The physics and chemistry that takes place deep inside our planet are fundamental to the existence of life as we know it. But what forces act in the interior of distant worlds, and how do these conditions affect their habitability?
New work led by the Carnegie Earth and Planetary Laboratory uses lab simulation methods to reveal a new crystal structure that has major implications for our understanding of the interiors of large, rocky exoplanets. Their findings have been previously published Proceedings of the National Academy of Sciences.
Rajkrishna Dutta, lead author from Carnegie University, explained, “Our planet’s internal dynamics are essential to maintaining a surface environment in which life can thrive — driving the geodynamo that creates our magnetic field and shapes the composition of our atmosphere.” “Conditions found in the depths of large, rocky exoplanets such as super-terrestrial planets would be even more extreme.”
Silicate minerals make up most of the Earth’s layers and are believed to be a major component of the interiors of other rocky planets as well, based on calculations of their density. On Earth, structural changes occur in the silicates below high pressure Temperature conditions define major boundaries deep in the Earth’s interior, such as those between the upper and lower mantle.
The research team – which included Sally John Tracy of Carnegie, Ron Cohen, Francesca Mussi, Kai Lu and Jing Yang, as well as Pamela Burnley of the University of Nevada Las Vegas, Dean Smith and Yu Ming of the Argonne National Laboratory and Stella Chariton and Can Vitaly Brakabenka of the University of Chicago Thomas Duffy of Princeton University is interested in investigating the emergence and behavior of new forms of silicates under conditions that mimic those on distant worlds.
“For decades, Carnegie researchers have pioneered recreating the inner conditions of planets by placing small samples of material under enormous pressures and high temperatures,” Duffy said.
But there are limitations to scientists’ ability to recreate the internal conditions of exoplanets in the laboratory. Theoretical modeling indicated the emergence of new phases of silicate under the pressures expected to exist in the mantles of rocky exoplanets that are at least four times the mass of Earth. But this shift has not yet been noticed.
However, germanium is a good alternative to silicon. The two elements form similar crystal structures, but germanium induces a transition between chemical phases at lower temperatures and pressures, which can be more controlled in laboratory experiments.
Working with Magnesium Granite, Mg2geo4similar to one of the most abundant mantle silicate mineralsIn this article, the team was able to gather information about the possible minerals of the super-Earths and the large rocky exoplanets.
Under about two million times normal atmospheric pressure, a new phase appeared with a distinct crystal structure comprising germanium bonded to eight oxygens.
“The most interesting thing to me is that magnesium and germanium, which are two very different elements, replace each other in the structure,” Cohen said.
Under ambient conditions, most silicates and germaniums are organized in what is called a tetrahedral structure, one central silicon or germanium bonded to four other atoms. However, under extreme conditions, this can change.
Tracy explained that “the discovery that under extreme pressures, silicates could take on a structure geared toward six bonds, rather than four, was a total game-changer in terms of scientists’ understanding of deep Earth dynamics.” “The discovery of an eightfold trend could have similarly revolutionary implications for how we think about the dynamics of the inner exoplanet.”
Rajkrishna Dutta et al, Eight-stage coordinated hypertensive disorder of Mg2geo4: analogue of super ground cloaks, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2114424119
Carnegie Institution for Science
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