Why is Jupiter classified differently from the Sun, despite sometimes being called a 'failed star'?

Answer

It cannot fuse regular hydrogen.

While very large planets like Jupiter might theoretically fuse deuterium if slightly more massive, they do not possess the required mass to initiate and sustain the fusion of regular hydrogen, which is the benchmark for a true star.

Why is Jupiter classified differently from the Sun, despite sometimes being called a 'failed star'?
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