I’ve often wondered why Mercury doesn’t “rule” or govern all the Air signs – Gemini, Aquarius and Libra. The Air element is thought to be the most mentally related of the four astrological elements: Earth, Water, Fire and Air.
In an obtuse version of astrological rulerships, Saturn would rule Earth signs: Taurus, Virgo, Capricorn. Fire signs – Aries, Leo, Sagittarius – would be ruled by Mars.