The 5 inner planets of the K2-138 system are playing an enchanting melody. For every 3 orbits each planet makes, the next planet outward completes 2 orbits. This means that for each pair of neighboring planets, the outer planet's period is always 1.5 times the period of the inner planet.

This is the same pattern found between Neptune and Pluto.

This pattern can be associated with the musical jump called a perfect fifth, the same two notes that start 'Twinkle, twinkle, little star'.