So it’s been a while since my last post as the university
has been pretty quiet over the summer and it’s been a good time to get my head
down and crack on with some serious sciencing without the disruption thousands
of undergraduates bring. However, after seeing this morning that the Curiosity
Rover had been doing some sedimentology on Mars,, I couldn’t help but
get a little bit overexcited. Doing geology in space must be every lithophile’s
(see one of my previous posts) dream job and so here’s a post of my ramblings
and ill-informed opinions on Curiosity and space geology and why it’s the best
thing ever (and also why I hate it).
This morning’s news report on Martian conglomerates (here, and here) is some serious proof that a significant amount of flowing water
must have been present at some point on the surface of Mars. Very poorly sorted (i.e. those with a wide array of particle sizes) conglomerates
with sub-angular to well-rounded clasts, as can be clearly seen in the photos, can only be formed by deposition from (relatively) fast flowing water. Wind
transport, which does occur due to the high Martian winds (see here) and also creates
well rounded clasts, generally creates a well sorted deposit such as an aeolian
sandstone as smaller particles are winnowed away and larger pebbles don’t roll
so far. A poorly sorted deposit could
have been formed by some sort of terrestrial gravity flow, a slump or a slide, however,
this would produce a breccia with highly angular clasts as these terrestrial
flows do not travel a great enough distance for transportation processes to
erode the particles enough.
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| Curiosity's photo shows Martian conglomerates look just like Earth ones |
The calculation that "From the size of gravels it
carried, we can interpret the water was moving about 3 feet per second, with a
depth somewhere between ankle and hip deep," [Curiosity science
co-investigator William Dietrich of the University of California, Berkeley] put
me straight back to undergraduate sedimentology lectures and the Hjulstrom
Curve.
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| Hjustrom Curve |
This graph (see above image) is a well-used tool by sedimentologists studying
fluvial transport processes in Earth systems to allow the back-calculation of
the velocity of water flow that deposited the sediment by showing what size
material will be entrained, transported and deposited by different velocities
of flow. From both the description of this shallow, fast moving stream and
looking at the deposits I’m put in mind of braided river channels in upland
areas arid areas like this (but without the shrubs):
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| Braided river system (image from http://faculty.gg.uwyo.edu/neil/teaching/geologypics/braided.jpg) |
Now for a little rant, but first I’ll put this all in
context with my work. I work on high resolution geochemical analysis of fossil
corals and half of what I have been trying to do for the last 12 months is high resolution trace elemental analysis. For this I stick my coral stem into a machine called a
laser-ablation-inductively-coupled-mass-spectrometer (LA-ICP-MS for short),
which is a room-sized, very expensive, serious piece of kit. In short, this
machine uses a laser to vaporise the carbonate, this vapour is entrained into a gas which is
superheated to around 10,000K and ionised to form a plasma which then goes into
a mass spectrometer where the proportions of ions of various elements that
make up the sample are analysed. This is done along a tract of the coral wall, producing over 3000 readings for a sample less than 50mm long and should, in theory, let me
see seasonal changes in trace element composition allowing me to investigate
growth conditions (see this paper where they've managed to do it on modern samples). I say ‘in theory’ as I
have yet to get any meaningful data from this technique, all I have produced
are noisy squiggles of data which cannot be calibrated to any quantitative figures.
So while I can see what elements are present, I have no idea of the proportions
they are in, and thus cannot draw any conclusions, and I have no real idea why.
Now, with that in mind, you may see why Curiosity annoys me.
This little robot travels over 120 million miles through space, successfully
lands on another planet, drives around a landscape no human (and very likely
nothing else) has ever set foot on, and finds a rock (named ‘Coronation’). All
in all a very impressive feat of human engineering which we should all be proud of.
But then it, and for obvious reasons this is what I can’t deal with, it fires a
laser at the rock, ablating it and producing an ionised plasma in the exact
same way I do here, and using it’s ChemCam spectrometer it analyses the
elemental content (shown below) of said rock from the produced light spectra of the ions in
the plasma, and discovers it to have the composition of a bog-standard lump of
basalt (details here). Ok, so the rover may be analysing at a lower resolution and
using light rather than mass spectrography, but still, how can it get real,
meaningful results in space, at a distance, outside the laboratory, in a non-vacuum,
uncontrolled environment, using a machine maybe a hundredth of the size of mine, when I can’t???
Unfortunately, the answer is funding and expertise, things
NASA has a hell of a lot more than I do for my research (even with the
generosity of NERC and UEA). So, as I can’t do anything about this I’ll end
this rant with a plea; please NASA, let me be a space geologist too (as if you can’t
beat them, join them).
