Laser-Blasting Researchers Simulate Super-Earths

Using laser blasts, scientists have recreated the extreme temperatures and pressures found inside large rocky planets known as super-Earths as well as in icy giant planets such as Neptune and Uranus, shedding light on what the interiors of these exotic worlds are like.

The new findings suggest that the interiors of super-Earth exoplanets may consist of oceans of molten rock that generate magnetic fields, and that giant planets may contain solid, rocky cores, researchers say.

In the past 20 years or so, astronomers have confirmed the existence of more than 1,800 planets orbiting distant stars. The planets include types different from those seen in our own solar system — such as super-Earths, which are rocky planets up to 10 times as massive as Earth. [The Strangest Alien Planets]

Meet Earth’s cousin planet, Kepler 186f 0:58

The innards of super-Earths and giant planets experience much higher pressure than Earth's because they have more mass squeezing inward. However, it was uncertain what effects such conditions might have on the properties of silica and other ingredients typically found in planetary interiors, since it is difficult to generate such high pressures on Earth.

Until now, the highest pressure at which scientists had melted silica was about 100 gigapascals, which is roughly 1 million times the atmospheric pressure of Earth at sea level. Now scientists have exposed silica to a pressure of 500 gigapascals. That's comparable to the pressure that exists at the boundary of the core and mantle in a super-Earth that is five times Earth's mass. [Formation of Planets in a Protoplanetary Disk (Video)]

The researchers focused laser blasts on a dense form of silica known as stishovite — and found that at 500 gigapascals, the melting temperature of silica rises from around 3,000 degrees Fahrenheit (1,650 degrees Celsius) to about 14,480 degrees F (8,025 degrees C).

"The melting temperature of silica is similar to that of iron at those pressures," lead study author Marius Millot, a physicist at Lawrence Livermore National Laboratory in California, told "This suggests that in large, rocky exoplanets, we have magma oceans of liquid silicates coexisting with liquid iron, which is not something that has been considered before when modeling those planets."

The investigators found that high-pressure liquid stishovite was electrically conductive, which means it could generate magnetic fields.

Millot said the findings also suggest that silica is solid inside icy giants such as Neptune and Uranus as well as in gas giants such as Jupiter and Saturn.

The new study was published online Thursday in the journal Science.

— Charles Q. Choi,

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