[prewett]

Given the slower speeds in the outer solar system, especially since they will be rotating in the same direction, so the relative speed will be less, I would imagine that contact binaries would be fairly common. And since they are primarily made of ices, the actual contact event should melt the ice, which will then re-solidify since the impact speed is so little.

I don't know if this is how it actually happens, but it gives a mechanism for this being fairly common. The only information I could find was a short wikipedia article:

https://en.wikipedia.org/wiki/Contact_binary_(small_Solar_Sy...