Melting ice under pressure

The deep interior of Neptune, Uranus and Earth may contain some solid ice. Through first-principle molecular dynamics simulations, Lawrence Livermore National Laboratory scientists, together with University of California, Davis collaborators, used a two-phase approach to determine the melting temperature of ice VII (a high-pressure phase of ice) in pressures ranging from 100,000 to 500,000 atmospheres. For pressures between 100,000 and 400,000 atmospheres, the team, led by Eric Schwegler, found that ice melts as a molecular solid (similar to how ice melts in a cold drink). But in pressures above 450,000 atmospheres, there is a sharp increase in the slope of the melting curve due to molecular disassociation and proton diffusion in the solid, prior to melting, which is typically referred to as a superionic solid phase... It has been proposed that the cold subduction zones in Earth are likely to intersect with the high-pressure melting curve of water, which would have profound implications for the composition and transport of materials in the interior as well as the long-term evolution of the planet as it cools. The new research pinpoints the melting curve at extremely high pressures (350,000 to 450,000 atmospheres of pressure), similar to those found in the interiors Neptune, Uranus and Earth. At higher pressures, the team found that the onset of molecular dissociation and proton diffusion under pressure occurs gradually and bears many similarities to a type-II superionic solid, such as lead fluoride.

Scientific maverick’s theory on Earth’s core up for a test
SF Chronicle | Monday, November 29, 2004 | Keay Davidson
Posted on 12/05/2004 11:17:28 AM PST by SunkenCiv
http://www.freerepublic.com/focus/chat/1294934/posts

New data challenge Earth atmosphere theory
Newsdaily | September 19, 2007 | United Press International
Posted on 11/03/2007 10:30:34 AM PDT by SunkenCiv
http://www.freerepublic.com/focus/f-chat/1920521/posts

Jupiter and Saturn full of liquid metal helium
UC Berkeley | Aug 6, 2008 | Rachel Tompa
Posted on 08/06/2008 3:51:07 PM PDT by decimon
http://www.freerepublic.com/focus/chat/2057677/posts

The Centers of Planets
by Sandro Scandolo
and Raymond Jeanloz
Back in 1935, Eugene Wigner, one of the founding fathers of quantum mechanics and at the time a professor at Princeton University, suggested that hydrogen, an inert molecular gas at ambient conditions, could turn into a metallic solid, similar to lithium or sodium, at sufficiently high pressure. Wigner's proposal implied a remarkable complexity for "element one," the simplest chemical entity, one electron bound to one proton... Jupiter's magnetic field, first measured by Voyager spacecraft, is ten times stronger than Earth's, and its pattern is considerably more complex. Part of this complexity could be accounted for if the source of the field lay much farther from the center, in relative terms, than does Earth's. Wigner's prediction of metallic hydrogen was based on a simplified analysis of the electronic ground state, but the pressure he calculated for the transition to the metallic state, about 250,000 atmospheres, corresponded to a depth of less than one-twentieth of the planetary radius of Jupiter. In other words, most of the solar system's largest gas giant had to be in a metallic state -- although the metallic hydrogen would have to be a fluid rather than a solid to provide dynamo action... The fact is that the Earth's core is not pure iron but contains about 10 percent (by weight) of other constituents. If you compare the density of the outer core that is derived from seismological data with that of pure iron shocked to comparable pressures and temperatures, the core's density turns out to be about 10 percent lower. Even when the melting temperature of pure iron is accurately known at 2 million to 4 million atmospheres of pressure, we will still have to make a correction for the effect of contaminants. Alloying often decreases the freezing temperature of a material; this is why ice can be melted by putting salt on top of it. The actual freezing temperature at the innerâ€“outer core boundary may therefore be 1,000 kelvins or so lower than that of pure iron.

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