Rocky planets orbiting distant stars may not necessarily have the same basic type of chemical or mineral composition as Earth, researchers from the Carnegie Institute of Science, the University of Chicago and Stony Brook University claim in a recently published study.
Writing in the journal Scientific Reports, Carnegie’s Sergey Lobanov, Nicholas Holtgrewe, and Alexander Goncharov demonstrated that the interiors of these far-off worlds may have different magnesium compounds than those commonly found on our home planet.
Along with oxygen, magnesium is one of the most abundant elements in the Earth’s mantle, the researchers explained. However, that doesn’t mean that other rocky planets would have a similar mantle mineralogy, as the composition of these planets are likely every bit as different from one another as their respective stars are from each other.
For instance, some stars that are home to rocky worlds have been found to have elevated levels of oxygen. This in turn could make the element more abundant in the interior of the planets, as the chemical makeup of a star has a direct impact on the chemical makeup of every planet that formed around it.
Proving MgO2 can synthesize under the right conditions
If it is possible for a planet to be more oxidized than Earth, this could also have an impact on the various compounds found in its interior as well. The researchers focused on the abundance of two magnesium compounds – magnesium oxide (MgO) and magnesium peroxide (MgO2).
MgO, they said, is known to be extremely stable, even under high pressures, and is not reactive under the conditions found in the Earth’s lower mantle. MgO2, on the other hand, can be formed in the laboratory under high-oxygen concentrations but tends to be unstable when heated, which would be the case in the interior of a forming rocky planet.
Building on previous theoretical calculations, Lobanov’s team used a laser-heated, diamond-anvil cell to bring small samples of magnesium oxide and oxygen to different pressure levels in order to mimic planetary interiors, determining whether or not it is possible to synthesize stable magnesium peroxide under such conditions.
They exposed MgO2 to ambient pressure 1.6 million times normal atmospheric pressure (0-160 gigapascals) and temperatures of more than 3,140 degrees Fahrenheit (2,000 Kelvin), and discovered that at under about 950,000 times normal atmospheric pressure (96 gigapascals) and at temperatures of 3,410 degrees Fahrenheit (2,150 Kelvin), MgO reacted with oxygen to form magnesium peroxide.
Lobanov: Exoplanet mineralogy may be vastly different than Earth’s
“Planetary physical properties are dependent on its composition,” Dr. Lobanov told redOrbit via email. “Our study is just an example of how exoplanet deep mineralogy may be different from our Earth. In fact, we may think of many new minerals that for some reasons are absent on Earth. MgO2 may be one of the most abundant minerals on a planet where oxygen is more abundant than on our Earth, but we don’t really know how abundant such oxidized planets are.”
“As we discover more and more about exoplanets it would become increasingly interesting to explore how unique our Earth is,” he added. “As of now, it really seems that there are a lot more types of planets than we have in Solar System. One of the key questions is how planetary interiors composed of yet unknown minerals control some planetary features we are used to on Earth such as plate tectonics and life, for example.”
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Feature image: Kepler 22b artist concept. Credit: Thinkstock
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