Gas giants have some of the characteristics of brown dwarfs. Like the Sun, Jupiter and Saturn are both made primarily of hydrogen and helium.

Why is Jupiter not considered a brown dwarf?

What about substellar brown dwarfs? Our largest planet still doesn't come close to these “almost stars.” Astronomers define brown dwarfs as bodies with at least 13 times Jupiter's mass. ... So, while Jupiter is a planetary giant, its mass falls far short of the mark for considering it a failed star.

Can Jupiter become a brown dwarf?

Jupiter, while more massive than any other planet in our solar system, is still far too underweight to fuse hydrogen into helium. The planet would need to weigh 13 times its current mass to become a brown dwarf, and about 83 to 85 times its mass to become a low-mass star.