ChemCam

ChemCam is a laser-induced breakdown spectroscopy (LIBS) instrument mounted on the Curiosity rover, deployed on Mars in 2012. It fires a focused infrared laser at rock and soil targets up to 7 meters away, vaporizing a small surface layer and analyzing the light emitted by the resulting plasma to determine elemental composition. The instrument combines a 1.3-megapixel camera with a spectrometer that measures emission lines across ultraviolet, visible, and near-infrared wavelengths, allowing geologists on Earth to analyze Martian geology without requiring the rover to physically contact or drill samples.

The laser itself is a Nd:KDP (neodymium potassium dihydrogen phosphate) crystal operating at 1064 nanometers in the near-infrared band. Each laser pulse lasts about 5 nanoseconds and delivers roughly 14 millijoules of energy focused to a spot roughly 400 micrometers in diameter at the target distance. The spectrometer detects light across three channels: ultraviolet (240-340 nm), visible (390-600 nm), and infrared (600-900 nm), with resolution sufficient to distinguish individual elements from hydrogen through iron in relative abundance.

Performance in Mars conditions

LIBS functions effectively in Mars' thin atmosphere (about 600 pascals, or less than 1% of Earth's pressure) because the laser creates its own localized plasma regardless of surrounding air. However, Martian dust accumulation on optics has periodically degraded performance; the rover carries cleaning brushes to maintain the camera lens. Temperature fluctuations between -125 degrees Celsius at night and 20 degrees Celsius at midday can affect laser beam stability, though the instrument includes thermal compensation systems. Dust devil storms and abrasive regolith with sharp silicate particles present ongoing maintenance challenges.

The instrument delivers qualitative elemental analysis rather than absolute quantification. Operators use calibration targets (igneous rock standards) left on the rover's deck to normalize measurements for atmospheric variation and instrumental drift, then compare unknown targets against these baselines. The technique excels at detecting light elements like carbon and hydrogen in oxidized forms, and distinguishing major rock types (basalt, andesite, igneous versus sedimentary compositions), but cannot directly measure hydrogen abundance or determine precise mineralogy without supplementary data from the rover's other instruments.

ChemCam operates as a reconnaissance tool that guides more resource-intensive analyses. When LIBS identifies a geologically interesting target, the rover can position its drill or Alpha Particle X-Ray Spectrometer (APXS) contact instrument for higher-precision measurement. This hierarchical approach maximizes scientific return given power constraints: a full analysis sequence consumes roughly 10 watt-hours per target for ChemCam alone, compared to significantly higher power demands for drilling and sample heating needed by other onboard instruments.