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Comment by motters | Hacker News Reader

In the search for exobiology one possible sign to look for within planetary spectra might be a predictable annual oscillation of carbon dioxide levels as occurs on Earth when plants photosynthesize more in the summer than the winter.

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There is a funny story about when Carl Sagan brought James Lovelock into the NASA exobiology think tank set up to design experiments that could determine if there was life on Mars. Lovelock, being your archetypal scientific maverick got to thinking and with his experience with CFCs and Gaia theory he deduced that all one needed was a telltale signature: a seasonal pattern of waste compounds excreted into the atmosphere. He told Sagan, they trained the appropriate detectors and started looking. Sure enough, there were quite obvious seasonal waste deposit blooms exactly where Lovelock had anticipated. Conclusion: there IS life[-like processes] on Mars. The fact that this was not "hard" evidence drove the revelation under the rug because it does not play into the hands of the scientific community as a whole which needed experiments that required us to send probes and develop technologies to get "hard" evidence. Which I don't refute is the correct method (we would need this before a categorical "life on mars" conclusion could be given the weight of the scientific community), but I think it would be a kind of vindication of Lovelock's brilliance that HIS method is more "useful" in the real search for exobiology. Mars is in a very sweet spot that allows us to confirm our suspicions and validate our methods before we go looking and finding this "life" shit all over the place (literally).

EDIT:

as other comments are pointing out I think "seasonal" is misused, but I think you get my point.

Citation? I thought the discover of methane on Mars was more recent...

I (quite deliberately) didn't say methane. And this isn't wikipedia, take it or leave it. Or, you know, contribute to the discussion.

EDIT:

sorry, didn't mean to be cranky, just sick of "citation" comments on HN. If I remember correctly it was an anecdote during a BBC documentary "Beautiful Minds" [1] which is well worth watching in full. Lovelock is one of my very favourite scientists - one of the few that write like poets (along with E.O. Wilson)

[1: http://www.youtube.com/watch?v=j6H9cYScMkE]

When it's winter in the Northern Hemisphere, it's summer in the Southern Hemisphere, and vice versa. It's just the case with the Earth than most of the land masses are on the Northern Hemisphere, but would not necessarily be the case with another planet.

Yes, but it's even more complicated. According to Wikipedia (https://en.wikipedia.org/wiki/Oxigen#Photosynthesis_and_resp... ), the green algae and cyanobacteria in the ocean produce between 70% and 45% of the free oxygen. (It's a lot of variation in the estimation.)

True, but just measuring carbon dioxide for the whole planet does show a distinct seasonal variance and that's for the reasons previously stated - there's a lot of land mass in the northern hemisphere and terrestrial plant life has a significant effect.

Possibly on exoplanets there might be similar asymmetries, or the asymmetry of an elliptical orbit. Seasonal variation in atmospheric gasses aren't necessarily a certain sign of life since there could be other non-biological causes, but they're a big clue.

Conflating two different effects. What you describe is due to the Earth's tilt. There's a smaller but globally significant effect due to moving closer/farther from the Sun in Earth's elliptical orbit.

provided the planet wobbles in its rotation and has a summer/winter cycle

I assume that the orbits of most planets is not perfectly circular and that the axis of rotation is not usually perfectly aligned with that of the host star.

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