Event Name: Habitability and Biosignatures of High-Obliquity and High-Eccentricity Exoplanets with Dr. Stephanie L. Olson
Event Time and Place: Wednesday, September 20, 2023 from 4:05 pm to 5:00pm
The habitability of any exoplanet is heavily influenced by the planet’s Obliquity and Eccentricity. Obliquity is the tilt of a planet with respect to its plane. While eccentricity is the deviation from a circular orbit for a planet. Other factors include an exoplanet’s detectable biosphere which will have photosynthesis and less so chemosynthesis. In regards to obliquity, this is what will impact the seasons and control vegetation. Having a higher obliquity will mean more dramatic seasons. Though having a modestly high obliquity will maximize vegetation. On the other hand with eccentricity unlike obliquity, total energy received changes and winter is longer. Eccentricity is what creates global seasons as a planet moves closer/further away from the sun. Eccentricity can also increase vegetation cover in regards to both space and time. So our best chances for life detection would come from a planet that has both high obliquity and high eccentricity. Also a planet with these characteristics could be great for biosignatures, including atmospheric and surface signals with regards to a planet’s ocean. A large photosynthetic biosphere is a benefit for habitability.
I found the main points convincing for the most part, in regards to her main points of eccentricity and obliquity I think Dr.Olson was very convincing. Dr.Olsen before diving into these two main points proceeded to give us the definitions of these two main points which I felt were crucial to helping her convey her points to us, as well as establishing some credibility. With obliquity being defined as the general tilt of a planet with respect to its plane. While eccentricity being defined as the deviation from a circular orbit. Next throughout her presentation everything regarding the habitability of an exo-planet was cross-referenced with the conditions of Earth. A specific example would be her mentioning earth’s obliquity which is 23.5 degrees. Then proceeding to present the audience with detailed graphs of what different obliquities for a planet would look like and coming to the conclusion that a planet with moderately high obliquity is a good quality in terms of determining the habitability of a planet. As well as adding on that obliquity impacts seasons which then impacts vegetation. Also that higher obliquity means more dramatic seasons. With eccentricity, Dr.Olson added that eccentricity is what produces the global seasons as a planet moves closer/further away from a star. Now in terms of habitability as she described it, eccentricity can also increase vegetation cover in both space & time. From a logical standpoint I agree with her on these statements. However as she began moving on from obliquity & eccentricity to warming cycles and habitability I feel she had a fallacy present. She began talking about the warming cycles of the ocean and presented graphs of our current world, where the location of the continents represented the warming cycle being influenced by the current location of the continents. However she didn’t really account for the location of land influencing the warming cycle of the planet. If the continents were to move then the relationship between land and ocean at certain latitudes would change the warming cycle. At one point of time all the continents were connected and so the warming cycle would dramatically change since then for our planet. The warming cycle of a planet is a key factor for determining the habitability levels of an exoplanet. The last major point Dr.Olsen went over was photosynthesis and its role in habitability and for this I think she did a great job of looking into its role in regards to habitability. She was quick to differentiate photosynthesis and chemosynthesis and then also did a great job relating photosynthesis to obliquity. Stating that with higher obliquity meaning marine productivity increases and higher productivity would suggest a greater spatiotemporal overlap between photons and nutrients at a high obliquity. She followed this up nicely by then relaying some more graphs. Finally to wrap up her presentation, Dr.Olsen mentioned that seasonal cycles may be required for the origin of life and with the seasons being linked to obliquity and eccentricity. This point I thought was valid and so overall I’d say most of her main points were valid and convincing. I just feel she overlooked the position of land masses and how they affect warming cycles on a planet, but other than that she was great.