methane ethane acetylene nitrogen HCN Photochemistry at the heart of Titan’s surface-atmosphere evolution λ < 1450 Å λ ≈ 2000 Å
Quantification of the methane consumption (simplified) Net photochemical destruction rate of CH 4 (Lavvas, et al. 2008) p-l= -3.5 x 10 -13 g cm -2 s -1 referred to the surface Mass per area of methane in atmosphere ~ P/g = 370 g cm -2 Lifetime of atmospheric methane: -P/g(p-l) = 35 million years Amount of methane that must be supplied to the surface over time Need 4.5 x 10 9 years /3.5 x 10 7 years ~ 100 x present atmospheric methane over the age of the solar system. or 100P/g = 3.7 x 10 4 g cm -2 / (0.7, 0.4 g cm -3 ) = (0.5, 0.9) km thick layer of (C 2 H 6, CH 4 ) over the age of the solar system Methane must be resupplied through time by outgassing from the interior.
Titan’s Milankovitch cycles: precession of Saturn’s eccentric orbit
Cycling of lakes/seas on Titan Seasonal 30 years Methane-rich Ethane/propane-rich Croll-Milankovitch 50,000 years Ethane/propane-rich Precipitates (C 2 H 2, HCN…) Lower viscosity waves Higher viscosity smooth “Hydration/d ehydration” cycling SeasonalCroll-Milankovitch No analog exists in Earth’s hydrologic cycle for this kind of complexity
Life in ethane-methane seas on Titan is a far more stringent test of a separate second origin than life found on Mars, Europa, or Enceladus. Impact exchange of material between bodies in our solar system implies a fundamental difficulty in proving that life “like us” had a separate origin. Life in a hydrocarbon sea is so fundamentally different-- at the molecular level— that it immediately would imply a second, separate origin of life. Titan has a big advantage over other astrobiological targets ? Titan No planetary protection issues: landing in the hydrocarbon lakes sterilizes the probe. Easy access to the lakes: no radiation, no drilling, just repeat Huygens mission....
LPL/JPL/NASA/USGS “ If life is an intrinsic property of chemical reactivity, life should exist on Titan. “Indeed, for life not to exist on Titan, we would have to argue that life is not an intrinsic property of the reactivity of carbon-containing molecules under conditions where they are stable.” Limits of Organic Life, National Research Council 2007
TiME: The Titan Mare Explorer A Discovery Mission to an Extraterrestrial Sea
We must go back to the Saturn system...if we want to test whether the origin of life is a common cosmic phenomenon