Indeed they did. They knew of all the planets including knowing the colors of Neptune and Uranus. It was chronicled many times in sculpture and in cuneiform. They also knew of precession and the 12 houses of the zodiac.
The existence of Pluto wasn’t known to the Sumerians. They were similarly ignorant of Neptune and Uranus. If it were chronicled many times in sculpture and in cuneiform, it would have been remarked on by actual scholars of cuneiform and Sumerian, rather than by Zecharia Sitchin. The fact is, it doesn’t occur even once.