Gloopy fluid makes bigger ripples

By understanding how ripples form in sand, geologists can gain a valuable insight into past conditions - both on Earth and on Mars

Ripples in the sand are a beauty to behold. Sometimes their sinuous curves can be spied beneath a tinkling stream, and other times you feel them under your feet as the currents in the sea create ridges and hollows in the sand.

But what controls the size and shape of a ripple? Is it the size of the grains, the depth of the water, or perhaps the strength of the flow? For geologists the question matters because they use fossilised ripples to try to better understand past environments or interpret conditions on other planets.