Bizarre new planet is largest known rocky world, 40 times as massive as Earth. The bulky object—possibly the core of a failed gas giant—challenges what astronomers think about how planets form.

The exoplanet, L 98-59 c, is a hot, rocky world slightly larger than Earth that orbits a bright, young star about 35 light-years away from us. While the planet itself was discovered back in 2019 ...