What is the difference between a brown dwarf and a planet?

Brown dwarfs and planets share many similarities but there are some key differences between them. Brown dwarfs are sometimes referred to as 'failed stars' as they are too small to sustain nuclear fusion in their cores, but they are larger and more massive than planets. Planets, on the other hand, are generally smaller and less massive than brown dwarfs.

Another key difference between brown dwarfs and planets is their formation process. Brown dwarfs form in much the same way as stars, through the gravitational collapse of gas and dust in a molecular cloud. Planets, however, form through the accretion of material from a protoplanetary disk around a young star.

One of the most important distinctions between brown dwarfs and planets is their internal structure. Brown dwarfs have a more star-like structure, with a dense core of metal and hydrogen surrounded by layers of molecular hydrogen and helium. Planets, on the other hand, have a more differentiated structure, with a dense core of rock and metal surrounded by layers of ice and gas.

Finally, brown dwarfs and planets have different temperatures and luminosities. Brown dwarfs are hotter and brighter than planets, but cooler and dimmer than stars. Planets, meanwhile, are much cooler and less luminous than brown dwarfs, and are primarily heated by the radiation they receive from their host star.