Electrochemical sensors, especially ion-selective electrodes, are ideally suited for analyses of extraterrestrial environments where comparatively little is known about the chemistry: they have remarkably high sensitivity over a wide dynamic range and are available for a wide range of organic and inorganic cations and anions. In addition, ion-selective electrodes require very little power, have low mass, and can withstand dramatic swings in temperature and pressure without loss of function. Analysis in exosphere environments offers unique challenges caused by the preflight preparations and storage of the sensors, the long cruise to the planetary body, and the harsh environmental conditions in which the analyses must be performed. Currently, only a single set of electrochemical analyses of another planet has been performed, but several new instruments are being developed which will potentially provide insight into the scientific questions surrounding the chemistry and biology of other planetary bodies in our solar system.

This chapter discusses the challenges of performing electrochemical analyses in an extraterrestrial environment such as Mars, with an emphasis on sensor development, characterization, and calibration while addressing lessons learned from the Phoenix mission, and looking to the future of electrochemical analyses of other planetary bodies.