About 730 light-years away, not far on the scale of our galaxy, an utterly bizarre planet orbits a sun-like star. Big, dense, and tightly tethered to its home star, the planet is unlike anything astronomers have yet seen—either in our own solar system or afar.

The roasted world known as TOI-849b is the most massive rocky planet ever observed, with as much as 40 Earths’ worth of material crammed inside. Perplexingly, TOI-849b’s tremendous bulk suggests that it should be a giant, gassy world like Jupiter, yet it has almost no atmosphere. Explaining how such a world emerged challenges what scientists understand about how planets grow.

“It’s very difficult to make a planet as massive and dense as TOI-849b without it becoming a