High-Pressure Phase Changes Could Play Role In Exoplanet Formation
February 12, 2012

High-Pressure Phase Changes Could Play Role In Exoplanet Formation

Phase transitions in liquid magmas at the pressure and temperature levels that exist deep within Earth-like planets could play a role in the formation of new worlds, according to a new research put forth by experts at California's Lawrence Livermore National Laboratory (LLNL).

According to a Friday UPI article, the process is similar to the way that graphite, when placed in high-pressure conditions, can transform into diamonds. In much the same way, the LLNL researchers assert that molten magnesium silicate could experience a similar change to become a denser liquid with increasing pressure.

The research, according to an LLNL press release, could provide new insight into how planets form.

"Phase changes between different types of melts have not been taken into account in planetary evolution models," lead scientist Dylan Spaulding, a graduate student at the University of California, Berkeley who conducted most of his thesis work at the Laboratory's Jupiter Laser Facility, said in a statement.

"But they could have played an important role during Earth's formation and may indicate that extra-solar 'Super-Earth' planets are structured differently from Earth," he added.

Spaulding and his colleagues determined that melts play an essential role in planetary evolution, and according to the UPI, it could possibly influence the thermal transport and convective processes that are essential to the formation of the core and mantle early on in a world's history.

The researchers said that a pressure-induced liquid-liquid phase separation in silicate magmas -- described by LLNL's Anne M. Stark as "similar to the difference between oil and vinegar“¦ they want to separate because they have different densities" -- could help explain the thermal-chemical evolution of the interiors of exoplanets.

"In the new research, however, the researchers noticed a sudden change between liquid states of silicate magma that displayed different physical properties even though they both have the same composition when high pressure and temperatures were applied," Stark wrote in the Laboratory's press release.

Spaulding and his team used both the Janus laser and University of Rochester's OMEGA laser to create powerful laser pulses to generate a shock wave through samples in an attempt to recreate the kind of extreme pressure and temperature that exist in the interior of exoplanets located outside of our solar system.

"By looking for changes in the velocity of the shock and the temperature of the sample, the team was able to identify discontinuities that signaled a phase change in the material," Stark wrote. "The team concluded that a liquid-liquid phase transition in a silicate composition similar to what would be found in terrestrial planetary mantles could help explain the thermal-chemical evolution of exoplanet interiors."

In addition to Spaulding, LLNL researchers Jon Eggert, Peter Celliers, Damien Hicks, Gilbert Collins and Ray Smith, as well as experts from the University of California, Berkeley, the Carnegie Institution of Washington and Howard University, worked on the study, which appears in the Feb. 10 edition of the journal Physical Review Letters, according to the Laboratory's press release.


Image Caption: An artist's conception of planet Kepler-22b, which orbits in a star's habitable zone -- the region around a star where liquid water, a requirement for life on Earth, could persist. The planet is 2.4 times the size of Earth.


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