Innovation: the success story of CheMin

Yesterday's telecon helped to put into perspective the importance of what the Curiosity team has done; the first off-world spectroscopic analysis of extraterrestrial material using an X-ray diffraction instrument. And if that isn't enough, this instrument usually occupies a space equal to your average modern fridge! How do you lug such a thing to Mars? The only way out is to miniaturise it (my parents keep complaining about how the buttons on their phones keep getting smaller with every model. I don't hear them complaining now that there aren't anymore!).

Progress; from room size to the CheMin (circled in orange right above) and ultimately spinoffs for mining and research (yep, the orange case is it! ) (NASA/Ames/JPL-Caltech)

CheMin's story is reminiscent of the progress computers have gone through over the past few decades ('a computer in every home?! You're crap' so they told Bill Gates). Miniaturisation is the endgame in technology and it demands innovation in design and even the way we think and consider reality. Now thanks to NASA's work, CheMin's spinoffs are available for a diverse number of uses including mining and HIV/AIDS virus research. In other words space pays off. Big time! (It is interesting to note that NASA does allow scientists to earn royalties from patented designs).

So how does it work? First we must remind ourselves some physics; X-ray is light in a manner of speaking. It is the second strongest 'light' in the electromagnetic spectrum. And like ordinary white light, it can undergo something called diffraction. This is the ability of a beam or a wave of any sort for that matter (like electromagnetic ones) to spread out when they pass through an aperture. Now when that happens to light (which is a mixture of wavelengths) the spread out waves give us the colours of the rainbow.

Diffration (Commons)

Now CheMin is all about diffraction. It actually takes 10mm cube of sample with 65mm cube in reserve in powdered form and puts this powder in the path of a laser beam. The beam, like the waves in the animation to the left of this passage, are spread out and the resulting image of the spread out waves (which we cannot see for obvious reasons) is recorded by a charged coupled device or CCD (another nifty gadget with NASA pedigree) which acts like an electric equivalent of our eyes' retina, recording the position as well as energy/frequncy of 99% of all the photons that strike it. It is a single-photon counting mode that ensures that a single pixel records a 1 or 0 value i.e. a photon or no photon. The X-rays are produced by a Cobalt source that is bombarded by electrons to excite it into emitting them. These rays are very energetic and anything producing or absorbing them needs to be cooled down to -60 degrees celsius. And that's important because they need to do these sessions for up to 10hrs (these can be divided up to save time and energy). Doing it at night also helps with the heating problem because its much colder then than during the day.

But hey! What's causing the X-ray beam to diffract? The powdery sample contains crystals with a maximum size of not more than 150microns. These crystals have regular crystal framework which acts like an aperture wonderland. The X-ray photons are spread out in a defined way which is dependent on the arrangement of the crystal's many atoms. It is this regular pattern of diffracting and interfering waves that allows scientists to know exactly what material they're handling and actually measure concentrations and ratios accurately for mineralogical identification (CheMin's CCD can also see the fluorescence (glow) that comes out of sample while it is being hit with X-rays allowing scientists to detect elements in the sample greater heavier than sodium in the periodic table).

And that is exactly what CheMin sent back to Earth:

The CheMin X-ray scattering pattern for Rocknest material (NASA/Ames/JPL-Caltech)

The data can also be plotted by the counts (the number photons) against the energy of the photon although they didn't do so here. They detected feldspar, pyroxenes and olivine. The latter 2 make up most volcanic rocks. The speakers at the telecon compared the sample's signature to the volcanic material on the slopes of Mauna Kea in Hawaii although there is a signature showing that 50% is amorphous or non-crystalline material that doesn't seem to be easily explainable and they would have to do more research to find out what exactly is it. No water evidence (yet) if you having trouble following.

So that was pretty much that. The Q&A session saw a lot of queries on methane results from Curiosity. Project scientist John Grotzinger said he had nothing to say on that matter but said that it might be addressed next week (no people this ain't no conspiracy it's just that they're not yet ready for press).

The sample cells that hold the sample in the path of the X-ray number 27 which can be reused so for a mission that is set to last well beyond 2 years CheMin's future on Mars looks fairly secure for now. Five of them carry standard materials for calibration purposes including ceramics and quartz. The cells ride a wheel that can rotate 185 degrees to receive samples that's dropped from the funnels to the waiting cells. Each pair of connected cells vibrate to move the sample grains around so that all of them get a chance to say cheese for the X-ray beam with their best 'sides'. It is actually this vibration system that revolutionised CheMin because it allowed the powdered materials to be handled with very few moving parts.

CheMin's pair of cells (NASA/Ames/JPL)

I'll leave it here now with this video of the instrument's principal investigator Dr. David Blake giving a demo of CheMin. Stay curious now y'hear?



For the nerdy type, there plenty more to read about this instrument here.