After more than three years on the Martian surface, the car-sized Curiosity Mars rover is giving us a close-up glimpse of terrain unlike anything we've seen before: tall, rippled sand dunes like this one:

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Satellites orbiting Mars, like the Mars Reconnaissance Orbiter have snapped photos of sand dunes like these before:

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But we've never seen these alien mounds up close like this:

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And NASA scientists are incredibly excited because it's the first time anyone has had the chance to study active sand dunes on another planet, beyond Earth.

One of the first things they want to explore is the "grain size and morphology of different parts of the slipface," Lauren Edgar, a member of the Curiosity team and a USGS Astrogeology Science Center research geologist, wrote in a mission update.

The ripples on these dunes change over time due to Martian winds and miniature avalanches. Notice in the picture below the breaks in the ripple pattern near the top:

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These breaks happen after Martian winds deposit sand on the slope, where it gradually accumulates. Eventually, so much sand builds up that the sand underneath can't sustain the weight of the sand on top, and a mini-avalanche occurs.

On Earth, this sort of thing usually happens on wind-protected slopes, leading NASA scientists to conclude the side of this dune, called Namib Dune, is also shielded from the wind.

For comparison, the wind-facing side of another nearby dune reveals a very different sand pattern:

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This mound is between 13 to 17 feet tall and is just one of many sand dunes located in the Bagnold Dunes field situated along the northwestern flank of the base of Mount Sharp, which forms Gale Crater's central peak.

Gale Crater is initially where Curiosity first touched down back in 2012. Here's a map of where Curiosity landed in the upper right, and where it has gone over the last 1196 sols, or Martian days:

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And here's a better view of the environment, with Namib Dune on the right:

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Mount Sharp is a 3.4-mile-high mountain that NASA's Curiosity team has been dreaming of exploring for a long time. They first snapped a photo of Mt. Sharp with Curiosity's Hazard-Avoidance camera in 2012 — that's Mt. Sharp in the distance:

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Though NASA scientists haven't seen sand avalanches or ripple movement yet, Edgar is hopeful:

"We’ll be in the same location for a little while, so hopefully we’ll have the chance to observe some sand movement!"

In the mean time, we can sit back and enjoy some amazing photos, like this breathtaking panoramic view of Curiosity's rover deck, Namib Dune in the middle, and Mount Sharp's peak in the background:

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