Atom's structure

Nagaoka’s Saturnian model, definition and characteristics

Nagaoka’s Saturnian model, definition and characteristics

In 1904 Hantaro Nagaoka developed an atomic model that complemented Thomson's atomic model. The Nagaoka model is also known as the Saturnian atomic model or planetary model.

This atomic model is a hypothetical model of the atomic structure, unlike Thomson's raisin pudding model. In this model, the existence of the atomic nucleus was postulated for the first time.

What is the Nagaoka atomic model?

At the beginning of the 20th-century, physicists had only just begun to understand the structure of the atom. It was after studies of Dalton’s atomic model and Thomson’s atomic model.  The discovery of the electron showed up the existence of negative charges in the atom. It implied that positive charges also existed.

Nagaoka based his theory on the fact that opposite electric charges were massive, impenetrable spheres with a positive electric charge. This sphere was the atomic nucleus and was surrounded by several negatively charged electrons orbiting around it. Nagaoka described these orbits as circular orbits, equivalent to Saturn and its rings.

Nagaoka explained atomic stability according to his model with an analogy to the stability of Saturn's rings. James Clerk Maxwell had recently published a study on this model and made two predictions:

  • the existence of a very massive nucleus, in analogy with the disproportion between the mass of Saturn and that of the ring.

  • Electrons revolve around the nucleus bound by electrostatic force, like the particles of the ring revolving around Saturn by gravitational force.

How did the Nagaoka model influence Rutherford's atomic model?

Both predictions were sufficiently confirmed by Ernest Rutherford. Rutherford mentioned Nagaoka’s Saturnian model in the 1911 article reporting the discovery of the nucleus.

However, Rutherford's atomic model revealed just how wrong the Saturn model was. In reality, the core was much smaller than Nagaoka had assumed. Furthermore, a ring with an electric charge would have been unstable to oscillations in a direction orthogonal to the plane of rotation of the ring.

Rutherford's discoveries would serve as the basis for studies to develop Niels Bohr's atomic model and later Sommerfeld's atomic model.

Nagaoka’s Saturnian model was unable to predict some phenomena. Consequently, Nagaoka abandoned his model in 1908.

Who was Hantaro Nagaoka?

Nagaoka Hantarō (August 15, 1865 - December 11, 1950) was the most prominent Japanese physicist during the late Meiji period. He was one of the founders of the Japanese physicists who began the Meiji period, the founder of the scientific school. Author of various works on electricity and magnetism, atomic physics, and spectroscopy.

He was born in Ōmura, Nagasaki Prefecture ad trained at the University of Tokyo. After graduating in 1887, he collaborated with British physicist Cargill Gilston Knott on studies of magnetism. In 1893 he moved to Europe, where he completed his training at Berlin, Munich, and Vienna.

In 1900 he attended the First International Congress of Physics in Paris. In this congress, he heard Marie Curie's lecture on radioactivity, an event that increased Nagaoka's interest in atomic physics.

Nagaoka Main Works

Hantaro Nagaoka rejected Thomson's model because opposite electric charges are impenetrable and proposed the alternative atomic model explained above. However, he abandoned it in 1908.

After abandoning his atomic model, Nagaoka took up spectroscopy and other fields. In 1909, he published a work on the inductance of solenoids.

In March 1924, he described experiments where he claimed to have obtained one milligram of gold and some platinum. The discovery was made by subjecting mercury to an electric field of 15 × 10 ^ 6 V / m for a few hours. He repeated the experiment later with conflicting results.

In 1929, Nagaoka detected radio disturbances produced by meteors. The Japanese physicist hypothesized that it would be possible to establish communication between two stations on the ground. To do this, it used, as a radio link, the ionized trail left by the meteoroid when it enters the atmosphere.

Publication Date: August 15, 2021
Last Revision: August 15, 2021