The 40-year mystery of the Martian ice cap solved

Op Yahoo News.

PARIS (AFP) – Astronomers on Wednesday said they could explain a nearly four-decade-old enigma surrounding rugged troughs and a chasm in the northern ice cap of Mars that could comfortably house the Grand Canyon.
The Red Planet's northern cap measures around 1,000 kilometres (600 miles) across, with layers of ice and dust stacked up to three kms (two miles) deep.
It also has two remarkable features that have bedevilled scientists ever since they were exposed in detail by US probes almost 40 years ago.
One is the Chasma Boreale, a depression 500 kilometers (310 miles) long, up to 100 kms (60 miles) wide and two kms (1.2 miles) deep.
Many experts have surmised that the Chasma Boreale was created by volcanic action that melted the bottom of the ice sheet, triggering a flood that gouged out this mighty gash in Mars' surface.
Another mystery is a spiral of troughs that radiate out through the polar cap, rather like a pinwheel.
Its strange symmetry caused some experts to wonder whether the troughs were formed by a centrifugal force caused by the spinning of the planet.
The Chasma Boreale, far from being born in a catastrophic event, occurred through an aeons-long process, the scientists believe.
Wind eroded a gap in a base layer of soft sand and ice, rather like a river on Earth cuts its way through a valley, relentlessly exploiting the softest rock.
Further deposits of ice and dust then accumulated on either side of the gap, creating the slopes of the canyon.
As for the spiral troughs, the distinctive swirl was created by the Coriolis force, a well-known phenomenon on Earth in which winds are deflected by the planet's spin.

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