Physics Issue Investigation:

Is NASA’s CMIST mineral identification project the most suitable form of mineral identification for extra-terrestrial use?

X-Ray diffraction (XRD) is currently the tool of choice to identify alien rocks on NASA’s extra-

terrestrial expeditions.

It works on the principles of diffraction; all waves interfere with each other.

This interference causes areas of maximum interference when waves interact.

Which then produce points of light (orders) when shone through diffraction grating – a series of miniscule gaps that

case waves to visibly diffract.

These can be used to calculate the spacing between the gaps, using Bragg’s Law:

dsinθ=mλ

• Crystal atomsΘ angle of diffraction X-rays

Spacing between atoms

The same principles can be applied to crystals, using the atomic spacing's as a diffraction grating. The layers of

crystal mean that a slight modification of Bragg’s Law is required: 2dsinθ=mλ

Unfortunately, XRD requires the crystal to be ground up, destroying valuable information.

CMIST (Chromatic Mineral Identification and Surface Texture instrument) does not need the potentially irreplaceable

crystal to be destroyed.

Instead it measures every x-ray that rebounds off the whole crystal face, and converts the data to x-y

coordinates.

Which can be used to calculate the overall angle of diffraction and hence the crystal’s atomic spacing.

However this requires more computation than XRD analysis, and gives poorer resolution.

(Not actual XRD results)

The advantages and disadvantages of each method are as follows:

Criteria for extra-terrestrial use

XRD CMIST

Efficiency (power) Less efficient than CMIST Highly efficientEfficiency (time) <20 minutes VariedSize Varied (relatively compact) Large and cumbersome

(currently being refined)Durability Moderately durable Highly durableReliability Very reliable Very reliableResolution High ModeratePerformance in space-conditions

Moderate to high Theoretically very high

Specimen analysis Requires specimen to be ground up

Specimen is undamaged

Expense Moderate to high Moderate to high

Exceptional attributes of each method are shown in green, undesirable features in orange and

compromising features in red.

Current XRD models do not match the advantages of CMIST, thus although CMIST is not ready for space-travel yet, it is the most suitable form of mineral identification for extra-

terrestrial use.

Bibliography Image – slide 3: Barron, A, “Wave interference” 2010, (online) http://cnx.org/content/m38289/latest/?collection=col10699/latest Accessed 18.8.11Image – slide 4: Askill, Dr A, “Young’s double-slit diagram” 1999, (online) http://fiziks.net/Light%20Sample%20Chapter%20Three/lightsamplechapter3.htm Accessed 18.8.11Image – slide 5: Zaritsky, D, “Diffraction grating wave interference” 2008, (online) http://exoplanet.as.arizona.edu/~lclose/a302/lecture14/lecture_14.html Accessed 18.8.11Image – slide 6: Cyberphysics, “diffraction grating diagram” 2010, (online) http://www.google.com.au/imgres?q=diagram+diffraction+grating+laser&hl=en&biw=1311&bih=540&gbv=2&tbm=isch&tbnid=KEkJuIyzyodmxM:&imgrefurl=http://www.cyberphysics.co.uk/topics/light/A_level/difraction.htm&docid=SGm4cXHaktwSHM&w=300&h=368&ei=6IZZTqb0Jcj2mAWU29GuDA&zoom=1 Accessed 26.8.11Image – slide 7: Anonymous “XRD” 2006, (online) http://keterehsky.wordpress.com/page/2/ Accessed 18.8.11Image – slide 8: Smidth, F“XRD powder preparation” 2010, (online) http://www.google.com.au/imgres?q=XRD+powdered+sample+preparation2&tbm=isch&tbnid=9UjJYgturTebcM:&imgrefurl=http://www.flsmidth.com/Powders&docids2NDA&zoom=1 Accessed 28.8.11Image – slide 9: Simone, A “Moon Rock” 2008, (online) http://www.google.com.au/imgres?q=moon+rock&hl=en&biw=1086&bih=514&gbv=2&tbm=isch&tbnid=NAvVmsiUHyY3IM:&imgrefurl=http://www.clusterflock.org/2008/07/the-moon.html&docid=3_X5_o9zJoWO_M&w=650&h=450&ei=0i9aTumVH-SfmQWF6NifDA&zoom=1 Accessed 18.8.11Image – slide 10: Clark, P, “XRD and XRF analysis of Quartz” 2010, (online) http://lunarscience2010.arc.nasa.gov/cmist-next-generation-cxrdf-tool-rapid-situ-sample-characterization Accessed 10.7.11 Image – slide 11: Elliott, S “Magnetite atomic structure” 2006, (online) http://www.tyndall.ie/research/electronic-theory-group/fe3o4_calculations.html Accessed 26.8.11Image – slide 12: Anonymous “X-ray diffraction resolution comparison” 2006, (online) http://mmbr.asm.org/cgi/content/citation/75/2/268/F6 Accessed 26.8.11Image – slide 14: Anonymous “Space landscape” 2009, (online) http://www.v3wall.com/en/html/pic_down/1366_768/pic_down_6890_1366_768.html Accessed 28.8.11

Bibliography:

Bickford. C (Ed), 1973, “Geology Today” Ziff-Davies Publishing Company, Del Mar, CaliforniaDutrow. B, 2010, Louisiana State University, “X-ray powder diffraction” http://serc.carleton.edu/research_education/geochemsheets/techniques/XRD.html Accessed 22.6.11I2Mason. D, 2010, NASA official website, “The Chromatic Mineral Identification and Surface Texture Instrument (CMIST) Project Summary and Accomplishments” http://cresst.umd.edu/epo/Mason_09%20Report.pdf Accessed 20.6.11I2Serway. A, “College Physics” Saunders College Publishing, Philadelphia

By Sarah Gray258 Words (project total - 1489 words)