the conference, as at any given time I was missing four out of five concurrent sessions. What I can offer is a list of interesting questions and statements I heard there that provide a taste of what astrobiology is about today (I note sources where I remember them):

  • Big Questions:
    • How can we distinguish between biosignatures and abiosignatures?
    • What is “habitable”? What is a “habitable zone”? How do we define the habitable zone of a planetary system?
    • What was the relative abundance of carbon from exogenous and accreted materials on the early Earth?
    • “What does a planet do to let life get there? What exactly is the problem that life solves?” (Everett Shock, Arizona State University)
  • Origin and evolution of life:
    • When did life cross “the Darwinian threshold” from communal to individual evolution?
    • It seems more sensible to think about life beginning inside a planetary body, eventually working its way to the surface and adapting to the use of light. (Everett Shock, Arizona State University).
    • Research shows that atmospheric oxygen on Earth was low prior to the Great Oxidation Event 2.45 billion years ago. Research also shows that local and global “whiffs” of oxygen appeared in the atmosphere before that event, 3 billion years ago. If oxygen was being produced on Earth 3 billion years ago, then why did the Great Oxidation Event not occur until 2.45 billion years ago? (Jim Kasting, Penn State)
  • Carbon and life:
    • How does terrestrial carbon processing inform us about extraterrestrial habitable worlds?
    • Carbon is the backbone of life. But it might be impossible to explain how carbon in a planet participates in the prebiotic chemistry that eventually led to life on Earth. (Michael Callahan, NASA Goddard Space Flight Center).
    • Carbon itself doesn’t lead to life. It’s the interaction of carbon with its environment that leads to life. (Andrew Steele, Carnegie Institution for Science)
  • Exoplanet habitability:
    • At AbSciCon 2012, no global climate models for extrasolar planets were presented. At AbSciCon 2015, six models were presented. These models “are proving to be a very useful tool” in studying exoplanet habitability. (Rory Barnes, U. Washington).
    • A tidally locked planet, close to its star with one side always facing it, is not necessarily inhabitable. (Ibid.)
    • The early evolution of M dwarf stars may desiccate planets in their habitable zones. (Ibid.)
    • Astrobiology needs more geophysicists. We need to know what goes on inside planets as they evolve. (Ibid.)
    • The mass of a star can be just as important to planetary habitability as its luminosity is. (Ibid.)
    • “Planetary habitability is complicated.” (Ibid.)
    • Direct imaging of an exoplanet requires angular separation of star and planet and suppression of the star’s light. “We don’t have it yet for terrestrial planets.” (Vikki Meadows, U. Washington)
    • Transit transmission is a technique for looking through an exoplanet’s atmosphere (but not for observing its surface). The James Webb Space Telescope will provide the first opportunities for transit transmission observations of exoplanets. (Ibid.)
    • What global climate models are most useful to the study of exoplanet habitability?
    • Small, common stars with planets usually have multiple planets – so should the search for habitable exoplanets focus on these multiple-planet systems? (Aowama Shields, UCLA)
    • It is not logical to assume that Earthlike planets are most likely to be habitable. (Rene Heller, McMaster University)
  • Life detection:
    • Heat + pressure + time can create abiotic organic materials that are similiar in physical appearance, elemental composition, and molecular characteristics to biotic materials. So when we’re looking for fossil evidence of life – on Earth or elsewhere – we have to be really careful to distinguish between the two. (Abigail Allwood, Jet Propulsion Laboratory)
    • “The biggest lesson I’ve learned” is that “context is key” to identifying true biosignatures in the terrestrial rock record. If a potential biosignature were to be identified in a returned Mars sample, interpreting that evidence properly would require a lot of contextual evidence. (Ibid.)
    • “Habitability is the potential but not the proof for life.” (Murthy Gudipati, Jet Propulsion Laboratory)
    • We know that (on Earth) microbes can live in ice. We know little about how microbes affect ice structure. We know that ice is abundant in the solar system. (Britney Schmidt, Georgia Tech)
    • “We’re biased by what we know about life on Earth…. How much fun it is” to put aside those biases and think about other possibilities for life. (Jen Eigenbrode, NASA Goddard Space Flight Center)
    • “I leave this meeting thinking that all of Mars is habitable.” (Ibid.)



3 Responses to “Searching for extraterrestrial life: it’s complicated”

  1. SETI: still not making sense | doctorlinda Says:

    […] talks I heard at AbSciCon convinced me that the rationale for search for evidence of microbial life in our solar system is […]

  2. Exoplanets everywhere, but not another Earth | doctorlinda Says:

    […] habitability is complicated,” according to exoplanet scientist Rory Barnes. See my blog post of July 1 for some thoughts from the experts on looking for signs of life on other […]

  3. Earth-like, Earth-sized, Earth-mass: habitable? | doctorlinda Says:

    […] Habitability is complicated. As I noted in my blog post of July 1, 2015, among the many Big Questions yet to be answered by space science are: What is […]

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