A couple of quick notes on the implementation:

1. The marker and buffer logic leans on LineUtility.Simplify to pick a subset of the asteroid's collider's points. (In my defence, I'd almost certainly go with Ramer-Douglas-Peucker to simplify the polygon even if it weren't available in the Unity standard library.) This requires a tolerance value, which is exposed in the inspector. Setting tolerance to 0 plots every collider and buffer point; higher numbers will produce fewer points. 10 is a pretty good value, although YMMV.
2. Generating buffer points on non-convex polygons is tricky, so I cheated. I've introduced an external dependency in the form of the Clipper library, which implements Vatti's polygon clipping algorithm. Because this seems to violate the spirit of the problem, I've also included a naïve algorithm that attempts to offset (i.e., buffer) the collider polygon by estimating the best outward-facing norm for each point, based on its neighbours. This would work pretty unexceptionably for convex (and gently concave) polygons but has difficulty handling tight convex areas (it'll produce outliers in the south-southeast part of the asteroid in particular, for example). There's a checkbox in the inspector that allows you to switch between the Clipper-driven implementation and my hand-rolled approach.