When Captain Cook sailed into Botany Bay in 1770, we did not know how many planets were in our solar system. We only knew about Mercury, Venus, Earth, Mars, Jupiter and Saturn.
Based on the orbits of these planets, 18th century European astronomers invented what is now called the Titius-Bode relation. It’s a simple empirical relation that describes the relative distances between the planets and the sun. It predicted the orbit of another planet beyond Saturn and another planet in the gap between Mars and Jupiter.