Since there is no perspective available, it could be much smaller than that you are imagining. When you look at the other picture, showing the ice field, there are a few big rocks around, but notice they don't identify any of those racks as being the space rock. 🙂
But I wholeheartedly agree with your sentiment. 🙂
A shot put is 16 pounds, so if it’s iron, it’s at least as big as that. If it’s stony, then maybe volleyball sized?