Thousands of kilometers below the earth’s surface, under extreme pressure and temperature, the planet’s core can be found. There is an inner core consisting of a dense iron-nickel sphere that rotates excessively within the outer core, where the iron and nickel are liquid.
These outer core conditions have now been recreated in the laboratory, by a team led by physicist Sebastian Merkel of the University of Lille in France – in such a way that scientists can observe the structural deformation of iron.
Not only does this have implications for understanding our planet, but it could help us better understand what happens when pieces of iron collide in space.
“We don’t create completely substantive conditions internally,” Physicist Arianna Gleeson says: From the US Department of Energy’s SLAC National Accelerator Laboratory. “But we’ve reached the state of the planet’s outer core, which is very cool.”
Under normal Earth conditions, the crystalline structure of iron is A cube grid. The atoms are arranged in a lattice, with an atom at the corner of each cube, and one in the middle. When iron is compressed under very high pressure, this lattice deforms and deforms into hexagonal structure. This allows more atoms to be packed into the same volume of space.
But it’s hard to say what happens even at higher pressures and temperatures – like what happens at the Earth’s core. However, in recent years laser technology has advanced to the point where, in a laboratory environment, small samples can be exposed to extreme conditions, such as the pressure and temperature found in white dwarfs.
The team at SLAC deployed two lasers. The first is an optical laser, which shoots a microscopic sample of iron and exposes it to a shock that creates extreme pressure and heat.
The pressure of the Earth’s outer core ranges from 135 to 330 gigapascals (1.3 to 3.3 million atmospheres), and temperatures between 4,000 and 5,000 K (3727 to 4727 ° C, or 6,740 to 8,540 ° F). Pressures and temperatures up to 4070 K .
The next, and arguably the most difficult, part is measuring the atomic structure of iron during this process. For this purpose, the team used an X-ray-free Linac Coherent Light Source (LCLS) laser, which examines the sample as it shoots the laser beam.
“We were able to take measurements in a millionth of a second,” kata Gleeson. “Freezing atoms where they are in nanoseconds is really fun.”
The resulting images, grouped into sequences, reveal that iron responds to the additional stress induced by this condition with twinning. This occurs when the crystal lattice becomes so compact that some of the lattice points are divided by several crystals symmetrically.
(S. Merkel / University of Lille, France)
For iron in the outer core condition, this means the arrangement of atoms is pushed so that the hexagon rotates about 90 degrees. This mechanism allows the metal to hold its ends, the researchers said.
“Twinning allows iron to become very strong – stronger than we thought – before starting to flow plastically over a longer time scale,” kata Gleeson.
Now that we know how iron behaves under these conditions, this information can be fed into models and simulations. This has important implications for the way we understand space collisions, for example. Earth’s core lies neatly deep within a planet, but there are asteroids so metallic that we think it’s the bare, exposed core of the planet interfering with their formation.
These objects can collide with other objects that can damage the iron structure inside. Now we have a better idea of how this happened. And of course, we now know more about our planet.
“The future is bright now that we have developed a way to make these measurements,” kata Gleeson.
“Now we can give a thumbs up, and a thumbs up for some very basic physical models of deformation mechanisms. That helps build some predictive power that we don’t have for modeling how materials respond under extreme conditions.”
Search published in physical review message.
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