Calibrating APXS on Mars

This graphic from NASA's Curiosity rover shows data obtained by the Alpha Particle X-Ray Spectrometer (APXS) from its calibration target on the 34th Martian day, or sol, of operations (Sept. 10, 2012). The graphic shows the number of counts registered in the various X-ray energy channels. Each element emits a characteristic energy, providing a signature that reveals the abundance of the element in the samples on the calibration target.

APXS, which is on Curiosity's robotic arm, analyzes chemical elements in rocks and soils. The APXS calibration target is a slab of well-characterized basaltic rock surrounded by a nickel plate. The samples were brought from Earth to compare the APXS reading in the lab prior to launch with those taken after landing on Mars. This allows scientists to monitor and to correct for any changes in the characteristics over the duration of the mission

The graph shows peaks indicating elements detected mainly from the rock slab (labeled in black) and the Martian atmosphere and the instrument itself (labeled in blue). The instrument also detected additional elements that can only belong to grains of Martian soil that were deposited onto the calibration target likely during the landing (labeled in red).

This test took place at night and the instrument performed well, confirming the pre-launch tests. Additional data were acquired around noon and in the afternoon, showing that very good performance can be achieved even during the Martian day.

Image credit: NASA/JPL-Caltech/University of Guelph