20 December 2017
No, not so simple. This is ANU and there are good minds with plenty of knowledge and thought, so the questions were more defined: "Is the Earth special" was the title of the session and it was translated into two subsessions, each of three experts, on "Is our planet special" and "Is life on Earth special". And this melange of differing specialisations was moderated by a fairly immoderate and amusing local researcher, Charley Lineweaver. (As a side issue, it seems Charley appears fortnightly on ABC radio, but I've never heard him: I assume he's on local radio ABC666). This was a family event, so questions invited from U15s early on, and they asked some decent questions, but otherwise, it developed into an adult event.
The first part was Jessie Christiansen of NASA, an ANU graduate who watched films in this very theatre (ANU Film Group in HC Coombs Theatre). She outlined the frequency of planets found by the Kepler mission, a NASA satellite that uses transit techniques to find planets. Suffice to say they've found tons of them, of different sizes and in different system configurations. (Very different from when my Canberra Astronomy Society team at Stromlo found extra-solar planet no.9). There are limitations on what can be observed, and our Earth would not be found from afar with current technology, but there are lots. Second up was Daniel Fabrycky of Univ of Chicago who spoke of planetary systems, basically identifying how gas giants (they make up ~10% of what we've found) can interfere with standard orbits of rocky planets and even send them off into the galaxy. Daniel presented a glorious Kepler Orrery that displays the natures of known extra-solar systems to date in vigourous colour and movement (see YouTube). Third up was David J Stevenson of CIT (California Inst of Tech), a planetary scientist who threw a curveball arguing that "habitable zone" is a limited concept, essentially a function of our experience, and that all manner of planetary issues (for Earth, he identified water, plate tectonics, magnetic field and large moon) can be of relevance. Basically, given we only have one example of a planet with life, we can't foresee the possibilities.
Then the biologists. Simonetta Gribaldo of the Institut Pasteur fascinatingly outlined the evolution of life, the three main streams of Eukaryotes and Prokaryotes (comprising archaea and bacteria), their earliest known ancestor, Luca (Last Universal Common Ancestor), their likely prior evolution, their differences in cell structure (basically, they all have ribosomes in cells, but eukaryotes have cellular nuclei and prokaryotes don't). Fascinating! Also something on timelines, the oldest traces of life (~-3.5by), the Great Oxygenation Event (~-2.4by), the arrival of Eukaryotes (~-1.6by), etc. Then Jochen Brocks of ANU with an argument about the rise of algae in more energy-rich environments (~-645my) and the arrival of the Eukaryotes (bigger and requiring more energy). Then a final speaker, philosopher Kim Sterelny of ANU outlining Universal Darwinism: the requirements underlying successful Darwinian evolution.
So, is our planet or life here special, as Charley Lineweaver kept asking of the experts? Basically, they hedged their bets, essential given we really don't know and we have very limited comparisons (nil). But there are tons of planets out there around tons of stars in the Milky Way; there are all manner of conceivable biological developments that may create life and develop it with the right evolutionary conditions. The numbers are big but so far our knowledge, especially in the biological area, is small. But we can muse on it, moderately intelligently, and they did. An interesting session that introduced me to many new ideas (not least, Luca) and well entertained us. Let's just keep our eyes and ears open.
Charley Lineweaver (ANU) chaired a session on the likelihood of extraterrestrial life at ANU. Speakers were Jessie Christiansen (NASA), David J Stevenson (California IT), Daniel Fabrycky (U Chicago), Simonetta Gribaldo (Institut Pasteur), Jochen Brocks (ANU) and Kim Sterelny (ANU).