Ripples in Saturn’s rings have revealed that—far from having the stony heart most scientists expected—the planet’s innards are more like a slushie, National Geographic reports. The composition of Saturn’s core has long been a mystery. But planetary scientists recently realized that its rings—icy chunks that are pushed and pulled by the planet’s forces—can work like a seismograph, capturing the planet’s natural vibrations with visible ripples. Now scientists have figured out that one wave pattern in particular, on the “C ring,” records oscillations coming from deep in the heart of the planet. When scientists analyzed this wave, they found that Saturn’s innermost layer is likely a slushball of ice, rock, and gas, making up a whopping 60% of its radius, they report this week in Nature Astronomy. The core is so big that the remaining solid material equals the mass of 17 Earths.