With the terrain selected, click on the E for edit button. Find the Editing Tools pallete, click-and-drag to the right, on the button next to Round Edges. This will give a smoothed-out  round base to your terrain, which will fit easier on a sphere.

Be sure to scale the resulting planetary sphere and it's terrains so they are in proportion, though. As you show, the mountain might be suitable for an asteroid (or maybe Mons Olympus, but not an Earth-like planet.

RosemaryR
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"This...this is magnificent!"
"Oh, yeah. Ooooo. Aaaaah. That's how it starts.
Then, later, there's ...running. And....screaming."