Exotic Biochemistries

Check out Paul Gilster’s discussion of azotosome-based life in the methane lakes of Titan

[Ref: “Membrane alternatives in worlds without oxygen: Creation of an azotosome” Science Advances Vol. 1, No. 1 (27 February 2015), e1400067.]

His essay prompted this quick discussion.

In 1961 Isaac Asimov, who was a research Chemist as well as uber-writing machine, wrote a highly influential essay (for “Fantasy & Science-Fiction” magazine) on exotic biochemistries. For those who want to read what the Good Doctor had to say it was reprinted in the old “Cosmic Search” newsletter and is available online here:

Not as We Know it – The Chemistry of Life

Asimov suggested the following options, in order of decreasing temperature:

There, then, is my list of life chemistries, spanning the temperature range from near red heat down to near absolute zero:

1. fluorosilicone in fluorosilicone
2. fluorocarbon in sulfur
3.*nucleic acid/protein (O) in water
4. nucleic acid/protein (N) in ammonia
5. lipid in methane
6. lipid in hydrogen

Of this half dozen, the third only is life-as-we-know-it. Lest you miss it, I’ve marked it with an asterisk.

I originally read about Asimov’s typology in “Man and the Stars”, the collection of discussions on Extraterrestrial contact by the ASTRA group in Scotland published by Duncan Lunan.

A more recent discussion of exotic biochemistry, which inspired Stephen Baxter’s recent depiction of Titanian life in his novel “Ultima”, is found in William Bains’ essay here:

Many Chemistries Could Be Used
to Build Living Systems

[Ref: ASTROBIOLOGY Volume 4, Number 2, 2004 ]

In turn Bains’ work led to a collaboration with Sara Seager which provocatively argues for a hydrogen-based photosynthetic life:

Photosynthesis in Hydrogen-Dominated Atmospheres [Open Accesss]

[Ref: Life 2014, 4(4), 716-744; doi:10.3390/life4040716]

…the full implications of which are yet to be explored – the essay was published late last year. One irritating conclusion is that such H2 based biospheres might be very hard to detect remotely.

Another exotic option is the possibility of chlorinic photosynthesis, making chlorine based compounds instead of oxygen as a by-product:

The potential feasibility of chlorinic photosynthesis on exoplanets

[Ref: Astrobiology. 2010 Nov;10(9):953-63. doi: 10.1089/ast.2009.0364]

…though chlorine compounds do tend to be very opaque and may make the surface too dark to sustain life. In his “Manifold” trilogy, book 2 “Space”, Stephen Baxter imagined a world poisoned by the deliberate seeding of its oceans with chlorine producing organisms. If such a photosynthetic pathway is possible, then its spontaneous evolution in our own oceans is a possibility that we might’ve be lucky enough to avoid thus far. Other worlds, maybe not.