Planetary-mass object

Planetary-mass objects are super cool space things! They are big enough to be round, like a ball, because their own gravity pulls them into a sphere. Think of a giant, cosmic bowling ball! But they aren't quite big enough to be stars, which have fiery furnaces inside them. They are like the in-betweeners of space, not quite planets, not quite stars.

These round space travelers can be born in different ways. Some are planets that orbit a star, just like Earth! Others are dwarf planets, which are a bit smaller. Some might be moons that are so big they act like planets. And some are lonely wanderers, called free-floating planets, that got kicked out of their star's family and now drift through space all by themselves.

The most important thing about a planetary-mass object is its shape. Its gravity is strong enough to make it perfectly round, like a balloon filled with water. This is called hydrostatic equilibrium. It's like when you blow up a balloon, the air inside pushes out evenly, making it round. These objects are also not hot enough to start burning like a star.

Planetary-mass objects are everywhere! Our own Earth is one. There are also dwarf planets like Pluto. Some are even moons orbiting giant planets, like Jupiter's moon Ganymede. And the most mysterious ones are the free-floating planets, which are like cosmic orphans, roaming the dark, empty spaces between stars without a parent star to call home.