The crystal structure of magnesium peroxide, MgO2, courtesy of Sergey Lobanov, created using K. Momma’s program for drawing crystal structures. Credit: Sergey LobanovÂ
New Carnegie research demonstrates different magnesium compounds could be abundant inside other planets as compared to Earth. O and Mg are the two most-abundant elements in Earth’s mantle. However, when predicting the chemical compositions of rocky, terrestrial planets outside of our own Solar System, they shouldn’t assume that other rocky planets would have Earth-like mantle mineralogy, according to Carnegie’s Sergey Lobanov, Nicholas Holtgrewe, and Alexander Goncharov.
Eg. elevated oxygen contents have been observed in stars that host rocky planets. As such, oxygen may be more abundant in the interiors of other rocky planets, because the chemical makeup of a star would affect the chemical makeups of the planets that formed around it. If a planet is more oxidized than Earth, then this could affect the composition of the compounds found in its interior, too, including magnesium compounds.
MgO is known to be stable even under very high pressures. And it isn’t reactive under the conditions found in Earth’s lower mantle. Whereas magnesium peroxide, MgO2, can be formed in the laboratory under high-oxygen concentrations, but it is highly unstable when heated, as would be the case in a planetary interior. Previous calculations had indicated magnesium peroxide would become stable under high-pressure conditions. Taking that idea one step further, the team set out to test whether stable magnesium peroxide could be synthesized under extreme conditions mimicking planetary interiors.
Using a laser-heated, diamond-anvil cell, they brought very small samples of magnesium oxide and oxygen to different pressures meant to mimic planetary interiors, from ambient pressure to 1.6 million times normal atmospheric pressure (0-160 gigapascals), and heated them to temps >3,140F (2,000 K). Under ~950,000 times normal atmospheric pressure (96 gigapascals) and at temperatures of 3,410F (2,150 K), MgO reacted with O to form MgO2. “Our findings suggest that magnesium peroxide may be abundant in extremely oxidized mantles and cores of rocky planets outside our Solar System,” said Lobanov.
“These findings provide yet another example of the ways that high-pressure laboratory experiments can teach us about not only our own planet, but potentially about distant ones as well,” added Goncharov.
Because of its chemical inertness, MgO has also long been used as a conductor that transmits heat and pressure to an experimental sample.
http://www.eurekalert.org/pub_releases/2015-09/ci-dpi083115.php
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