VII - The Ten Instruments Mars Rover Curiosity Carries : Alpha Particle X-Ray Spectrometer
Alpha Particle X-Ray Spectrometer
NASA/JPL-Caltech/Cornell/Max Planck Institut für Chemie/University of Guelph
To get an accurate analysis of samples on Mars, the Alpha Particle X-Ray Spectrometer (APXS) works up close. When it makes contact with a rock or soil sample, it'll bombard it with alpha particles and X-rays emitted as the element curium, placed inside, decays. The rays knock electrons from the sample out of orbit, and the energy released can be measured by sensors. This much energy, you've got sodium. Count again, and you've got something else.
It works day and night, but can take a little while to get a thorough analysis: as long as two to three hours to determine all of the elements that a sample contains, although 10 minutes is enough to see the major elements at a glance.