To try to get some answers, a new study analysed 30 of the strange glacier mice on the Root Glacier in Alaska, using bracelets of beads to measure the movements of the balls across a period of four years.

"By coming back year after year, we could figure out that these individual moss balls were living at least, you know, five, six years and potentially much, much longer.".

"We could not explain the direction of moss ball movement by considering the physical surface of the glacier (i.e., the downslope direction), the intensity of glacier ice ablation, and patterns of solar radiation," conclude the researchers

"Thus, it appears a still unknown external force influences glacier moss ball movement on the Root Glacier."