In a laboratory where lasers press a tiny crystal of magnesium oxide beyond anything previously attempted, researchers have found that the material does not forget the direction from which it was squeezed, even under conditions that theory had assumed would erase such differences. The common rock that likely forms much of planetary interiors, it turns out, still carries a memory of its geometry at extremes of heat and pressure. This quiet correction bears on how we imagine the hidden depths of worlds we will never visit, where heat moves and magnetic fields are born.
Squeezing Magnesium Oxide From Different Directions Reveals New Clues to Planetary Interiors
The direction of the squeeze turned out to matter after all
Mark
Why does the direction of compression matter so much?
Mimi
Older theory said that at extreme pressure and temperature, the crystal's orientation stops mattering. These experiments showed the response changed with direction, so that assumption doesn't hold.
Mark
And the melting result?
Mimi
The MgO melted at 572 gigapascals and 13,000 kelvin, a record for a known material. Earth's center is about 360 gigapascals and 6,000 kelvin, so this goes well beyond it.
Luke
Careful with the word record. It's an experimental record, set with lasers on a small crystal, not a measurement of anything inside a planet.
Mark
Fair. What does it tell us about super-Earths?
Mimi
MgO there can become a conductive liquid in the mantle, which could give magnetic fields much stronger than Earth's. Knowing where it melts helps decide that.
Luke
That's a possibility the researchers describe, not something observed. Nobody has measured a super-Earth's mantle.
Mark
Anything unclear in the reporting?
Luke
Yes. The description of exactly which compression direction gave which result is muddled in the source. Only the general finding is solid: directions differed, and two produced disordered growth behind the shock wave.
Mimi
And Wicks's point stands: knowing solid versus liquid shapes how planets move heat and evolve.
Der Puls
- A small cube of magnesium oxide was driven to 572 gigapascals and 13,000 kelvin, a new experimental extreme that outruns the conditions near Earth's center.
- The crystal responded differently depending on the direction of compression, contradicting long-held theory that extreme pressure should wash such differences away.
- Two of the compression directions produced disordered, irregular growth behind the shock wave, unsettling assumptions used in planetary models.
- The team's three-part series, now extended with this record-setting melt, is steadily narrowing where MgO stays solid and where it becomes liquid.
- Models of super-Earth mantles and gas giant cores may need revision, since these shifts could govern whether magnetic fields and heat flow take hold.
In a laboratory where lasers press a tiny crystal of magnesium oxide beyond anything previously attempted, researchers have found that the material does not forget the direction from which it was squeezed, even under conditions that theory had assumed would erase such differences. The common rock that likely forms much of planetary interiors, it turns out, still carries a memory of its geometry at extremes of heat and pressure. This quiet correction bears on how we imagine the hidden depths of worlds we will never visit, where heat moves and magnetic fields are born.
At Lawrence Livermore National Laboratory and Johns Hopkins University, researchers have aimed lasers at a small cube of magnesium oxide and pushed it harder and hotter than anyone has pushed this kind of crystal before. The work, published in Physical Review X, is the latest step in a twelve-year effort to understand how one of the most common rocky materials in planetary interiors behaves when conditions far exceed those inside Earth.
Scientists have long reasoned that magnesium and silicon are the chief building blocks of planets, and that under Earth's mantle pressures they form magnesium oxide. What happens to that material on gas giants and larger rocky worlds called super-Earths, where the extremes differ, has remained an open question. This paper is the third in a series, following studies from 2015 and 2024.
This time the crystal reached 572 gigapascals and 13,000 kelvin, roughly 23,300 degrees Fahrenheit, well beyond the conditions near Earth's center. At that point it melted, setting a new experimental record for a known material. The team also varied the direction of compression, and the crystal responded differently depending on the orientation. Theory had predicted that such direction would stop mattering at these extremes, so the finding challenges an assumption planetary models have relied on.
Dr. June Wicks of Johns Hopkins, a co-author, explained that the results help pin down where magnesium oxide stays solid and where it turns liquid, which in turn shapes how planets move heat and evolve. On super-Earths, the material may become a conductive liquid within the mantle, possibly generating magnetic fields far stronger than Earth's. In gas giants like Jupiter and Saturn, it may be solid or liquid deep in the core depending on temperature.
The work points toward better models of heat and magnetism inside distant worlds, and those models may now need to account for the direction in which these crystals are squeezed.
Researchers at Lawrence Livermore National Laboratory and Johns Hopkins University have fired lasers at a small cubic crystal of magnesium oxide, squeezing it harder and hotter than anything of its kind has been pushed in an experiment before. The results, published in Physical Review X, bear on a question that has occupied the team for twelve years: how does the most common rocky material in planetary interiors behave when conditions get far more extreme than anything inside Earth?
The background is straightforward. Scientists study planetary interiors through a mix of approaches: Earth as an analog, computer models, meteorites, and data gathered from other worlds. From that work they have concluded that magnesium and silicon are the most abundant building blocks of planets. Under the pressures found in Earth's mantle, they form magnesium oxide, or MgO, crystals. The open question is what happens to the same material on gas giants and on larger rocky exoplanets known as super-Earths, where pressures and temperatures differ.
The new paper is the third in a series, following a 2015 study in Physical Review Letters and a 2024 study in Science Advances. In this round, the team used lasers to compress a cubic MgO crystal and mimic planetary interior conditions. The peak was 572 gigapascals and 13,000 kelvin, about 12,927 degrees Celsius or 23,300 degrees Fahrenheit. For comparison, conditions near Earth's center are roughly 360 gigapascals and 6,000 kelvin, or about 5,727 degrees Celsius.
The team also varied the direction of the compression, which turned out to matter. Longstanding theory held that at such extremes, the direction of the squeeze should not make a difference. The experiments say otherwise. The cube was compressed along three orientations relative to its geometry, including perpendicular to a cube face and along diagonals, and the crystal responded differently depending on which was used. The source's account of the specific orientation-by-orientation results is garbled, but it states that two of the directions produced disordered, irregular crystal growth behind the shock wave created by the compression.
The experiments also found that the MgO melted at 572 gigapascals and 13,000 kelvin. That sets a new experimental record for pressure and temperature for a known material.
Dr. June Wicks, a professor in Johns Hopkins' Department of Earth and Planetary Sciences and a co-author, described why this matters. Magnesium oxide, she said, is an important ingredient in understanding planetary interiors, and the experiments help pin down where it stays solid and where it turns liquid. That in turn affects how planets move heat and evolve.
The stakes differ by planet type. Rocky bodies have a crust, mantle and core. On Earth, which has a liquid outer core and a rocky inner core, MgO forms near the base of the mantle, close to the core-mantle boundary. On super-Earths, MgO can become a conductive liquid within the mantle itself, which could produce magnetic fields much stronger than Earth's. On gas giants such as Jupiter and Saturn, MgO deep in the cores can be solid or liquid depending on temperature.
What the work points toward is better models of how heat and magnetism arise inside worlds beyond our own, with the direction-dependence of crystal response now something those models may need to account for.
Bemerkenswerte Zitate
Magnesium oxide is an important ingredient in our understanding of planetary interiors; these experiments help determine where it stays solid and where it becomes liquid.— Dr. June Wicks, Johns Hopkins University
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