Complex sentence: The mass of the Earth is known in terms of solar masses to ten significant figures: the same mass, in terms of kilograms or other Earth-based units, is only known to five significant figures, which is a factor of 100,000 less precise.
Split into simpler sentences: The mass of the Earth is known in terms of solar masses to ten significant figures. The same mass, in terms of kilograms or other Earth-based units, is only known to five significant figures, which is a factor of 100,000 less precise.