* Lack of Fusion: Stars generate light and heat through nuclear fusion, where hydrogen atoms fuse into helium. Jupiter is simply too small and lacks the immense gravitational pressure needed to initiate this process.

* Composition: While Jupiter is mostly made of hydrogen and helium, like stars, it also has a significant amount of heavier elements. This is unlike stars, which are almost entirely hydrogen and helium.

* Temperature: Jupiter's internal heat is generated by gravitational pressure and leftover heat from its formation, not by nuclear fusion. This means it's much cooler than a star.

* Luminosity: Jupiter reflects sunlight, making it appear bright. It doesn't produce its own light like a star.

* Mass: Jupiter is significantly less massive than the smallest stars. It would need to be about 80 times more massive to have the necessary gravitational force to start fusing hydrogen.

In short, Jupiter doesn't have the key ingredients and conditions to be a star. It's a giant planet, a massive ball of gas, but not a self-luminous, energy-producing object like a star.