Frank Trixler offered to send me a couple of blog entries from a conference he planned to attend, and I welcomed the opportunity to present a report from the forefront of scientific research. I hope to see more scientists offering to share their impressions from professional meetings! Trixler leads a research group at Technische Universität and Ludwig-Maximilians-Universität Müal surfaces. He also runs a science outreach lab at Deutsches Museum. Many thanks to him for volunteering his time. --ESL
The Origins 2011 conference, which took place last week in Montpellier, France, was dedicated to the origins of life and its occurrence in the universe. At this meeting, scientists from very different disciplines, such as planetology, astronomy, geology, chemistry, and biology, came together to share their ideas. Participants were forced to broaden their perspectives as they had to juggle different arguments from totally different disciplines.
Here is an example: a physicist in the audience commented on the presentation of a speaker giving a talk about the habitability of planets around M-stars. He stated that the photon energy of a M-star was simply not sufficient to split water molecules, which is necessary for oxygenic photosynthesis. The speaker replied that life will manage to do so, but the physicists refused to accept this possibility, due to the lack of energy. However, the speaker made a good argument: even the photons from our Sun that reach the surface of Earth do not have sufficient energy to do this, and he suggested (probably having in mind the fact that life uses catalysis): "Ask the plant, it can do it!"
As science is based on good questions, I want to start with a bunch of them. The best way to do this is to summarize Monday's panel discussion, which addressed the International Year of Chemistry. Its topic: Perspectives on the Origin of Life. (Chair: Antonio Lazcano. Panelist speakers: Ada Yonath, Gerald Joyce and David Deamer).
Antonio Lazcano had initially planned that each of the panelist speakers would provide a 10-minute explanation of his or her view regarding the research on the origin of life and that the panel would then discuss it. Ada Yonath, however, felt somewhat uncomfortable with this prospect and suggested instead that there be a fully open dialogue with the audience, without the monologues. All of the panelists agreed and this turned out to be a very good decision, as many very inspiring questions arose:
Was there a pure RNA world or a RNA/protein mixed world? Gerald Joyce stated that it is not clear that there was ever a RNA world. But if there was, the important question arises: could there still be a classical RNA world today on earth? If so, it is not communicating with today's life. Joyce's recommendation: drill down to locations which are not in contact with our present biosphere!
Another question referred to the proton gradients which all forms of life use to produce energy. David Deamer stated that phospholipid membranes (which are necessary to generate these gradients) are very highly evolved. A very big question thus arises: How was the initial proton gradient made? Antonio Lazcano added that even today, we still don't have a theory as to how ATP biosynthesis could have started.
How did the coupling of energy with information start? Deamer stated that this is one of the biggest questions concerning origin of life research.
Can there be something below RNA? (that is, a pre-RNA world). According to Joyce: maybe! And in his own opinion: definitely!! He added that the following is a big question for young scientists: do you see any evidence that something simpler than RNA existed? It may not be like RNA at all, maybe mineral surfaces?
Later in the discussion, Gerald Joyce stated that, just as the Earth turned out not to be the center of the solar system and Humans not to be the centre of the Universe, our biology may not be the "centre" of life. For example, there is nothing special about ribozymes except they are used in us. Maybe synthetic biology could also generate others?
As we found out during the question-and-answer session, everyone had his or her own favourite environment, energy source, etc. in their origin-of-life theories. However, David Deamer suggested that it is incredibly valuable to have so many alternative hypotheses in this young field.
Complex experiments for testing hypotheses are also a task for future space exploration. Alvaro Giménez, ESA Director of Science and Robotic Exploration, spoke about ESA's future exploration plans during another panel discussion. He pointed out that ESA is striving for a stable, long-term funding line for European Mars Exploration. Of course, this raised an immediate question from the audience as to how the funding of such a program would be achieved, keeping in mind the economic problems of some states in Europe. In response, Giménez emphasized that ESA aims to be a robust and credible partner with its own technology development programme and that it will maintain a stable level of funding after ExoMars for new missions such as MSR Orbiter, a precision lander with a sample fetching rover, a Mars Network science mission and a sample return from a moon of Mars. Two candidates will be selected in 2012. Another question from the audience concerned the funding with regard to the Ganymede mission. Giménez explained that the Ganymede Mission would be financially decoupled from the Mars program. However, the final decision about Ganymede will be made in February 2012, after the US urged ESA to rethink the program and to consider the possibility of Europe carrying it out alone.
Attending the conference is almost a 12-hour working day, packed to the brim with information from many talks and even more posters. It's a very challenging and extremely subjective job to select only a few contributions for a blog. I found the following two contributions most fascinating, due to their great potential to explain many different observations with one or just a few basic principles. Finally, my review of the general parameters of habitability addresses the opposite direction, showing how extremely different worlds could exist in comparison to our own world, based on reasonable scientific assumptions and observations.
Addy Pross proposed in his talk a conceptual bridge between chemistry and biology which he terms "Dynamic Kinetic Stability" (DKS). DKS describes key concepts of Darwin's theory as particular applications of a broader chemical concept: the transition from inanimate matter in a chemical phase of evolution towards simple life, and the transition of simple life in the biological phase (described by Darwin's theory of evolution) towards complex life. He states that both are in fact just one process. The increase in complexity is always induced by a drive towards more DKS. So what does that mean? The central aspect of his theory is stability. He distinguished between thermodynamic stability of regular chemical systems and kinetic stability of replicating systems. Chemical systems are stable if they do not react. In contrast, complex, unstable organic matter can also reach a high degree of stability if they manage to replicate, and to replicate at a rate which is equal or higher than their decay rate. In this case, such systems have a high kinetic stability. As a consequence, death is just a reversion to the thermodynamic world. After his talk, someone asked if the increase in complexity is a deterministic process. Addy Pross answered that the role of complexity concerns the manner in which it assists replication. Another question was: Is DKS very environmentally dependent? Pross replied: bacteria replicate well, but put some chemicals inside the tube, and they die. So the answer: yes!
Back to planetology: Allesandro Morbidelli presented a very coherent scenario which explains the low mass of Mars, the existence and different composition of the asteroids in the belt, the mass and orbit of Earth and the high amount of water on Earth. One of the basic assumptions of the model is that the inner disc of planetesimals is truncated at 1 AU [Earth's orbital distance from the Sun] instead of extending up to 5 AU. Simulations with a disc truncated at 1 AU successfully explain the low mass of Mars. But on what is that assumption based? Giant planets formed first, and gravitational interactions with the gas disc caused them to migrate. An inward migration of Jupiter and a slightly faster inward migration of Saturn began, but stopped when Jupiter and Saturn were in their mutual 2:3 mean motion resonance, leading to a reversal of the direction of their migration. Assuming that Jupiter stopped his inward migration at 1.5 AU leads to an inner disc of planetesimals truncated at 1 AU, which causes the observed low mass of Mars. The migration of Jupiter through the asteroid belt zone removed all bodies, but the zone has been slightly repopulated with inner-belt and outer-belt bodies which explains the different composition of today's asteroid belt. The objects which moved from the outer regions towards the inner solar system delivered the water towards the end of the formation of Earth. At a later time, a reorganisation of the structure of the solar system occurred after the gas disc disappeared, which lead to the Late Heavy Bombardement according to the Nice Model.
The subtle dependence of the result on various parameters which can span a broad range of variability raises some important implications for the habitability of Earth: if Jupiter had reversed later and thus migrated closer to the Sun, then Earth would have ended up as small as Mars; if Jupiter had not migrated outwards again, then Earth would not have received its large amount of water from outer-belt bodies. In all these cases, Earth would most probably not have become a habitable world. This is highlighted by Morbidelli's title: "dangerous life of a habitable planet."
The talk given by Victoria Meadows concerning exoplanets and habitability had a very general focus: the set of parameters for habitability of exoplanets. She showed a stunning slide summarizing all the known parameters and their interactions to each other which influence the habitability of a planet. The slide was packed with boxes, including certain parameters and arrows to visualize their interdependences. This provided a very figurative impression of the tremendous complexity: there is no such thing as THE habitable zone, simply determined by the stellar radiation and the distance from the star (that's just the insolation habitable zone) - the problem is extremely multidimensional. For example, you have to consider the impact of tidal forces (presentation by Rene Heller), magnetic fields (talk by Mercedes Lopez-Morales) and stellar flares (Antigona Segura), especially for planets around M-dwarfs. And you have to consider the interplay of these parameters which can even generate counter-intuitive results. A nice example is a comment made by a participant after the talk by Lopez-Morales. The participant pointed out that the high ultraviolet flux of nearby M-stars can ionize the upper atmosphere of a nearby planet and possibly induce a shielding magnetic field. By the way: M-stars have been the subject of many talks. These cool stars are a hot topic: most stars are M-stars, and the detection of smaller exoplanets around them is much easier. Meadows refers to them as the "slum area" of habitability, as they are numerous, with low energy flux, and are exposed to harsh conditions.