Sunday, 30 March 2014

The Curious Layers of Mars

It has been an extremely long and hard winter this year in the north-eastern portions of North America and I find myself in need of some cheering up. Nothing is so cheery as pretty pictures of planetary surfaces. So today I am going to talk about some of the beautiful imagery that's been coming from the Curiosity rover on Mars, specifically the lovely layers of sedimentary rocks.

Many Layered Sandstones
Many layers of soft and hard sandstone rocks make these step-like structures on Mars. The Curiosity rover collected this image in Gale Crater on Feb. 25, 2014.
 To learn more about this image, go to the JPL Space Images website.
Image Credit: NASA/JPL-Caltech/MSSS

Curiosity landed in the Gale impact crater on Mars in August of 2012 and has been exploring the floor of that crater ever since. The going is slow though. The rover's average travelling speed is about 30 meters per hour. In comparison, most people can easily walk 3 kilometers (3000 m) per hour. But the rover is actually even slower than its average travelling speed. First, it's goal is to explore Mars, so it makes many stops to gather science data. Second, it needs to pick its path carefully to avoid obstacles. So it's not always following the straightest route. In the early days of the mission, sharp rocks were puncturing the rover's aluminum wheels, but now careful route planning has helped to minimize such damage. But that care takes time. In the end, Curiosity has moved only about 4 kilometers from its landing site in the first 561 martian days of operations (a martian day is about 40 minutes longer than an Earth day).

Topography of Gale Crater
The Curiosity rover landed on the floor of Gale impact crater on Mars, just north of Mount Sharp in the centre of the crater. The landing location is highlighted here by the black oval.
To learn more about this image, go to the NASA mission page:
Image Credit: NASA/JPL-Caltech

The type of terrain Curiosity has been passing through has changed in those 4 kilometers, though. The rover's original landing site was relatively flat with only a scattering of small pebbles on the ground. This is actually a good thing for a landing site, since you wouldn't want your rover to land on a cliff or large boulder.

Landing Site Panorama
The Bradbury Landing site (named after Martian Chronicles author Ray Bradbury) is very flat and shows no evidence of layering. The mountain in the distance at the top centre of this image is Mount Sharp.
To learn more about this image, go to the JPL Space Images website.
Image Credit: NASA/JPL-Caltech/MSSS

Ever since it landed, Curiosity has been steadily making its way to the large mountain in the centre of Gale crater, called Mount Sharp. The base of Mount Sharp, which is about 20 kilometers south from the landing site, is the rover's ultimate destination. This region is of great interest to scientists because it contains a very thick exposure of layered rocks, which may reveal several billion years worth of clues about this region's history. 

Landing to Present Traverse
Ever since arriving at Bradbury Landing, Curiosity has been making its way south to Mount Sharp, stopping at a number of planned waypoints along the way. This image shows exactly where Curiosity has traversed, up to day 561 (March 5, 2014) of the mission. Murray Buttes is thought to be a good entry point to the base of Mount Sharp.
To learn more about this annotated image, go to JPL Curiosity Rover Multimedia website.
Image Credit: NASA/JPL-Caltech/Univ. of Arizona

But, Curiosity did not have to go all the way to Mount Sharp to find layered rocks. Those it found relatively soon after landing. More recently, on Feb. 25, 2014, Curiosity arrived at a location where many different types of layered rocks can be seen in one place (see the image at the top of this post).

The layered rocks here are thought to be sandstones. This is a type of rock that is literally made up of sand grains glued together by some kind of cement. If the cement is made up of clay materials, the sandstone is relatively soft and can be easily eroded by wind and water. If the cement is made up of hard quartz minerals, the sandstone is very durable and hard to erode. When layers of hard and soft sandstone occur together, they make step-like structures, where the hard sandstone forms caps protruding over the soft sandstone that is eroding away.

Scientists are not clear on why there would be so many different layers of soft and hard sandstone in this one place, or how they formed. But, they are hoping for some answers soon. About 400 meters away is the planned Kimberly waypoint. This area was identified as a point of interest from satellite images, because four different-looking rock types seem to intersect there. And it is expected that layered sandstones will be found at the Kimberly waypoint. The Curiosity rover will stop there for a time to conduct scientific investigations.