|Jupiter, a failed star? Not exactly.|
Since Jupiter is composed primarily of hydrogen and helium gas, yet doesn't have a high enough core temperature to fuse hydrogen, it is often called a "failed star". This is a bit misleading. A star needs to be larger than 8% the mass of the Sun for fusion to begin. Jupiter has a mass that is 0.1% that of the Sun's. In other words, Jupiter needs to be 80 times more massive to be a star. That's a very large difference. Jupiter is not even close to being a star. Referring to it as a "failed star" implies that it has a mass that is somewhat close to the minimum mass needed to be a star. I could understand calling Jupiter a "failed star" if it only needs 2 times its mass or 5 times its mass, but 80 times its mass? That's a bit of a stretch.
To conclude, in my book, it's not correct to refer to Jupiter as a "failed star". Its mass is no where near close enough to make it a star. It's a planet orbiting our star, the Sun. Nothing more.