What are these mysterious Vietnamese 'space balls'? Country's defence officials are baffled by metal spheres that have fallen from the sky

What are these mysterious Vietnamese 'space balls'? Country's defence officials are baffled by metal spheres that have fallen from the sky  Residents in Tuyen Quang province in northern Vietnam had a lucky escape after the smallest object, weighing just 250 grams struck the roof of their house near the Chinese border.