Other
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agusm.p43a..07h&link_type=abstract
American Geophysical Union, Spring Meeting 2007, abstract #P43A-07
Other
4832 Hydrothermal Systems (0450, 1034, 3017, 3616, 8135, 8424), 5220 Hydrothermal Systems And Weathering On Other Planets, 5418 Heat Flow
Scientific paper
The ferromagnesian silicate minerals olivine and clinopyroxene are dominant in planetary mantles, and similar assemblages likely also typify the subsurface lithologies of icy moons endowed with rocky interiors, such as Jupiter's Europa. Water is also common in the Solar System. Liquid water may persist to the present day on Mars, Europa, Callisto, Enceladus and Titan. Within the P-T window applicable to ocean/seafloor interaction (10-200 MPa, 273-700 K), the presence of water causes olivine and clinopyroxene to be unstable with respect to the serpentine minerals (antigorite, lizardite and chrysotile). The ensuing hydration reaction, termed 'serpentinization', essentially acts to re-equilibrate the nascent water-deficient high-temperature state that attended planetary formation to the water-saturated low- temperature state that characterizes the planetary seafloor environment. Importantly, thermodynamic considerations require that this process is accompanied by the release of both (i) heat energy resulting from the exothermic nature of the reaction; and (ii) H2 gas resulting from unlike FeMg-1 partitioning in the reactants and products of the reaction. Because of their potential to provide heat energy, nutrients and electron- donors for extraterrestrial metabolism in the absense of sunlight, and act as crucibles for Fischer-Tropsch-type (FTT-) synthesis of hydrocarbons, serpentinization-driven hydrothermal systems are of considerable interest to astrobiology. By assuming a bulk peridotitic composition and applying new insights on cracking depth, we constrain the potential heat- and H2 flux of extraterrestrial serpentinization over time. We further examine how different kinetic considerations affect the longevity of such systems. In the absence of crustal rejuvenation and under our assumed ideal conditions, serpentinization through progressive cracking persists on planetary timescales and generates heat on a globally averaged basis at a fraction of a percent of present-day terrestrial radiogenic heating, whilst producing hydrogen at rates of 109-1010 molecules cm-2s-1. These values lie at the limiting extreme capable of sustaining life on Earth. We argue that the absence of macronutrient delivery, specifically phosphorus and electron acceptors (CO2, NO3-, etc.), may further be inhibitive of biology under these conditions. Serpentinization accompanying the initial onset of ocean/seafloor interaction, on the other hand, enjoys much shorter lifetimes on the order of 106 - 108 years, depending mostly on temperature and fluid accessibility. Although concomitant heat and hydrogen production is on the order of that encountered in hydrothermal systems on Earth today, such systems may be prohibitively short-lived to evolve and sustain biology.
Harnmeijer Jelte
Vance Stephanie
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