Complex sentence: This feature was "revolutionary" because it was inconsistent with the expectation that an electron could be bound to an atom's nucleus by any amount of energy, just as a planet can be bound to a star by any energy.
Split into simpler sentences: This feature was "revolutionary" because it was inconsistent with the expectation that an electron could be bound to an atom's nucleus by any amount of energy. A planet can be bound to a star by any energy.