Complex sentence: The Uranian satellite system is the least massive among those of the giant planets; indeed, the combined mass of the five major satellites is less than half that of Triton (the seventh-largest moon in the Solar System) alone.
Split into simpler sentences: The Uranian satellite system is the least massive among those of the giant planets. Indeed, the combined mass of the five major satellites is less than half that of Triton (the seventh-largest moon in the Solar System) alone.