Before we jump into a deeper discussion of how ChemCam works, let’s first define ChemCam. The ChemCam instrument is the Chemistry and Camera instrument (Figure 3), one of 10 science instruments onboard the Curiosity rover. As the name implies, ChemCam is actually two different instruments combined as one: a Laser-Induced Breakdown Spectrometer (LIBS) and a Remote Micro Imager (RMI). The purpose of the LIBS instrument is to provide elemental compositions of rock and soil, while the RMI gives ChemCam scientists high-resolution images of the sampling areas of the rocks and soil that LIBS targets.
Figure 3. ChemCam instrument. The telescope is located on the right side. Credit: ChemCam/LANL/IRAP/CNES
How does ChemCam Work? Mars is a dusty, windy planet. Dust is constantly being lifted and transported by wind through the atmosphere until it settles back to the surface where it covers everything, including rocks. ChemCam’s number one objective is to determine the composition of rocks and soil. In order to determine the true composition of a rock, the dust needs to be removed. Otherwise, the composition of the rock is mixed with the composition of the dust.
ChemCam fires its laser (Figure 4) in a series of pulses to remove the outer layer of dust. Once the dust is removed, the laser is fired again (in a series of pulses) at the exposed rock surface. These laser pulses ablate, or vaporize, the outer surface of the rock. Electrons within the atoms hit by the laser become “excited” and emit light. The energy of the light that is emitted depends on the atom. For example, excited electrons within an atom of carbon will emit light with a different energy than excited electrons within an atom of oxygen. The emitted light (from all atoms present in the rock) is received by a telescope within the ChemCam housing. From the telescope, the light enters a spectrometer through an optical fiber where it is broken down and read by the onboard computer.
Figure 4. LIBS spark on a sample of iron pyrite in the Mars sample chamber at Los Alamos National Laboratory. Credit: Los Alamos National Laboratory