The Z machine at Sandia National Laboratories is an extreme device. Its ring of capacitors fill a room about the size of two basketball courts. When they fire, they unleash an electrical pulse that, for a few billionths of a second, delivers more power than is generated by all the world’s power plants at any given moment. This pulse triggers a shockwave that subjects anything at the machine’s centre to pressures equivalent to those found deep inside giant gas planets and nuclear explosions.
Late last month, Alisha Clark, a mineral physicist at the University of Colorado in Boulder, harnessed the power of the Z machine to study something closer to home: Earth’s interior. Nature joined her to observe the final ‘shot’ taken with the machine in a multi-year project to better understand the origins of water on Earth.
This focus on Earth is unusual for the Z machine. Located on the Kirtland Air Force Base in Albuquerque, New Mexico, the device was originally built for testing materials to guarantee the reliability of the US stockpile of nuclear weapons without having to detonate bombs. That’s still mostly what it’s used for. But about 10% of the shots taken with the device each year are set aside for fundamental research.
Firing the machine requires months of preparation and input from more than a hundred people. Each shot takes a full day to set up and costs around US$250,000. As a result, few requests to use the machine are approved for researchers studying planets, and even fewer for people investigating Earth.
But the Z machine is crucial for Clark’s work. She suggests that during the early, chaotic days of Earth’s formation, melted rock inside the planet trapped and held onto water — counter to the origin story that geoscientists usually tell. “Earth is a sponge,” she told Nature.
To test this idea, Clark needed to simulate how melted rock behaves under the conditions near Earth’s core as it formed. And that’s where the Z machine came in.
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