Figure 1. Credit: J-L. Lacour/CEA/French Space Agency (CNES)
1. ChemCam fires a laser (solid green line) in a series of pulses at a target (rock or soil). ChemCam’s laser is powerful, but it is still invisible to the human eye. The green color of the laser depicted above is for illustrative purposes.
2. Electrons within the target become excited and emit light. The resulting flash of light is clearly visible to the human eye.
3. ChemCam receives this light (dashed green line) with a built-in telescope and it is sent down an optical fiber to the body of the rover. A spectrometer “reads” the light and identifies the types of atoms within the target. ChemCam will be able to distinguish different elements because each chemical element has its own unique “fingerprint.” Sparks from different elements and rock types also have their own color (Figure 2). Knowing which atoms are present in the target rock tells ChemCam scientists its composition.
Figure 2. Different elements, such as aluminum and copper, and rock types like basalt, give off their own color of light when zapped by a laser. Credit: Sirven et al., JAAS
Why does ChemCam use a Laser? Previous spacecraft missions to Mars, like the Spirit and Opportunity rovers, had to undertake a rather laborious, and time-consuming, task of approaching a rock, brushing away dust, and, sometimes, grinding away outer layers of rock to take a measurement of a rock’s true composition. To do all this, the rovers had to come into contact with the rock. When conducting a Mars mission, time is precious and efficiency is a necessity. It was not unheard of for Spirit and Opportunity to require two to three days to determine the composition of a rock. ChemCam’s laser removes the need to touch the rock. It allows ChemCam to determine a rock’s composition from a distance of up to 7 meters (~25 feet)! On average, the ChemCam team expects to take approximately one dozen compositional measurements of rocks per day.