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 gas giant,” David Armstrong, an exoplanet researcher at the University of Warwick and lead author of a study reporting the new planet today in the journal Nature, says in an email. “Something in that standard process went wrong.” Instead, Armstrong and his colleagues think the world is the exposed, airless core of a giant planet that should have outgrown Jupiter.

“These are the objects that push theory further, and make the fields of exoplanets and planetary science so exciting,” study co-author Ravit Helled of the University of Zurich says in an email.

“It’s definitely weird!” adds Jonathan Fortney, director of the Other Worlds Laboratory at the University of California Santa Cruz, who wasn’t involved in the observations. “But I’m not sure what it’s telling us.”

There are four terrestrial planet Mercury, Venus , earth ,mass :)