Jules Verne almost had it right back in 1864. In Journey to the Center of the Earth, a geologist and his team descend into a volcano in Iceland to explore Earth’s hidden metal core. But it turns out that visiting our planet’s center is and will remain an impossible feat for many human lifetimes: The core is hotter than the surface of the Sun and its pressure more than 3.5 million times that on Earth’s surface (see Physics Today, October 2023, page 12).

Just 12 years before Verne wrote his book, Annibale de Gasparis, an astronomer in Naples, Italy, discovered the 16th known asteroid, which he named Psyche. Since that time, astronomers have been observing how strongly Psyche’s gravity tugs on passing asteroids, bouncing radar waves off it, and measuring the spectrum of light reflected from its surface. Collectively, these observations now tell us that Psyche is...

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