Moessbauer (MB) spectroscopy is a powerful tool for quantitative mineralogical analysis of Fe-bearing materials. The miniature MB spectrometer MIMOS II is a component of the Athena science payload to be launched to Mars in 2003 on both Mars Exploration Rover missions. The instrument has two major components: (1) a rover-based electronics board which contains power supplies, a dedicated central processing unit, memory, and associated support electronics and (2) a sensor head that is mounted at the end of the instrument deployment device (IDD) for placement of the instrument in physical contact with soil and rock. The velocity transducer operates at a nominal frequency of ~25 Hz and is configured with two 57Co/Rh MB sources. One source (~5 mCi landed intensity), together with a reference target (alpha-Fe2O3 plus alpha-Fe0) and PIN diode detector in transmission geometry, are internal to the sensor head and is used for instrument calibration. The other source (~150 mCi landed intensity), together with four PIN diodes in backscatter measurement geometry, irradiates Martian surface materials with a beam diameter of ~1.4 cm after passing through a collimator. Physical contact with surface materials is sensed with a switch-activated contact plate. The contact plate and internal reference target are instrumented with temperature sensors. Assuming ~18% Fe for Martian surface materials, experiment time is 6-12 hours during the night for quality spectra (i.e., good counting statistics); 1-2 hours is sufficient to identify and quantify the most abundant Fe-bearing phases. Data stored internal to the instrument for selectable return to Earth include MB and pulse-height analysis spectra (256 channels each) for each of the five detectors in up to 13 temperature intervals (65 MB spectra), engineering data for the velocity transducer, and temperature measurements. The total data volume is ~150 kByte. The mass and power consumption are ~500 g (~400g for the sensor head) and ~2 W, respectively. The scientific measurement objectives of the MB investigation are to obtain for rock, soil, and dust (1) the mineralogical identification of iron-bearing phases (e.g., oxides, silicates, sulfides, sulfates, and carbonates), (2) the quantitative measurement of the distribution of iron among these iron-bearing phases (e.g., the relative proportions of iron in olivine, pyroxenes, ilmenite and magnetite in a basalt), and (3) the quantitative measurement of the distribution of iron among its oxidation states (e.g., Fe2+, Fe3+, and Fe6+). Special geologic targets of the MB investigation are dust collected by the Athena magnets and exterior and interior rock and soil surfaces exposed by the Athena Rock Abrasion Tool and by trenching with rover wheels, respectively.

Klingelhoefer, G., et al., The Athena MIMOS II Moessbauer Spectrometer
                   Investigation, Journal of Geophysical Research, 2003.

Instrument Overview
  ===================
    Moessbauer (MB) spectroscopy is a powerful tool for quantitative
    mineralogical analysis of Fe-bearing materials. The miniature
    MB spectrometer MIMOS II is a component of the Athena
    science payload to be launched to Mars in 2003 on both Mars
    Exploration Rover missions. The instrument has two major
    components: (1) a rover-based electronics board which contains
    power supplies, a dedicated central processing unit, memory,
    and associated support electronics and (2) a sensor head that
    is mounted at the end of the instrument deployment device (IDD)
    for placement of the instrument in physical contact with soil
    and rock. The velocity transducer operates at a nominal
    frequency of ~25 Hz and is configured with two 57Co/Rh MB
    sources. One source (~5 mCi landed intensity), together with a
    reference target (alpha-Fe2O3 plus alpha-Fe0) and PIN diode
    detector in transmission geometry, are internal to the sensor
    head and is used for instrument calibration. The other source
    (~150 mCi landed intensity), together with four PIN diodes in
    backscatter measurement geometry, irradiates Martian surface
    materials with a beam diameter of ~1.4 cm after passing through
    a collimator. Physical contact with surface materials is sensed
    with a switch-activated contact plate. The contact plate and
    internal reference target are instrumented with temperature
    sensors. Assuming ~18% Fe for Martian surface materials,
    experiment time is 6-12 hours during the night for quality
    spectra (i.e., good counting statistics); 1-2 hours is sufficient
    to identify and quantify the most abundant Fe-bearing phases.
    Data stored internal to the instrument for selectable return to
    Earth include MB and pulse-height analysis spectra (256 channels
    each) for each of the five detectors in up to 13 temperature
    intervals (65 MB spectra), engineering data for the velocity
    transducer, and temperature measurements. The total data volume
    is ~150 kByte. The mass and power consumption are ~500 g (~400g
    for the sensor head) and ~2 W, respectively.
 
    The scientific measurement objectives of the MB investigation are
    to obtain for rock, soil, and dust (1) the mineralogical
    identification of iron-bearing phases (e.g., oxides, silicates,
    sulfides, sulfates, and carbonates), (2) the quantitative
    measurement of the distribution of iron among these iron-bearing
    phases (e.g., the relative proportions of iron in olivine,
    pyroxenes, ilmenite and magnetite in a basalt), and (3) the
    quantitative measurement of the distribution of iron among its
    oxidation states (e.g., Fe2+, Fe3+, and Fe6+). Special geologic
    targets of the MB investigation are dust collected by the
    Athena magnets and exterior and interior rock and soil surfaces
    exposed by the Athena Rock Abrasion Tool and by trenching with rover
    wheels, respectively.
 
    Information in this instrument description is taken from The Athena
    MIMOS II MB Spectrometer Investigation paper
    [KLINGELHOEFERETAL2003]. See this paper for more details.
 
 
  Scientific Objectives
  =====================
    The chief scientific objectives of the MB are:
 
    1) to identify iron-bearing mineral phases (e.g., oxides, silicates,
       sulfides, sulfates, and carbonates), in rock, soil, and dust,
 
    2) to quantitatively measure the distribution of iron among these
       iron-bearing phases (e.g., the relative proportions of iron in
       olivine, pyroxenes, ilmenite and magnetite in a basalt),
 
    3) to quantitatively measure the distribution of iron among its
       oxidation states (e.g., Fe2+, Fe3+, and Fe6+), and
 
    4) to distinguish between magnetically ordered and paramagnetic
       phases and provide, from measurements at different temperatures,
       information on the size distribution of magnetic particles.
 
 
  Calibration
  ===========
    It is necessary to calibrate both the drive velocity and the
    detectors of the MB. The interpretation of acquired MB spectra is
    impossible without knowing the drive velocity precisely at any given
    time. MB drive velocity calibration for MIMOS II is rather
    straightforward and done in three different ways, thus ensuring
    redundancy. Prior to flight each individual drive system was
    calibrated by measuring in backscattering mode an alpha-iron foil
    standard. A maximum drive velocity was preset by firmware. Fitting
    the acquired MB spectrum using the well known parameters of the
    alpha-iron foil then yielded the real velocity. This procedure was
    repeated at different temperatures.
 
    During the mission, the magnetite CCT (Compositional Calibration
    Target) will be measured in several runs to verify the functionality
    of MIMOS II. The well known MB parameters of magnetite can be used
    for velocity calibration again. These kind of measurements have been
    done already in the lab with the flight units as a function of
    temperature, to be used as reference for the measurements on Mars.
 
    The primary method for velocity calibration is the internal
    reference target and detector configured in transmission measurement
    geometry. The reference target is a mixture of alpha-Fe0 (metallic
    iron, 30% enriched 57Fe) and alpha-Fe2O3 (hematite, 95% enriched
    57Fe), and its MB spectrum is measured automatically during each
    backscattering measurement. Each component of the reference target
    has well-known MB parameters, so that fitting of reference spectra
    enables velocity calibration for each individual measurement done in
    backscatter geometry, ensuring that the actual drive velocity is
    always well-defined, regardless of prevailing environmental
    conditions.
 
    Careful energy calibration on each detector was done to achieve
    optimal detection rate. Each sensor head was temperature cycled
    (153K  293K). During cycling, energy spectra were measured. As a
    result of analysis of these spectra, optimal firmware parameters
    were calculated for each detector and each temperature window.
    During operation, instrument firmware will adjust those parameter
    depending on temperature, thus ensuring best detector performance.
 
 
  Operational Considerations
  ==========================
    Targets for MB analysis for the mineralogical composition of
    Fe-bearing phases, the relative distribution of Fe and its oxidation
    states among those phases, are the exposed surfaces of soil and
    rock, interior regions of rock exposed by the Rock Abrasion Tool,
    subsurface soil exposed by trenching, and the two magnets mounted on
    the rover deck. In the case of the magnets, it is know from Viking
    and Mars Pathfinder that Martian aeolian dust is magnetic, but the
    composition of the magnetic phase or phases is not known. When the
    dust buildup on the magnets is sufficiently large, as determined
    using Pancam, the IDD will be used to place MIMOS II directly
    against the magnets, providing what should be a definitive
    identification of the magnetic phases present. Fine-grained material
    produced by the RAT, if present in sufficient lateral extent and
    depth, provides a target that is representative of the volume
    excavated and for which orientation effects are likely not present.
    The relatively high penetration depth of the 14.4 keV MB radiation
    means that it may be possible to obtain mineralogical information
    about unaltered rock without removing exterior rinds or dust
    coverings with the RAT.
 
    The MB is a less contamination sensitive to dust than the APXS or
    the Microscopic Imager, which are the other two instruments on the
    IDD. Therefore, for soft and/or dirty targets the MIMOS II contact
    sensor may sometimes be used as a 'blind man's cane', helping to
    establish target location in IDD coordinates so that the other
    instruments can be placed with less risk of contamination.
 
    In some instances, it may be possible for MIMOS II to achieve a
    signal-to-noise ratio that is adequate for answering key scientific
    questions in a time much less than the nominal experiment time of
    6-12 hr during the overnight period. This will be particularly true
    early in the mission when radiation source strength is greatest, and
    for targets with high Fe contents. Where appropriate, then, the MB
    may be used in a 'touch and go' mode, in which a short integration
    is performed at the start of a sol, followed by other rover
    activities that may include driving.
 
 
  Detectors and Electronics
  =========================
    The main disadvantage of the backscatter measurement geometry
    employed by MIMOS II is the secondary radiation caused by primary
    122 keV radiation from the decay of 57Co. To reduce the background
    at the energies of the 14.4 keV gamma-ray and the 6.4 keV X-ray
    lines, a detector with good energy resolution is required. In
    addition, an intense main 57Co source and a detector system covering
    a large solid angle are needed to minimize data acquisition time.
    Good resolution is even more important should it prove possible to
    use these detectors for elemental analysis with the X-ray
    fluorescence technique (i.e., using the pulse height analysis (PHA)
    spectra that are also acquired as a part of our measurement
    procedure). For this reason, four Si-PIN-diodes with a 10 x 10 mm2
    active area were selected as detectors instead of gas-counters. A
    detector thickness of about 400-500 um is a good choice according to
    calculations and experience. The energy resolution is ~1.0-1.5 keV
    at room temperture, and it improves at lower temperaures. The
    efficiencies at 6.4 and 14.4 keV are nearly 100 % and about 70 %,
    respectively.
 
    The 100 V DC bias voltage for the detector diodes is generated by
    high frequency cascade circuitry with a power consumption of less
    than 5 mW. Noise contributions are minimized by incorporating a
    preamplifier-amplifier-SCA system for each individual detector.
 
    In addition to the four detectors used to detect backscattered
    radiation from the sample, there is a fifth detector to measure the
    transmission spectrum of the reference absorber (alpha-57Fe plus
    alpha-57Fe2O3 Sample and reference spectra are recorded
    simultaneously, and the known temperature dependence of the MB
    parameters of the reference absorber can be used to give a
    measurement of the average temperature inside the sensor head,
    providing a redundancy to measurements made with the internal
    temperature sensor.
 
    MIMOS II has three temperature sensors: one on the electronics board
    in the Rover warm electronics box and two on the sensor head
    (Analogue Devices AD590). One temperature sensor in the sensor head
    is mounted near the internal reference absorber, and the measured
    temperature is associated with the reference absorber and the
    internal volume of the sensor head. The other sensor is mounted
    outside the sensor head at the contact ring assembly. It gives the
    approximate analysis temperature for the sample on the Martian
    surface. This temperature is used to route the MB data to the
    different temperature intervals (maximum of 13, with the temperature
    width software selectable) assigned in memory areas. In case of
    contact-ring temperature sensor failure, the internal temperature
    sensor would be used (software selectable).
 
    During measurements, a temperature log is acquired for all
    three sensors. Temperature measurements are done approximately every
    5 min (software selectable: min ~10 sec, max ~40 min). MIMOS II can
    accumulate up to 256 temperature records corresponding to a total
    integration time of ~21 hours.
 
    The electronics in the rover body include an internal
    microcontroller, so that the instrument can collect data
    independently of the rover computer. The analog signals of the five
    detector channels are analyzed by discriminators for 14.4 keV and
    6.4 keV peaks. MB spectra for the two different energies of 6.4 keV
    and 14.41 keV are sampled separately.
 
 
  Location
  ========
    The MB is mounted on the end of the IDD.
 
 
  Measured Parameters
  ===================
    The Athena Mossbauer spectrometer uses a vibrationally-modulated
    57Co source to illuminate target materials. Backscattered gamma
    signals are binned according to the source velocity, revealing
    hyperfine splitting of 57Fe nuclear levels that provides
    mineralogical information about the target.

extracted metadata from PDS3 catalog and
                    modified to comply with PDS4 Information Model

MER-Opportunity Moessbauer Spectrometer

Description

Identifier (LID)

Version