How to loop animations If the orbital period of earth is 1, the period of Mercury is 0.241.

In the Timeline, I scaled Mercury to said period by pressing S, .241.

How can I get Mercury to continue it's motion rather than waiting for the animation to restart?
You can select the object, in the Dopesheet select its keyframes (to only see this object's keyframes, use the Only Include Channels Relating To Selected Objects option, small arrow icon button) and press ShiftE > Linear Extrapolation, and the object should continue its rotation infinitely.