Deep interior of Neptune, Uranus and Earth may contain solid ice
Washington, September 24 : In a bid to determine the melting temperature of ice in high
atmospheric pressures, scientists have found a sharp increase in the melting curves, which
opens up the possibility that water exists as a solid in the deep interior of planets such
as Neptune, Uranus and Earth.
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.
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.
"The sharp increase in the melting curves slope opens up the possibility that water
exists as a solid in the deep interior of planets such as Neptune, Uranus and Earth,"
Schwegler said.
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.
Determining the melting curve of water is important to many fields of science,
including physics, chemistry and planetary science.
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.
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.
"To accurately determine the melting temperature of water, we used a two-phase
simulation method that is designed to avoid the large super-heating and cooling effects
that are often present in single-phase heat-until-it-melts or squeeze-until-it-freezes
approaches," Schwegler said.
--ANI
