We all know what water is. And what rock is. The difference is crystal clear. Well, here on Earth it is.
But on other worlds? The difference might not be so clear.
Among the hundreds of billions of stars in the Milky Way are who-knows-how-many exoplanets. Some number of them will be ocean worlds, completely covered in water with little to no land-masses. And most of them will likely be much larger than Earth. These planets can host oceans up to 1,000 km thick, according to scientists, and all that water is pressing down on a rocky mantle.
Scientists have a bunch of questions about these type of planets. Could life develop on these worlds? If so, what kind of life? Could this type of world even support life, or is exposed land a critical part of a world’s biogeochemistry, like here on Earth?
A team of researchers led by Arizona State University wanted to do more than just think about them. In an effort to better understand these worlds, and to make some progress on these questions, they recreated a water-world in their lab. Sort of.
The results of their work were just published in the Proceedings of the National Academy of Sciences of the USA. The paper’s title is “Large H2O solubility in dense silica and its implications for the interiors of water-rich planets.” Lead author is Dan Shim, associate professor at ASU, and head of the University’s Lab for Earth and Planetary Materials.
The team of researchers used the Advanced Photon Source lab at the Department of Energy’s Argonne National Laboratory. That may seem incongruous—using an x-ray lab to study planets—but it worked. As lead author Dan Shim said in a press release, “People hardly think about astrophysics when talking about an X-ray facility. But we can use a facility like the APS to understand an object too distant for us to see.”
In the lab, the researchers re-created the extreme properties of large ocean worlds. These planets can have mantles of rock, with vast amounts of water above them, pressing down on them with intense pressure. That crushing pressure also creates intense heat.
“Determining the geology of exoplanets is tough, since we can’t use telescopes or send rovers to their surfaces,” Shim said. “So we try to simulate the geology in the lab.”
The team placed samples of silica, or silicon dioxide, in between special diamonds in a device called a diamond anvil cell. They then compressed the samples to…