At https://phys.org/print412490580.html … an interesting link after Bob Johnson's talk at the SIS Spring Meeting on 29th April. The orbits of the planets are affected by two uniformitarian acceptable processes – one developed by Einstein, and the other, by Newtonian theory of gravity. In the latter an orbit becomes narrower over time, more and more elliptical, moving the object closer to the Sun at it's furthest point. The other concerns the periodic shift of the orbit of Mercury which is part of general relativity. Then we have the pull of Jupiter – which affects smaller objects such as comets, changing their orbits.
Craters around the world on the RH and variations in the orbit of Mercury on the LH.
Orbital evolution potentially can occur at any moment in time -especially when it comes to comets and asteroids. Having noted all that the piece then looks at what it might mean as far as impact strikes on Earth are concerned, regarding small solar bodies. Jupiter's periodic effects can lead to a close approach of a fairly big lump of rock and gases, a scenario not always appreciated. The Earth's surface is pockmarked with craters, they say, and therefore collisions from space have happened in the past – and may do again. See Monthly Notices of the Royal Astronomical Society (2017).