What's happening in the depths of distant worlds?
Discovery could have revolutionary implications for how we think about
the dynamics of exoplanet interiors

Date:
March 1, 2022
Source:
Carnegie Institution for Science
Summary:
The physics and chemistry that take place deep inside our planet
are fundamental to the existence of life as we know it. But what
forces are at work in the interiors of distant worlds, and how do
these conditions affect their potential for habitability? New work
uses lab-based mimicry to reveal a new crystal structure that has
major implications for our understanding of the interiors of large,
rocky exoplanets.



FULL STORY ==========================================================================
The physics and chemistry that take place deep inside our planet are fundamental to the existence of life as we know it. But what forces are
at work in the interiors of distant worlds, and how do these conditions
affect their potential for habitability?

==========================================================================
New work led by Carnegie's Earth and Planets Laboratory uses lab-based
mimicry to reveal a new crystal structure that has major implications
for our understanding of the interiors of large, rocky exoplanets. Their findings are published by Proceedings of the National Academy of Sciences.

"The interior dynamics of our planet are crucial for maintaining a
surface environment where life can thrive -- driving the geodynamo that
creates our magnetic field and shaping the composition of our atmosphere," explained Carnegie's Rajkrishna Dutta, the lead author. "The conditions
found in the depths of large, rocky exoplanets such as super-Earths would
be even more extreme." Silicate minerals make up most of the Earth's
mantle and are thought to be a major component of the interiors of other
rocky planets, as well, based on calculations of their densities. On
Earth, the structural changes induced in silicates under high pressure
and temperature conditions define key boundaries in Earth's deep interior,
like that between the upper and lower mantle.

The research team -- which included Carnegie's Sally June Tracy, Ron
Cohen, Francesca Miozzi, Kai Luo, and Jing Yang, as well as Pamela
Burnley of the University of Nevada Las Vegas, Dean Smith and Yue Meng
of Argonne National Laboratory, Stella Chariton and Vitali Prakapenka of
the University of Chicago, and Thomas Duffy of Princeton University --
was interested in probing the emergence and behavior of new forms of
silicate under conditions mimicking those found in distant worlds.

"For decades, Carnegie researchers have been leaders at recreating the conditions of planetary interiors by putting small samples of material
under immense pressures and high temperatures," said Duffy.



==========================================================================
But there are limitations on scientists' ability to recreate the
conditions of exoplanetary interiors in the lab. Theoretical modeling
has indicated that new phases of silicate emerge under the pressures
expected to be found in the mantles of rocky exoplanets that are at
least four times more massive than Earth. But this transition has not
yet been observed.

However, germanium is a good stand-in for silicon. The two elements
form similar crystalline structures, but germanium induces transitions
between chemical phases at lower temperatures and pressures, which are
more manageable to create in laboratory experiments.

Working with magnesium germanate, Mg2GeO4, analogous to one of the
mantle's most abundant silicate minerals, the team was able to glean information about the potential mineralogy of super-Earths and other
large, rocky exoplanets.

Under about 2 million times normal atmospheric pressure a new phase
emerged with a distinct crystalline structure that involves one germanium bonded with eight oxygens.

"The most interesting thing to me is that magnesium and germanium, two
very different elements, substitute for each other in the structure,"
Cohen said.

Under ambient conditions, most silicates and germanates are organized in
what's called a tetrahedral structure, one central silicon or germanium
bonded with four other atoms. However, under extreme conditions, this
can change.

"The discovery that under extreme pressures, silicates could take on
a structure oriented around six bonds, rather than four, was a total game-changer in terms of scientists' understanding of deep Earth
dynamics," Tracy explained.

"The discovery of an eightfold orientation could have similarly
revolutionary implications for how we think about the dynamics of
exoplanet interiors." This research was supported by the U.S National
Science Foundation, the U.S.

Department of Energy, the Gauss Centre for Supercomputing
and the endowment of the Carnegie Institution for Science, ========================================================================== Story Source: Materials provided by
Carnegie_Institution_for_Science. Note: Content may be edited for style
and length.


========================================================================== Related Multimedia:
* Illustration_of_potential_mineralogy_of_super-Earths ========================================================================== Journal Reference:
1. Rajkrishna Dutta, Sally June Tracy, R. E. Cohen, Francesca Miozzi,
Kai
Luo, Jing Yang, Pamela C. Burnley, Dean Smith, Yue Meng, Stella
Chariton, Vitali B. Prakapenka, Thomas S. Duffy. Ultrahigh-pressure
disordered eight-coordinated phase of Mg2GeO4: Analogue for
super-Earth mantles.

Proceedings of the National Academy of Sciences, 2022; 119 (8):
e2114424119 DOI: 10.1073/pnas.2114424119 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220301131035.htm

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