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SYFY WIRE Bad Astronomy

I Didn’t Even Know Mars Had a Southwest

By Phil Plait

Since 2012, the Curiosity rover has been tooling around the surface of Mars. It landed in Gale Crater, an ancient impact site nearly 100 kilometers across, and its destination has been the base of Mt. Sharp, the informal name of Aeolis Mons, the crater’s central mountain that towers 5.5 kilometers above the ground.

One of Curiosity’s science goals is to look for signs where conditions for life may have been good a billion or more years ago. This means finding things like clays and other minerals that form in water.

Or, say, like sandstone.

Curiosity is currently in a spot on lower Mount Sharp called the Murray formations, named after planetary scientist Bruce Murray. This area used to be a dune field an eon or two ago, but then filled with water and formed a lake. That water is long gone, but it profoundly affected the sand it soaked into. It deposited sediments in between the sand grains, cementing them together to form sandstone. When the water went away, winds began to erode the sandstone, and after enough time, carved the Murray Buttes.

Aren’t these beautiful? They look like they could’ve been photographed in Utah or New Mexico, but this is Mars! Curiosity took them on Sept. 8, just a few days ago.

The layering you see is from when this was still a dune field. The wind would blow the sand off the dunes, sorting and layering it. Some of the layers were on the dune slopes, and were tilted with respect to the other layers. Once mineralized it formed angled layers called “cross bedding,” and created incredible scenes like this:

Seriously. What a view! And different regions eroded at different rates, giving a profile of sharp, jagged edges against the butterscotch Martian sky.

The reddish color is from iron oxide—rust—in the dust of Mars, and in fact is the same reason there’s so much red sandstone in the American southwest. Long ago there were the ancestral Rocky Mountains, before the present ones, which were rich in iron. They eroded over millions of years, and the rusty remains formed a sea bed. That inland sea went away, and now we have red sandstone everywhere (it’s a very common building material in Colorado).

All that happened here on Earth from about 300 million to 50 million years ago. It’s possible the sandstone you see in these images on Mars was already old by then.

I love this mission of looking for life on Mars. When I see pictures like these I am strongly reminded of how Earth-like Mars can be, and how clement it once was. When the Earth was still too hot after its formation to support life, Mars was cool enough to get a head start. We know life here started up relatively easily, so why not Mars? It was doomed, since the planet’s lack of a magnetic field allowed the Sun to strip away most of its atmosphere and its water.

But it’s possible Mars once had life, and we could find the remains of it, or some other indication it once existed. I hope we actually do find it, because the implications of that would be profound.

But I also love that we, as a species, have chosen to make this search at all. I think it says something important and special about us that we do.

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