Finally!
yesterday, NASA really stirred people up with a cryptic announcement of a press conference relating to astrobiology. Today, this NASA blog post has quieted a little of the speculation.
The conference, it turns out,. will discuss the issues relating to "shadow biospheres" with different biochemistry. And it's about damned time! I've been lamenting for ... well, decades now, really, that the search for "extra-terrestrial life" was being too narrowly confined to a definition of life that really means "Earth-type life". All the basic assumptions included the unspoken assumption that all viable biospheres must be Earthlike, and all possible biochemistries built upon the same chemical basis as our biochemistry. Many learned scientists have declaimed at length upon the pronunciation that a CHONP-based biochemistry is the only possible one, because it's what works here, and all the alternative biochemistries people have proposed won't work here.
Except of course, that in recent years we've found different biochemistries right here on Earth. Metabolic cycles based upon oxidizing sulfur, for example, that are viable only within deep-sea black smokers. What happens on a planet where the predominant environment is like that of a black smoker? And as the blog points out, this article in the International Journal of Astrobiology asks whether our planet could as easily have gone down the path of using arsenic instead of phosphorus, and points out that arsenic is toxic to us precisely because it so easily - yet not exactly - substitutes for phosphorus.
Who knows what could be a viable biochemistry in, say, a methane-hydrogen atmosphere under two hundred bar of pressure at 160K? Or perhaps an atmosphere of sulfuric acid vapor at two bar and 900K? We for sure don't know. We haven't even tried to find out.
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