Can moons have their own natural satellites? This issue was widely discussed last year after the publication of the draft study. It indicated that theoretically moons could rotate around moons. On the Internet, controversy began about how best to name a new type of object. However, researchers were more interested in the possible physical parameters of celestial bodies capable of stably rotating around the moons.
The planets revolve around the stars, and satellites move around the planets. Then it is logical to assume that moons can move around the satellites. Is it so? Recent calculations have shown that only large satellites in wide orbits from their home planets can have smaller moons. Tidal forces from the planet and moon will destabilize the orbit of the moon.
In this case, only 4 satellites in the solar system could theoretically exist with their own moons. These are Callisto (satellite of Jupiter), Titan and Iapet (Saturn), and also our Moon. All of them are suitable, but so far not a single moon has been found. Scientists add that more in-depth calculations are needed to eliminate possible sources of gravitational instability, such as inhomogeneous mass concentration in the crust of our Moon. The satellites near Saturn and Jupiter are believed to have formed from a disk of gas and dust around the giants in the later stages of formation. However, it is believed that our moon appeared after a giant collision of the planet with a body of Martian size. The absence of a sub-moon will help to understand the various forces that formed the observed satellites.
In addition, it will allow to better understand how the planets develop in other star systems. For example, they recently discovered a possible exoluna around Kepler 1625b - a planet with the size of Jupiter. The satellite has the necessary distance and mass to have its own moon. But because of the inclination of the orbit, it will be difficult to save the object.
The findings of the researchers suggest that the moon is better to look for in systems with massive stars. The fact is that the red dwarfs have close habitats where there are too strong tidal forces, and the moon has no stability.
