TAEM – Could you expand upon your atmospheric studies as they have a direct relationship to what would effect explorers on other worlds and where we should look to discover life forms.
My research background is in the area of chemistry and dynamics of planetary atmospheres. I’ve worked extensively on the chemistry of the Earth’s middle atmosphere (stratosphere, mesosphere and lower thermosphere) and its chemical and dynamical response to solar effects and climate forcing. This work entails several topics related to ozone chemistry, the budget of the greenhouse gases such as water vapor, carbon dioxide and ozone, and the formation of Earth’s highest clouds – noctilucent clouds (also called polar mesospheric clouds PMCs, at around 80-85 km altitude). I’m also interested in the long-term changes in the atmosphere due to human activities, such as lower atmosphere global warming, upper atmosphere cooling, and middle and upper atmosphere weather. I’m a co-investigator on the AIM (Aeronomy of Ice in the Mesosphere) satellite mission that is focused on the study of these high altitude clouds and how they respond to global change. The public website for this mission is at: http://aim.hamptonu.edu
I’ve also been involved in the New Horizons Pluto mission as a co-investigator: http://pluto.jhuapl.edu
An additional project is the ARES Mars Airplane: http://marsairplane.larc.nasa.gov
This was to be the first airplane to fly over another planet, but this mission is still under development as a concept. My role in that project is to provide atmospheric science input on the environment in which the airplane will fly, and to make chemical and dynamical measurements of the lower atmosphere. My other role is to search for biomarkers such as methane that might be released as a metabolic by-product of subsurface bacteria like terrestrial methanogens, which we know by laboratory experiments can live in the subsurface of Mars from laboratory simulations, and which would use atmospheric H2 and CO as metabolic energy sources. These are a form of extremophiles that live in extreme environments on Earth, and are also chemi-synthesizers. They do not need sunlight, but live off of the chemical bond energy of molecules that are present in the ambient atmosphere.
Tentative detection of methane has been reported in the atmosphere of Mars, but its presence is still controversial. Given that the chemical lifetime of methane on Mars is about 100 years, its presence there would mean some recent or continual subsurface source. On Earth methane is produced by biology, but a small portion is by geochemistry such as percolating water through volcanic magma. Since Mars is volcanically dead, the latter may be unlikely. But again, this is controversial. I mentioned in my 2002 paper that one can distinguish methane produced by biology from that produced by geochemistry by looking at the C/H isotopes in the methane. Life tends to enhance the 12C isotope relative to 13C, and that makes the isotopic partitioning also useful as biomarkers.
I published a paper in 2002 predicting methane on Mars as a potential biomarker. The presence of methane in any exoplanet’s atmosphere that also has quite a bit of oxygen in chemical forms such as O2 or CO2 might make methane a biomarker, since methane is not an equilibrium state – it rapidly oxidizes. Another way of saying this is that methane is a disequilibrium gas.
TAEM – What type of atmospheres would govern life form creativity and what possibilities we have discovered so far both within our solar system and on exoplanets elsewhere.
We have discovered water and carbon monoxide (which implies carbon dioxide) in exoplanet atmospheres, which suggest that atmospheres like we find on the terrestrial planets in our solar system like Mars and Venus may be common. It is thought that Earth’s early atmosphere was also dominated by CO2, but with plate tectonics and weather removing CO2 and an input of water from comets and asteroids, the Earth’s atmosphere evolved to the nitrogen dominated atmosphere with a dynamic hydrosphere as we have now. The development of photosynthetic life was the source of oxygen about 2.2-2.5 billion years ago, and oxygen accumulated to what we have now.
But we also find gas giant planets like those in our own solar system elsewhere. Those are dominated by hydrogen and helium, but have all sorts of variation on this basic state. However, we have found such a diverse range of types of exoplanets that the possibilities for life much different than that on Earth is plausible. Especially on exoplanets such as water worlds with water oceans thousands of km thick might harbor life like in the deep oceans on Earth but much more extreme.
TAEM – What type of biomarkers would indicate such findings in the future?
With only one example of life known, that on Earth, I think we need to use that as our guide, at least until we know more about the emergence of complexity in the universe. So on Earth life’s presence is most easily detected at remote distances by the disequilibrium gases I mentioned above. Things like methane, hydrogen sulfide, and even ozone would be useful for remote inference of terrestrial type life-forms.
Of course, all the above pertains to simple life such as bacteria. More complex life could have more complex markers of its existence. Multicellular organisms developed rapidly on Earth once they came on the scene, and we don’t know the end of that evolution. Earth is young by galactic standards, and evolution may take life to much further levels of organization than we see on Earth now.
TAEM – What importance does astrobiology play in all future explorations and what can its findings reveal for life as we know it.
I think finding life elsewhere would be one of the greatest discoveries in history, and would have a huge impact on almost every aspect of human thought. Astrobiology, which is the study of the story of life in the universe, is thus an ideal motivation for exploration and a great guide in our research.
Astrobiology findings also help us understand our own story of Earth life’s evolution and its connections, which are numerous, to the rest of the universe. In short, astrobiology pulls all the sciences together to help us understand our place in the universe.