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Hello, my name is Sanjeev Gupta and I am a long term planner for the Mars Curiosity rover.
This is your Curiosity rover update. We've now been on Mars for almost 2 months and we have been
witnessing the amazing new vistas of the never-before-seen Gale landscape taken with our wonderful cameras.
However, much of the science team have had their eyes and the rover's eyes firmly focused on the ground.
On the drive from the Bradbury landing site to our current location
we have been analyzing three really interesting outcrops that we have called Goulbourn, Link, and Hottah.
If we look at the Hottah outcrop, we can see a distinct layer that has been tilted
and eroded and this allows us to look at the cross-section through the layer.
When we looked at the layer with our high-resolution Mastcam camera we found that it
was comprised of sand grains and small pebbles that had become cemented to form a hard layer.
Here you can see a pebble that is 3 cm in diameter; so smaller than a ping pong ball.
This suggests that this layer is an ancient gravel deposit. The surprising thing is
that when we looked at the pebbles closely, we discovered that many of them were quite well-rounded.
This is very different to the many angular clasts that litter the surface.
Here, you can see a rounded pebble from a riverbed on Earth.
On Earth rounded pebbles are a common tell tale sign of rocks that have been transported by water.
For example, in a river or a stream, as water flows over a riverbed, if the flow strength is great enough,
the pebbles are lifted up into the flow or rolled along the riverbed and they become pounded and battered
against each other and this causes them to become rounded through time. So what we think we might be seeing
here on Mars is an ancient riverbed with the pebble beds representing old stream deposits.
The size of the pebbles tells us that these rocks could not have been transported by wind, so it seems
clear they must've been transported by water. So how does a pebble deposit get to be here?
If we look more broadly in Gale Crater, we can see that there is a prominent feature that geologists call an
alluvial fan. Alluvial fans are cone-shaped deposits of gravel and sand that accumulate where streams exit
mountains. In Gale crater, there is a 10 km long fan formed at the mouth of 30 m deep canyon that is
derived from the crater rim. On the fan itself we can see evidence for multiple channels suggesting that the
streambed direction changed through time. When we look at the location of the Curiosity landing site with
respect to the alluvial fan, we see that the rover landed down stream of the fan. The rounded pebbles likely
represent long distance transport down the alluvial fan. So this is really exiting news for the science team
because this is the first time we are seeing gravel transported by water on the surface of Mars.
This has been another exhilarating week for Curiosity on Mars and for the scientist team here in Pasadena.
This has been your Curiosity rover report. Check back for more updates.
NASA Jet Propulsion Laboratory, California Institute of Technology