This Newly Discovered Exoplanet Is Denser Than Lead – SlashGear

The discovery of such a massive exoplanet is particularly interesting because it helps define what the upper bounds of a planet can be in terms of size and mass. There is a type of object called a brown dwarf, which is halfway between a planet and a star. The defining feature of a star is that it undergoes nuclear fusion in its core, which produces light and heat and is what makes it glow brightly. Brown dwarfs don’t have enough mass to create fusion of hydrogen into helium in their cores, so they aren’t really like stars.

However, brown dwarfs can sometimes fuse other elements like deuterium or lithium, so they aren’t really like planets either. They are sometimes referred to as failed stars or as substellar objects to reflect this ambiguity, and they typically have a mass of between 13 and 80 times the mass of Jupiter.

This newly discovered planet is right on the border of being a brown dwarf. It has a mass of 12.89 times that of Jupiter, so it’s about as massive as possible for a planet to be before being considered a brown dwarf. Astronomers are still debating where exactly the cutoff line between a brown dwarf and a planet should be, so looking at planets like TOI-4603b can help them decide how to classify these two different types of objects.