Complex sentence: Methuselah is currently one of four planets to have been given a mythological name (just like in the Solar system), although "Methuselah" is not as widely in use as the other three, the other planets being Bellerophon, Osiris, and Ymir.
Split into simpler sentences: Methuselah is currently one of four planets to have been given a mythological name (just like in the Solar system). Though "Methuselah" is not as widely in use as the other three, the other planets being Bellerophon, Osiris, and Ymir.