I feel like these are the barnacles we are looking for as someone else said earlier:
View attachment 93764
Also, the thrusters pointing down means the world is equal or higher than 1g, not necessarily exacly 1. I don't think this is mandatory for the random spawn ones though.
BTW, if these are the barnacles (I strongly believe so) they seem to be at different stages of maturity so if they can spawn separately, they may or may not be emitting light.
I would consider that picture as more like a mining outpost for the "others" than maturing UA (this is how i guess we will get the meta alloys by killing the living mining drill -my theory- ) . We could also be looking for a launching site to send them into space. any how it needs to be very big for us to see it from 10to 15 km (in order to cover a lot of ground)and I hope I will once found appear as a POI on your surface map.