The Mössbauer Spectrometers on the science payload of the
two Mars Exploration rovers are sensitive to the oxidation and mineralogical
state of the element iron. The detector displays a spectrum as a crest or
valley according to whether the spectrometer is in transmission or
back-scatter mode. The peaks and valleys can tell which oxidation and
mineralogical states of iron are present.
Iron bonded to different elements in samples can also be detected
through Mössbauer Spectroscopy, although the energy level the iron
can absorb is not equivalent to the energy that could be absorbed by an
isolated iron atom. When the energy level to excite the iron-bearing
molecule is generated, then that cluster of atoms will absorb that energy and
emit it, which the detector will record. From the spectra, the elements
bonded to the iron can be named, even though they are not only iron.
Transition mode is one of two modes
in which the Mössbauer spectrometer can analyze samples. In this
mode, iron appears as a valley.
Back-scatter mode is the mode in
which the Mössbauer spectrometer will be used to analyze samples
on the two Mars Exploration Rovers. In this mode, iron appears as a peak.