Scientists discover the first building blocks in the formation of super-Earths

Scientists observed for the first time how atoms in a magnesium oxide molecule change and dissociate under extremely harsh conditions, and gained new insights into this important mineral in the Earth's mantle that is known to influence the formation of planets

Researchers have shown through high-energy laser experiments that magnesium oxide is probably the first mineral to solidify in the formation of super-Earths and its critical influence in geophysical development.

Scientists observed for the first time how atoms in magnesium oxide change and dissociate under extremely harsh conditions, and gained new insights into this important mineral in the Earth's mantle that is known to influence the formation of planets.

Experiments with a high-energy laser - which applied heat and pressure to tiny crystals of the mineral of the type found deep within the mantle of a rocky planet - show that the compound may be the earliest mineral to solidify from magma oceans in the formation of extrasolar planets of the "super-Earth" type.

"Magnesium oxide may be the most important solid controlling the thermodynamics of super-young Earths," said John Weeks of Johns Hopkins University, who led the study. "If it has this very high melting temperature, it will be the first solid to form when a hot rocky planet starts to cool and its interior separates into a core and a mantle."

The findings indicate that the way magnesium oxide changes from one form to another can have important consequences for the factors that determine whether a young planet will be a snowball or molten rock, develop water oceans or an atmosphere, or have a mixture of these properties.

"On super-terrestrial Earths, where this material will be a large component of the mantle, its variation will contribute significantly to the rate of heat transfer in the interior, which will determine how the interior and the rest of the planet form and deform over time," Weeks said. "You can think of this as a measure of the interiors of these planets, because this is going to be the material that controls their deformation, one of the most important building blocks in rocky planets."

Super Earths, larger than Earth but smaller than giants like Neptune or Uranus, are important targets in the study of extrasolar planets because they are common in other solar systems in the galaxy. Their composition can vary from gas to ice or water, but rocky super-Earths are expected to contain large amounts of magnesium oxide that can affect the star's magnetic field, volcanism and other important geophysical features as it does on Earth," Weeks said.

To mimic the extreme conditions the mineral might experience during planet formation, the team subjected small magnesium oxide samples to very high pressures using the Omega-EP laser facility. The scientists also shot X-rays and recorded how those rays bounced off the crystals to track how their atoms rearranged in response to the increasing pressures, noting specifically at what point they changed from solid to liquid. When pressed very hard, the atoms of minerals like magnesium oxide change their arrangement to withstand the crushing pressures.

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