John Bridges: Mars Science Laboratory Blog
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We have been analysing the Windjana drill tailings for over 2 months now and have just dumped the drill tailings.
The long and repeat analyses by SAM and CheMin allowed us to look at the effects of degassing of samples over time (e.g. the noble gas argon, used in K-Ar dating) and to get the best XRD analyses. Exposing the drilled powder samples to the X-ray source over several occasions allows us to track any potential changes e.g. in hydration state of the tailings and to get better 'counting statitics' from which mineral abundances are determined. For that we fit the position and shape of the peaks to standard spectra here on Earth using what is called the Rietveld Method.
Recently MastCam and ChemCam imaging revealed 2 iron meteorites along our traverse. These are the first found by Curiosity, though the 2 MER, Spirit and Opportunity also identified iron meteorites.
The Curiosity ones: called Lebanon and Littleton were identified by their high reflectivity ('specular') compared to the other rocks, native to Gale Crater. They are < 1 m across.
The freshness of the meteorite surfaces suggests that they have not been exposed to the water and salts that the mudstones and other sedimentary rocks experienced.
An interesting puzzle is that we have only ever seen iron meteorites on Mars. Stony meteorites are by far the the most common sort on Earth and were also identified on the lunar surface by Apollo 17. Was there a recent break up of an iron meteorite parent body which led to a shower of meteorites on Mars or is it that the shiny surface enables us to identify iron metorites, but stony meteorites are more difficult?
The image below shows a ChemCam RMI image superimposed on a Mastcam image. The pitted surface shows regmaglypts, which are caused by the passage of a meteorite through an atmosphere. The action of sand carried by the wind in reecnt times on the surface of Mars may have enhanced these features.
In addition to driving towards the Murray Buttes gap in the dunes, and our path onto Mt. Sharp, we stop sometimes to do contact science. The image gives an example of what this entails. We have to get the APXS detector head as close as possible to a target of interest (in this case one of the 'float' rocks scattered on the surface) so that the intensity of the X-rays given off by the sample after bombardment by the alpha paticles from APXS does not diminish. In this image you can see how the robotic arm turret head has been rotated to bring the APXS clsoe to the target rock.
Here is a new classic image from Mars: a selfie from Kimberley. You can see the dark drill hole and the practice drill hole beside it. Curiosity itself is looking a bit dusty after a year's work on Mars. Images like this always remind me how big the rover is in relation to many of the outcrops we are looking at. Keeping track of the scale of rocks is always important.
As a result of all our driving - a total of about 8 km - we have just passed across our the line of our original 20 km diameter landing ellipse.
Meanwhile at Terra Meridiani - site of the solar powered MER rover Opportunity, which landed in January 2004, has named a site at Endeavour Crater, Pillinger Point. This is in honour of Colin Pillinger - the lead scientist behind the Beagle2 mission and a man who did much to push forward planetary science in the UK and Europe.