The north pole of Mars is topped with a bizarrely-shaped icecap, riven by deep chasms larger than the Grand Canyon that create a whirling spiral shape. At last scientists have discovered what ancient force created this strange geological feature.
For the past 40 years, ever since the shape of the cap was revealed by satellites, scientists have debated the origins of the spiral chasms. They've suggested everything from volcanic eruptions to the motion of the planet as it spins. But it turns out that one man knew the answer all along, though nobody took him seriously when he first suggested it in the early 1980s. Now a paper published today in Nature, based on measurements taken by the Shallow Radar device, vindicates this prescient scientist's view. Below, you can see a reconstruction of the inside of one of the chasms.
University of Virgina astronomer Alan Howard suggested erosion from the wind as an explanation. Isaac Smith, lead author on the Nature paper, says:
He only had Viking images with relatively low resolution. Many people proposed other hypotheses suggesting he was wrong. But when you look at a hypothetical cross section from his paper, it looks almost exactly like what we see in the radar data.
The Italian Space Agency provided NASA with the Shallow Radar device, which plumbed the layers of the ancient icecap, essentially peeling back millions of years worth of geological history to determine that winds, shaped by planetary motion, had gradually carved a deep spiral chasm into the planet's north pole.
In a release about the paper, the scientists explain how the wind did this:
Why are the troughs spiral shaped? First, katabatic winds are caused by relatively cold, dense air that rolls down from the poles and out over the ice cap. Second, as they blow down, they are deflected by the Coriolis force, which is caused by the planet's spinning in space. On Earth, this is what causes hurricanes to spin opposite directions in opposite hemispheres. This force twists the winds-and the troughs they create-into spiral shapes.