How big can a rocky planet get?

A newly discovered rocky planet, 17 times the mass of ours, has been called the 'Godzilla of Earths. read more

An artist's illustration of the mega-Earth planet Kepler-10c, the"Godzilla of Earths" planet that is 2.3 times the size of Earth and 17 times heavier. The planet and its lava-world sibling Kepler 10b (background) orbit the star Kepler-10 about 570 light-years from Earth. Image released June 2, 2014. read more

We’ve seen that terrestrial planets can get smaller, with Mars and Mercury, and astronomers have detected larger terrestrial planets orbiting other stars. The largest known rocky planet is thought to be Gliese 436 c. This is probably a rocky world with about 5 Earth masses and 1.5 times our planet’s radius. read more

If it gets too big it will accumulate a thick hydrogen or helium atmosphere, becoming a gas giant. If you somehow restricted the supply of hydrogen and helium, as well as water ice, then the planet will stop growing when it runs out of material. read more