THE HEAT-PIPE PLANETS HYPOTHESIS

Early terrestrial planetary development is not well understood. For Early Earth, we ask when, how, and why plate tectonics initiated, and what tectonics operated between the magma ocean phase and the onset of plate tectonics. Other terrestrial bodies in our solar system – Mercury, Venus, the Moon, Mars, and Io – have single-plate lithospheres, but it is unclear whether each lid was created via a relatively unique process, or if a similar and systematic development might have led to these lids. The “heat-pipe” tectonics of Io may resolve these questions. As the hottest terrestrial body in the solar system, Io loses heat via volcanic advection through its single-plate lithosphere. This produces a thick, cold, volcanic lithosphere, which contracts as the lithosphere continually subsides to fill the depths from which the melts were evacuated. For early Earth, this concept leads to four key predictions: thick volcanic stacks, a cold geothermal gradient, contraction, and a rapid decrease in volcanism with the onset of plate tectonics. These predictions match records from the first third of Earth’s history. For the other terrestrial planets, the predictions are the same, except that as there is no transition to plate tectonics, the fourth prediction is: preservation of a thick, strong heat-pipe lithosphere. The predictions appear met. Terrestrial planetary surfaces are dominated by volcanic rocks (the Moon is debated). Early geothermal gradients are hard to determine. Early contraction occurred. Excepting Venus, these bodies show ancient topography, out of hydrostatic equilibrium, supported by lithospheric stresses. This is hard to explain with traditional stagnant lid models, but readily accomplished via early development and fossil preservation of a heat-pipe lithosphere. Heat-pipe cooling may therefore represent a standard model for the early lithospheric development of terrestrial bodies, including large exoplanets. ... An Yin taught the presenting author how to reconstruct geologies by guiding his PhD work on the NW Indian Himalaya. An persistently advocated that we should be able to work on new geologies at will: to “drop out of a helicopter” and make contributions immediately, simply, from new observations and concomitant new hypotheses. The reconstruction skills learned from An, combined with attempts to emulate his fearlessness, helped lead to this work.