NASA Mars Rover Curiosity: MSL Mast Camera, the Alpha Particle X-Ray Spectrometer (APXS)

In this image taken by Curiosity's Mast Camera, the Alpha Particle X-Ray Spectrometer (APXS) on NASA's Curiosity rover is pictured, with the Martian landscape in the background

Picture: REUTERS/NASA/JPL-Caltech/MSSS

The APXS (Alpha-Particle X-ray Spectrometer) for MSL is an improved version of the APXS that flew successfully on Pathfinder and the Mars Exploration Rovers Spirit and Opportunity.

The MSL APXS takes advantage of a combination of the terrestrial standard methods Particle-Induced X-ray Emission (PIXE) and X-ray Fluorescence (XRF) to determine elemental chemistry. 

It uses curium-244 sources for X-ray spectroscopy to determine the abundance of major elements down to trace elements from sodium to bromine and beyond.