Earth’s core isn’t just a boring, featureless ball of metal, it turns out. A recent study used seismic waves from earthquakes to make a 3D model of the center of our planet, and the researchers discovered that Earth’s inner core is a patchwork of different textures and densities. And there may even still be some liquid iron trapped inside.

The recent study was published in the journal Nature. Seismologist Guanning Pang and his colleagues used a worldwide network of seismic stations, originally built to watch for underground nuclear weapons testing, to watch seismic waves from earthquakes reflect off Earth’s inner core. It took about 2,455 strong earthquakes, measured over about 25 years, before the geologists had mapped enough reflected seismic waves to create a 3D model of our planet’s solid metal heart.

Making Indiana Jones look young again was (relatively) easy. The hard part? Doing the same for his latest enemy, a Nazi scientist played by Mads Mikkelsen.

“There was a desire that we didn't necessarily want him to look like a younger Mads Mikkelsen,” VFX supervisor Andrew Whitehurst tells Inverse.

“So we did a lot of concept arts and testing, to see what young Jurgen Voller [Mads Mikklesen’s character] looks like, rather than trying to make him look like Mads did,” says Whitehurst, who spent three years working on the movie. “It was a slightly different approach as we weren't trying to match something from the past exactly. We were trying to figure out and imagine what this character would look like as a younger man and then achieve that.”

That’s just one example of the ways that Disney, Lucasfilm, and Industrial Light and Magic pushed the boundaries of special effects technology in Indiana Jones and the Dial of Destiny. In the process, they invented a new type of technology, which the company calls ILM FaceSwap. To find out how it works (and a few more secrets from the making of Indy 5), Inverse spoke to Whitehurst along with ILM’s own VFX supervisor Robert Weaver and senior publicist Ian Kintzle. Here’s what we learned.