Historian and scientific researcher Kenneth J. Dillon discusses his theory The Outer Solar System Origin of the Terrestrial Planets (OSSO). OSSO explains how Mercury, Earth, the Moon, and Mars originated outside the orbit of Saturn, then were pulled inward by Jupiter’s gravity. Tidal friction heated them to incandescence, then they tidally locked to Jupiter and were separated, moving as comets into their present orbits. See also https://www.scientiapress.com/outer-solar-system-origin.