The possibility of alien life in exotic forms on other worlds

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The Possibility of Alien Life in Exotic Forms on Other Worlds

Dirk Schulze-Makuch1 and Louis Irwin2

1 Department of Geology, Washington State University 2 Department of Biological Sciences, Univ. of Texas at El Paso

Titan: Some (may) like it cold

Venus: Some (may) like it hot

Composition of atmosphere: N2 ~ 90 %, CH4 ~ 5 %, Ar ~ 3 % plus minor constituents such as H2, C2H6, CO, C2H2, HCN etc

H2O vapor ~ 8 ppb, CO2 ~ 10 ppb

Photochemical haze

Organic compounds including acetylene and radicals produced by photochemical reactions


Acetylene sinking to the surface and accumulating

Methane cloud

Methane rain

Environmental Conditions on


Hydrocarbon lake or river (dominantly ethane)

Water ice, ammonia ice, silicate rocks, liquid hydrocarbons in pore spaces T ~ 180 K

Convection cells

Ammonia-Water Ocean

Rising CH4 and other

Warm Gases

Accumulating Acetylene

C2H2 + 3H2

Overheated Volatile Compounds


Life may have originated on Titan during its warmer early history and then adapted to cope with the increasingly cold conditions

But, does the Cassini-Huygens Mission support the notion of

possible life on Titan?

Mission Results in Favor of Possible Life

(1) Titan s smooth surface endogenic activity (2) Liquid ethane and methane on the surface (3) Flow channels temporary surface liquid (+ near surface reservoirs?)

(dark and bright ethane/methane and ammonia-water?)

And we know about the presence of many organic compounds .

Mission Results Against Possible Life

Absence of any large standing surface liquids

(e.g. latest discovery of dunes by Lorenz et al.,2006)

Carbon isotope fractionation rate as from Huygens GC/MS

However, the carbon isotope fractionation rate is far from conclusive

The Argument Against Possible Life

(e.g. Niemann et al., 2005)

12C/13C Titan by Huygens GC/MS:

82.3 +/- 1

Solar 12C/13C ratio (Anders and Grevesse, 1989)


Inorganic Earth Rocks (Eichmann et al., 1997: -3.6 to -9 %o) ~ 90.4

Biological Fractionation consistent with methanotrophic

affiliation of Archaea on Earth) ( ~ -37 %o)

~ 93.4

Typical bacterial methanogenesis ( = -60 to - 90%o)

> 95

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