Sun-earth-moon system may not be stable
The application of zero-velocity surfaces (a mathematical technique) to the sunearth-moon, three-body system indicates that the eccentricity of the earth's orbit renders the system unstable. The conclusion is that the moon may one day escape the earth and become a planet and, turning the situation around, that the origin of the moon by capture is a strong possibility.
(Szebehely, V., and McKenzie, R.; "Stability of the Sun-Earth-Moon System," Astronomical Journal, 82:303, 1977.)
Comment. This paper is typical of several recent ones in celestial mechanics that throw doubt on long-held dogmas about the long-term stability of the solar system. For more on this subject, consult ABB1 in our Catalog: The Sun and Solar System Debris. To order this book, visit: here.