GIANT steps etched into the landscape of Mars just north of its equator lay bare the flip-flopping of the planet鈥檚 climate.
A team led by Kevin Lewis of the California Institute of Technology in Pasadena used the 3D viewer of the HiRISE camera on board the Mars Reconnaissance Orbiter to image the landscape at four locations in the region of Arabia Terra. At each site, they found giant steps of sedimentary rock, all roughly the same height and bundled into groups of 10 (see photo).
Advertisement
The fact that layers of softer and harder sediment graduate into each other alternately to form the steps in the image suggests that some cyclic climate change was at work when the rocks formed.
One possible explanation is a wobble in Mars鈥檚 axis that tilts it back and forth over a cycle of 120,000 years. This tilt affects the planet鈥檚 climate, changing patterns of snowfall and atmospheric pressure, which could easily have influenced the rock鈥檚 hardness. What鈥檚 more, the wobble strengthens and weakens over a sequence of 10 to 20 climate cycles, which might explain the bundling of the steps (Science, vol 322, p 1532).
Discovering more such deposits and comparing their patterns could allow researchers to build up a detailed time line of the Martian climate. Though the age of the sediments is unclear, they probably formed in the warmer, wetter distant past, says Lewis. 鈥淚n all likelihood, they are telling us about the ancient climate of Mars, billions of years ago.鈥�