The Thermal and Evolved Gas Analyzer (TEGA) on the Mars Phoenix Lander is composed of two separate components which are closely coupled: a Scanning Calorimeter (SC) and a mass spectrometer as an Evolved Gas Analyzer (EGA). TEGA has the capability of performing scanning calorimetry on eight small soil samples selected in the vicinity of the lander. The samples will be heated in ovens to temperatures up to 1000C, and the volatile compounds (e.g.water and carbon dioxide), which are released during the heating, will be analyzed in the EGA. The power required by the sample oven is continuously monitored during the heating, allowing analysis of both endothermic and exothermic phase transitions, which can be used to identify the phases present. By correlating the gas release with the calorimetry, the abundance and composition of the volatile compounds associated with the different phases can be determined. The EGA mass spectrometer is sensitive to detection levels down to 10 parts per billion, a level that may detect minute quantities of organic molecules potentially existing in the ice and soil.

Boynton, W. V., H. Enos, C. Fellows, D. K. Hamara, K. Harshman, M. S. Williams,
                   M. R. Fitzgibbon, M. Finch, G. Droege, J. Hoffman, D. W. Ming, and P. Niles,
                   The Thermal and Evolved-Gas Analyzer on the Phoenix Mars Lander, J. Geophys.
                   Res., in prep.

Instrument Overview
  ===================
    The Thermal and Evolved Gas Analyzer (TEGA) on the Mars Phoenix
    Lander is composed of two separate components which are closely
    coupled: a Scanning Calorimeter (SC) and a mass spectrometer as
    an Evolved Gas Analyzer (EGA). TEGA has the capability of
    performing scanning calorimetry on eight small soil samples
    selected in the vicinity of the lander. The samples will be
    heated in ovens to temperatures up to 1000C, and the volatile
    compounds (e.g.water and carbon dioxide), which are released
    during the heating, will be analyzed in the EGA. The power
    required by the sample oven is continuously
    monitored during the heating, allowing analysis of both
    endothermic and exothermic phase transitions, which can be used
    to identify the phases present. By correlating the gas release
    with the calorimetry, the abundance and composition of the
    volatile compounds associated with the different phases can be
    determined. The EGA mass spectrometer is sensitive to detection
    levels down to 10 parts per billion, a level that may detect
    minute quantities of organic molecules potentially existing in
    the ice and soil. Please see [BOYNTONETAL2008] for a
    comprehensive descrition of the TEGA instrument.
 
 
  Scientific Objectives
  =====================
    The main scientific objectives of TEGA are to determine the
    abundance of climatologically important compounds (e.g. water,
    carbon dioxide) in the Martian soil, and to determine the
    mineral phases with which they are associated.TEGA. TEGA will
    also be looking for traces of organic material that may
    potentially exist. Additionally,the EGA mass spectrometer will
    perform measurements of atmospheric constituent abundances and
    isotopic ratios.
 
 
  Operational Considerations
  ==========================
    TEGA is well suited to analyze the important volatile
    constituents water and carbon dioxide. It combines two
    instruments, a thermal analyzer and an evolved gas analyzer,
    to make a synergistic analysis of the amount of volatiles in the
    soil and the mineral phases with which they are associated.
 
    The eight thermal analyzers that compose TEGA are scanning
    calorimeters (SC). After being filed with sample, each oven is
    heated according to a programmed temperature ramp, and the heat
    needed to maintain the oven at the ramp temperature is monitored.
    The heat required by the sample is attributed to that needed to
    heat the sample at the commanded temperature ramp. The output of
    the instrument is simply the heat flow to the oven plotted as a
    function of time (or temperature).
 
    When a phase transition occurs, the enthalpy associated with the
    transition will be noted in the output. If the transition is
    endothermic, for example, the melting of ice, the heat required
    to effect the melting, 334 J/g, will be added to the sample oven
    as the sample is heated past the ice melting point. This heat is
    in addition to that required by the heat capacity of the sample
    and results in a positive peak in the output. In contrast, if
    there is an exothermic transition, the sample will require less
    heat than otherwise, and a negative peak in the output will be
    observed. In both cases the area of the peak is equal to the
    enthalpy (deltaH) of the reaction.
 
    While the sample is being heated, a carrier gas of N2 is passed
    through the ovens to transport any evolved gases to the EGA. The
    EGA continuously monitors the gas stream, and the output is time
    correlated to the SC output in order to associate gas release
    with any observed phase transitions.
 
    The EGA consists of magnetic sector-field mass spectrometer. The
    key EGA mass spectrometer instrument parameters are as follows:
 
        Mass analyzer:    Magnetic sector-field.
        Electron source:  Thermal emission type.
        Mass ranges:      4 - extending from 0.7 Da to 140 Da.
                                    Channel 1 - 0.7-4 Da,
                                    Channel 2 - 7-35 Da,
                                    Channel 3 - 14-70 Da
                                    Channel 4 - 28-140 Da.
        Mass resolution:  M/deltaM = 140
                                (highest mass range- others
                                appropriate to the mass range)
        Volume:           9.5 x 9 x 7  inches
        Mass:             5.7 kg.
        Operating Power:  13 watts
 
     The EGA measures relative abundances of evolved gases and the
     isotopic ratios of its principal constituents. In addition to
     measuring evolved gasses the EGA mass spectrometer makes two
     different kinds of atmospheric measurements. The atmosphere is
     sampled through a constricted flow tube to measure the relative
     abundances and isotopic ratios of carbon, nitrogen, oxygen,
     hydrogen and argon. Atmospheric samples are also collected in
     the Gas Enrichment Cell. The atmospheric sample is admitted to
     a small volume. A getter removes active gases increasing the
     partial pressure of noble gases sixty times. The sample is then
     admitted to EGA mass spectrometer to measure noble gas isotopic
     ratios and methane.
 
 
  Calibration
  ===========
    Calibration information for the TEGA instrument is provided
    in the TEGA Calibration Report (calib/tega_calibration_report.pdf).
 
 
  Operational Modes
  =================
    The TA assembly has several modes of operation. First the TA is
    operated with the oven empty and open. As the oven is filled with
    sample, the sample fill mechanisms and the sample fill indicator
    LED are operational. Once the oven is full, it is closed, and the
    oven heating portion of the operations begins. Heating continues
    until a maximum temperature is reached and sample is finished
    evolving gasses.
 
    The EGA has two operational modes, sweep mode and mass hopping
    mode. In sweep mode, the EGA collects count data in four channels
    with discrete mass ranges. In mass hopping mode, the EGA collects
    counts in 5 or 7 contiguous masses, then hops to the next mass
    peak area of interest, thus ignoring uninteresting protions of the
    mass spectrum.

Phoenix Thermal and Evolved Gas Analyzer

Description

Identifier (LID)

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