As Curiosity starts moving towards Mount Sharp again, a few more of those odd “bubble” features have been seen. The most obvious ones are oval-shaped, with raised rims, and appear to be a bit larger than some others seen previously. Like the others though, they sort of look like frothy bubbles which have “popped” and then hardened. How they formed is still a mystery which hopefully Curiosity can shed some more light on.
The one from sol 309 looks like a little circular wall with openings in places where it doesn’t touch the ground, making it appear rather fragile. There is also some light-coloured material inside it; is it the same stuff as the other light-coloured patches seen elsewhere?
As of right now there are still only lower-resolution Navcam and thumbnail Mastcam images of the one from sol 307, so some full-size Mastcam or MAHLI shots would be nice. They are an interesting feature, not seen by other rovers or landers before. The previously reported bubbles can be seen here, here, here and here.