Can the Moon have its own moon? ⚡ экспресс
Within a constant geometric lag model for tidal dissipation, the Euler-Lagrange equations were solved numerically, and the parameter space of star–planet–moon–submoon systems with submoons massive enough for life was explored. Earth could hold onto asteroid-mass submoons (~10^15 kg), while a submoon at the upper limit (~4.6·10^17 kg) would push the Moon ~30% farther from its current orbit. For the warm Jupiter Kepler-1625b: a submoon with ~10% of the moon's mass is stable if the moon is at a distance of 67 R_p (instead of 40 R_p). Giant submoons (1.8 M⊕) are stable with a wide moon orbit (>100 R_p). At a mass of 0.5 M⊕ (a condition for an atmosphere and tectonics), the number of stable configurations drops. A stability minimum is found at ~0.1 M⊕, explained by the balance of tidal forces and the Roche limit. If the formation of submoons in such systems tends toward intermediate masses, habitable submoons may be rare.
The Moon can have its own tiny moon — like a nesting doll, but in space. The outer doll is a planet, the middle one is a moon, the inner one is a small moon-satellite, or submoon. Ньютон showed that all bodies attract each other, and gravity holds them together. But gravity is not uniform: on the near side of the satellite it's stronger than on the far side. This difference creates tidal forces that squeeze and stretch the object, like clay. If a submoon gets too close to the main moon, it gets torn apart — possibly just like the dusty ring around Saturn's moon Rhea was torn apart. искривление пространства-времени explains this as a deformation of space itself.
Calculations show: Earth could host an asteroid-sized submoon. If it were bigger, the Moon would move 30% farther away from us. For экзопланеты Kepler-1625b — a warm gas giant — submoons could be as large as Earth. For life to arise on such a moon, жидкая вода, an atmosphere, and plate tectonics are needed, meaning the mass should be about half of Earth's. But precisely at that 'half' mass the orbit becomes unstable — a paradox that might make habitable submoons extremely rare.
🎯 Saturn's moon Rhea may have once had a dusty ring — almost submoons.