Science Forums 2

[CraigD]

It’s generally accepted that the pressure at the Earth’s mantel-core boundary is about (source), which per the experiments referenced in post #57 “problem with the ‘Earth has a hydrogen core’ hypothesis” of this thread’s parent is within the range at which metallic hydrogen is known to occur at reasonable temperatures. The difficulty with they “Earth has a hydrogen core” hypothesis is not that it’s physically impossible, but the calculated density of the core is too low to account for the mass of the Earth as observed by its surface gravity, or for the presence of material of ordinary density in its mantel and crust. Although there’s little to no direct measurement of the density of metallic hydrogen at a given pressure, it’s believed to vary fairly linearly from it’s liquid density at atmospheric pressure. Thus, for hydrogen to be at the density required for the Earth’s core – around (source), the pressure would have to be being produced not just by gravity pulling the outer material toward it, but by some sort of exotic, strong container – a pressure vessel. At the pressure expected to exist at the Earth core, metallic hydrogen would be at about the density it’s believed to be in the greatest range of depths of Jupiter, near it’s mean density of .

Jupiter and other gas giant planets, it’s worth noting, are believed to consist of a layer of primarily hydrogen gas, over a layer of primarily liquid hydrogen, over a thick layer of metallic hydrogen, possibly over a small core with density and composition similar to Earth or other small, rocky planets – possibly, because while there’s scientific consensus that such a core existed during their formation, there’s uncertainty if these cores still exist, or if they have been melted and carried by convection currents into metallic hydrogen layer.

As I noted in “problem with the ‘Earth has a hydrogen core’ hypothesis”, even if it can be show to be physically possible that Earth, or any other body, has a dense metallic hydrogen core, to be accepted as a scientific hypothesis, a scientifically possible explanation of how the body got that way must be included.

Other than artificial engineering – which would be an extraordinary theory requiring extraordinary evidence – I can’t imagine the Earth having a pressure vessel contained core.

Another problem with the hypothesis is the Earth’s small mass compared to gas giants like Jupiter, which result in it having too little gravitational attraction to sweep up and retain elements with low density in a protoplanetary environment (whatever was present before the planets existed, and from which they were presumably formed). Were the Earth able to do accrete much hydrogen, it should, like Jupiter, currently have a mostly hydrogen atmosphere, so even without resorting to fundamental (and mathematically taxing) mechanical models of how bodies accrete and retain materials of different densities (Jean’s escape, etc.), we can conclude that despite the presence of ample hydrogen in the protoplanetary environment, bodies of Earth’s mass are unable to accrete and retain them. The only possible way around this problem I can imagine is to assume that the protoplanetary environment contained large, dense masses of metallic hydrogen at effectively zero pressure, which we know from theory, experiment, and observation of present-day interplanetary space not to be the plausible.

In short, intriguing and radical as the as “Earth has a hydrogen core” hypothesis is, I’ve seen no adequate explanation of these several serious problems with it, so must remain a supporter of the mainstream model of a primarily iron cored Earth.