Laser Models Planet Cores That Could Crush Diamond

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Mother Nature uses the same collection of building blocks throughout the universe but gathers the elements in almost unimaginably different ways.

Conventional wisdom says that moons originate from their planets, so imagine everyone's surprise when data emerged suggesting that Saturn's moon Titan might be older than Saturn itself.

Take carbon, for example, the fourth most common element in the universe, which not only is a key component of all life on Earth, but also coveted as crystal gems when pressure-cooked inside the planet.

What happens to carbon -- and other solid materials -- when the pressure is even greater, such as what exists in the cores of Jupiter, Saturn and giant planets beyond the solar system?

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Until now, scientists’ only insight came from computer models. New work at the U.S. National Ignition Facility, nicknamed NIF, which houses the world’s largest laser, is providing the first hard evidence.

Scientists this week report they have compressed diamond to the density of lead -- about 50 million times the pressure of Earth’s atmosphere and 14 times the pressure in the planet’s core -- without the high heating that liquefies solids.

The experiment, reported in this week’s Nature, is the first of many planned to probe the behavior of materials at pressures more native to Neptune than Earth.

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“With NIF we can go way beyond traditional techniques,” Princeton University geoscientist Thomas Duffy told Discovery News. “That opens the door to start to do experiments under conditions that, in the past all we had were theoretical calculations for.”

The core of Jupiter, for example, is between 50 million and 70 million Earth atmospheres, though scientists don’t know what it contains or how it formed, information that is key to filling a gap in understanding how planets, big and small, come to exist.

“We can actually go to the pressures that are in Jupiter’s core. So for the first time we don’t have to rely just on theoretical calculations of what things might be like there, but we can actually test those calculations with experiments,” Duffy said.

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Early results already are surprising. The carbon atoms in the laser-zapped diamond did not transform their structure as predicted.

Carbon’s extraordinary strong and stable chemical bonds may not have had enough time to break down as expected during the laser blast, which lasted just 20 nanoseconds. Or there may be something peculiar to carbon that causes it to remain stable despite the availability of seemingly preferable, lower-energy arrangements, said theorist Chris Pickard with University College London’s Department of Physics and Astronomy.

“It’ll be interesting to see if the same thing happens in other materials,” Pickard told Discovery News.

Additional experiments are planned to get more details about the temperatures diamond reaches at 50 million atmospheres and beyond. Scientists also plan to put the squeeze on iron, which is expected to provide some unprecedented evidence for how rocky planets, like Earth, form.