Habitability of Titan

Indeed, although Titan's surface is too cold and the energy available in its environments is not abundant enough to provide conditions of habitability, the subsurface ocean may be suitable for life. As suggested by Fortes24 the possible mean temperature ofthe ocean (260 K and even 300°K in the vicinity of cryovolcanic hotspots), is not an obstacle to the development of living systems. The same is true for the pressure and pH parameters. At a depth of 200 km, the expected pressure in Titan's ocean is about 500 MPa (5 kbar), not incompatible with life as shown by terrestrial examples. The pH (aqueous solution with up to —15% by weight of NH3) would be —11.5: on Earth, bacteria can grow at pH 12. Even the limited energy resources do not exclude the sustaining of life.

Fortes has estimated that an energy flux ofabout 5 x 108 W may be available in Titan's ocean for bioactivities. In the terrestrial biosphere this value corresponds to the production of about 4 x 1011 mol of ATP per year and about 2 x 1013 g of biomass per year. Assuming an average turnover for the living systems of the order of a year, the biomass density would be 1 g/m2, which is almost in the range of

Figure 3.13, right. As seen by the Cassini camera, large plumes are ejecting fine particles in the south polar region of Enceladus (left image), like gigantic terrestrial geysers. In the same region, the CIRS instrument detected warmer area (89-91 K, compared to the surrounding temperature of 74-81 K) and correlated to the "tiger-stripes" looking fractures (right image). Credit: Left: NASA/ JPL/Space Science Institute; Right: NASA/ JPL/GSFC/Space Science Institute.

Figure 3.12, left. Model of the chemical composition of Titan's aerosols, derived from the Huygens ACP data. Credit:—F. Raulin, in G. Horneck and P. Rettberg Eds Complete Course in Astrobiology, page 232, 2007. Copyright Wiley-VCH Verlag GmbH and Co. KGaA. Reproduced with permission.

Figure 3.13, right. As seen by the Cassini camera, large plumes are ejecting fine particles in the south polar region of Enceladus (left image), like gigantic terrestrial geysers. In the same region, the CIRS instrument detected warmer area (89-91 K, compared to the surrounding temperature of 74-81 K) and correlated to the "tiger-stripes" looking fractures (right image). Credit: Left: NASA/ JPL/Space Science Institute; Right: NASA/ JPL/GSFC/Space Science Institute.

Figure 3.14, left. A model of Enceladus plumes formation, implying the presence of subsurface reservoirs of pressurized liquid water, in contact with hot rocky materials. Credit: NASA/JPL/ Space Science Institute.

Enceladus "Cold geyser" Model

HjO vapor plus Ice particles

Figure 3.14, left. A model of Enceladus plumes formation, implying the presence of subsurface reservoirs of pressurized liquid water, in contact with hot rocky materials. Credit: NASA/JPL/ Space Science Institute.

Tidal Healing

Tidal Healing

Europa's ocean. Cassini-Huygens data do not evidence any sign of biological activity on Titan's surface. In particular, the measurement of the carbon isotopic ratio in methane strongly suggests a non bio -logical origin. However, these data do not exclude the possibility of the presence of a limited biota in the sub-surface ocean of Titan.

0 0

Post a comment