The Exotic Behavior of Matter in the middle of Jupiter
The atom, with its single proton orbited by one electron, is arguably the only material out there. Elemental hydrogen can nonetheless exhibit extremely complex behavior — at megabar pressures,
for instance, it undergoes a transition from being an insulating fluid to being a metallic conductive fluid.
While the transition is fascinating simply from the purpose of view of condensed matter physics and materials science — liquid-liquid phase transitions are rather unusual
it also has significant implications for planetary science,
since liquid hydrogen makes up the inside of giant planets like Jupiter and Saturn also as brown dwarf stars.
Understanding the liquid-liquid transition is then a central part of accurately modeling
the structure and evolution of such planets and standard models generally assume a pointy transition between the insulating molecular fluid
therefore the conducting metallic fluid.
This sharp transition is linked to a discontinuity in density
thus a transparent border between an inner metallic mantle and an outer insulating mantle in these planets.
While scientists have made considerable efforts to explore and characterize this transition also as dense hydrogen’s many unusual properties
including rich and poorly understood solid polymorphism, anomalous melting line,
therefore the possible transition to a superconducting state laboratory investigation is complicated
due to the necessity to make a controllable high and temperature environment also on confine hydrogen during measurements.
Experimental research has then not yet reached a consensus
on whether the transition is abrupt or smooth and different experiments have located
the liquid-liquid transition at pressures that is the maximum amount as 100 gigapascals apart.
“The quite experiment that you simply got to be ready to do to study a cloth within the same range of pressures
that you find on Jupiter is very non-trivial”
” Ceriotti said.
“As a result of the constraints, many various experiments are performed,
with results that are very different from one another .”
Though modeling techniques introduced within the last decade have allowed scientists to raised understand the system,
the large computational expense involved in essentially solving the quantum mechanical problem for the behavior of hydrogen atoms has meant that these simulations were necessarily limited in time,
to a scale of a couple of picoseconds, and to a scope of just a couple of hundred atoms.
The results here have also been mixed.
In order to look at the matter more thoroughly, Ceriotti and colleagues Bingqing Chen at the University of Cambridge and Guglielmo Mazzola at IBM Research Zurich used a man-made neural specification
to construct a machine learning potential.
supported a little number of very accurate (and time-consuming) calculations of the electronic structure problem,
the cheap machine-learning potential allowed for the investigation of hydrogen phase transitions for temperatures between 100 and 4000 K, and pressures between 25 and 400 gigapascals,
with converged simulation size and time.
that it might have taken to run traditional simulations for solving the quantum mechanical problem.
The resulting theoretical study of the phase diagram of dense hydrogen allowed the team to breed the re-entrant melting behavior.
therefore the polymorphism of the solid phase.
Simulations supported the machine learning potential showed, contrary to the common assumption that hydrogen undergoes a first-order phase change, evidence of continuous metallization within the liquid.
This successively not only suggests a smooth transition between insulating and metallic layers in giant gas planets, it also reconciles existing discrepancies between both lab and modeling experiments.
“If high-pressure hydrogen is supercritical, as our simulations suggest,
there’s no sharp transition
where all the properties of the fluid have a sudden jump,” Ceriotti said.
“Depending on the precise property you probe,
therefore the way you define a threshold, you’d find the transition to occur at a special temperature or pressure.
this might reconcile a decade of controversial results from high experiments.
Different experiments have measured slightly various things
that they haven’t been ready to identify the transition at an equivalent point
because there’s no sharp transition.”
In terms of reconciling their results with some earlier modeling that indeed identified a pointy transition,
Ceriotti says that they might only observe a clear-cut jump in properties
when performing small simulations, which in those cases they might trace the jump to solidification,
instead of to a liquid-liquid transition.
The sharp transition should be observed then preferably be understood
as an artifact of the restrictions of using simulations supported traditional physics-based modeling.
The machine learning approach has allowed
the researchers to run simulations
that are typically between 4 and 10 times larger and a number of other 100s of times longer.
this provides them a way better overview of the whole process.
While it had been applied during this particular paper to a problem linked to planetary science, an equivalent technology is often applied to any problem in materials science or chemistry,
“This may be a demonstration of a technology
that permits simulations to urge into a regime that has been impossible to succeed in,” Ceriotti said.
“The same technology that we could use to know better
the behavior of planets also can be wont to design better drugs or more performing materials.
There really is that the potential for a simulation-driven change of the way
we understand the behavior of every day, also as exotic, matter.”