Observations and Discoveries in the Solar System

Abstract

In 1772, the Berlin astronomer E. Bode (1744–1826) made public the empirical law of planetary distances discovered in 1766 by I. Titius, an astronomer at Wittenberg, which is now known as the Titius–Bode law. Titius had noticed that if we indicate with the number 4 the average distance separating Mercury from the Sun, the distances similar to Venus, Earth, Mars, Jupiter and Saturn can be expressed by the Figures 4 + 3, 4 + 6, 4 + 12, 4 + 48, 4 + 96 and that if this sequence of numbers is to be continuous, it lacks the Figure 4 + 24. The progression has no real scientific foundation and is not derived from any of the principles of celestial mechanics, but this did not matter, and even among those who understood the weakness of the hypothesis spread the idea that between Mars and Jupiter, at a distance expressed in the harmonic progression from number 4 + 24, there must be a celestial body that was still unknown. When Herschel discovered Uranus in 1781, it was quickly pointed out that the distance of this new planet from the Sun was expressed well enough by the value 4 + 192, which is framed perfectly in the progression of Titius. Therefore, there should also exist the planet corresponding to the value 24 of the progression—a planet located between the orbits of Mars and Jupiter—certainly weak and probably only visible through a telescope.