Well we are back from our fantastic visit to Chile and the 2019 total solar eclipse. This post has a few additional comments on that trip and mainly provide a calendar update for upcoming conferences and some summary comments on the Astrobiology for Astronomers Workshop conducted at Caltech.
First up even though the Astrobiology for Astronomers Workshop is still ongoing and if you don't get overloaded with information there, don't forget to sign up for the free Ninth International Conference on Mars, July 22-25 to be held also at Caltech. See all of you Martians there!
Next, we received an email from OCA Dave Kodama sharing a 360 x 180 degree panoramic view of the Southern Hemisphere sky that he prepared during his Chile eclipse adventure. This image shows a part of the night sky from the Observatorio Collowara outside of La Serena, Chile.
|One view of the southern night sky from Observatorio Collowara in Chile (Source: OCA Dave Kodama)|
The neat way that Dave prepared the images is that a full 360 x 180 degree panorama can be explored further on your computer where you can use your mouse to move all around on the night sky and get the full experience. I found the view entirely enjoyable and wanted to do something like that but we had little free time and were clouded out so much of the time. So check it out and enjoy your mouse driven tour around the Chilean night sky at the follow web reference at:
Next, as all of you observers know very well, we have to watch out for clouds. In my review of a modern meteorology textbook, I found this drawing and explanation of how changing wind speed over smooth surfaces and obstacles can cause the air mass to rise and form clouds. This seems like a good explanation of why we experienced so many clouds while visiting Rapa Nui (Easter Island).
|This same effect might explain why Easter Island was so cloudy (Source: Ahrens & Henson, "Meteorology Today")|
Finally, for our last odds and ends comment regarding the trip to Chile, Resident Astronomer Peggy, desiring to cut back a little bit from all of our wine sampling in Chile, found the ideal way to easily have just one glass of wine per day! Hmm, as much as I appreciate the idea, I don't think that meets the overall goal!
|Resident Astronomer Peggy discovers how to have just one glass of wine per day (Source: Palmia Observatory)|
Ok, ok, let's get on to some summary comments from the NASA sponsored 2019 Sagan Exoplanet Summary Workshop, titled Astrobiology for Astronomers, conducted at Caltech from July 14-19. I met up there with Math Whiz, Dave and we slogged though 2 days of presentations covering a lot of the technical details from biologists and geologists covering what were possible indicators of life on exoplanets that hopefully, the astronomers in the room would be able to detect. One of the pioneers in the field was of course, Carl Sagan, who was fondly remembered in the opening presentation.
|Kickoff presentation at 2019 workshop with a thanks to Carl Sagan (Source: Victoria Meadows, U of Washington)|
So, there was so much technical detail, even though it was mostly conducted so that the many astronomers in the audience would follow along, it is not easy for me to summarize more than maybe just one or two main points that made an impression on me.
A key point that we heard was that for an exoplanet to have life it is not enough just to be in the so called habitable zone, which just means near enough to the sun to have liquid water on the surface of the planet. So the planet has to be located where this can happen and also have enough mass and gravity to maintain water in the liquid state. But this alone is not sufficient and it is necessary to cover the entire evolutionary history of the planet. In the diagram below, Sean Raymond, goes over the formation of a planet for initial beginnings of accretion of dust and pebbles to the bombardment and impacts of larger planetesimals. Anywhere along this evolutionary growth curve there is room for a planet, in the habitable zone, to have lost or missed any of the necessary conditions for life.
|Formation of planets includes various accretion and planetary impacts (Source: Sean Raymond, Lab d'Astrophysique de Bardeaux)|
If we consider the impact of a large planetesimal, such as a moon forming event, then all of the existing water in its oceans on the protoplanet would have been boiled away. Check out this artist's impression of what it might have looked like. Having all of its water in the atmosphere, leads to some different astrophysical processes that affect the planet's surface and its water.
|Planetary impacts, like this imagined moon forming impact, (Source: Tim Lyons, UCR)|
So the entire surface of the planet could have been molten 4.5 billion years ago. One of the presenters, circulated a rock sample for us to examine and handle, that came from a location in Canada where the rocks have not been buried or subducted and this particular sample is found to be over 4 billion years old. Hmm, that is pretty neat, but I didn't realize that the rock would have some writing on it!
|Have you ever held a four billion old rock in your hand? (Source: Dustin Trail, U of Rochester)|
So, we have rock samples that go back to that early part of the Earth's history and simulations and calculations showing what might have been going on in the atmosphere are also very interesting. A large moon forming impact or even smaller, say Vesta or Ceres size impact, has the potential to vaporize all of the existing water near the surface. One the water is vaporized and covers the entire planet, the sun can photoionize the water and the hydrogen is subject to atmospheric escape and the oxygen mostly remains to react to with carbon and other elements. Some hydrogen combines with carbon to make methane. In the chart below, taken from Kevin Zahnle's presentation, you can see how as the planet cools, the amounts of predicted methane and carbon dioxide rise and fall as conditions on the cooling progresses.
|Development and evolution of planetary atmosphere (Source: Kevin Zahnle, NASA Ames)|
During the lunch breaks, we made our way to Caltech Chandler Cafeteria and to the Red Door for a latte. The café has lots of different options and Dave and I were also able to have some chocolate chip cookies for desert. It was also fun to look around and imagine seeing some of our favorite characters show up. No, I don't mean professors Sean Carroll or Mike Brown and others, but the likes of Sheldon and Leonard and Howard and Raj. Hmm, they did not seem to be there. Ok, ok, it is just a TV show!
This slide from Dianne Newman's presentation shows how early on in the history of the Earth there would have vast amounts of carbon dioxide and how after being subjected to UV radiation from the sun, the amount of methane increases until it too begins to fall off as the amount of oxygen in the atmosphere goes up. The early amounts of methane are sourced by both natural, abiotic sources and by various microbial life. After the first oxygen producing organisms arise, the amount of methane falls off even faster. Remember during this time that the sun was not as luminous as it is today and with that amount of greenhouse gases present, the earth would have likely been the equivalent of Venus. There is a lot of data supporting the levels of carbon dioxide in Earth's history and it is also why just the small amount of carbon dioxide in today's atmosphere can be said to be so significant in determining the future climate of the planet. So we see that the history of the Earth includes large modifications to its atmosphere by living organisms.
|Evolutionary history of CO2, CH4 and O2 on Earth (Source: Dianne Newman, Caltech)|
|Normal respiration with oxygenic photosynthesis on Earth (Source: Dianne Newman, Caltech)|
But there are other examples and possible ones of these redox reactions that do not need to include CO2 and O2. For instance we know that early bacteria found O2 a toxin. Before the Great Oxidation Event (GOE) you would miss seeing a lot of living organisms if you relied on oxygen as a biosignature.
|But the early life history on Earth did not include oxygen in the first two billion years (Source: Dianne Newman, Caltech)|
At that time, many other reductants and oxidants could have been coupled together in the cycle for life. Check out this other example where iron, in different oxidation states is used as an electron donor in one case and as an electron acceptor in the other case. This redox set of reactions allows the organism to extract the needed energy for life from essential just the rocks around it. Iron is just example that could be relied on and there are other chemistries based on sulfur that are understood and found already in organisms on Earth. Any future mission to look for life on exoplanets needs to include these other energy cycles in its search for biosignatures.
|Other redox reactions can support life, so don't just use oxygen as a biosignature (Source: Dianne Newman, Caltech)|
Ok, that is my brief summary of some of the key concepts involved in finding biosignatures of life on exoplanets. We only know of the kind of life existing here on Earth, but we can see that the chemistry of redox reactions is wide enough that when the Gibbs free energy from the sun or geothermal or geochemical sources is included, then alternate life forms could exist and our search for exoplanet biosignatures must be wide enough to recognize this fact.
Ok, after 2 days of being at Caltech in Pasadena and listening to all of these discussions and presentations, I am completely worn out. I elected to return to the observatory, after spending one night at my favorite, or at least haunt of hotels along Colorado Boulevard, and attend the remaining sessions of the workshop through the livestreaming option. After driving the 70 odd miles from Pasadena, first of all along the dreaded and stop and go traffic of the 210 Freeway, I was glad to arrive at the observatory, where it is always 5:00 somewhere and I could replenish my alcohol level. I am also sporting one of the $5000 peso necklaces that I picked up in Rapa Nui. The life of a physicist wannabe is not that easy, but it is not that hard either!
|Finally, back from Pasadena and the dreaded 210 Freeway for a well earned martini (Source: Palmia Observatory)|
If you want to follow along with the remaining sessions of the workshop, just go to the website and click on the livestreaming option. That is certainly what Math Whiz Dave and I are going to do. Going up the dreaded 210 Freeway to attend the workshop in person is hard to justify when we can just sit back in our easy chairs and livestream the event.
Until next time,
Resident Astronomer George