Geochemists usually express the abundance of elements in rocks and minerals as weight percents of the oxides. It is a convenience that is followed because most rock forming minerals are stoichiometric compounds and it makes comparison and calculations easier. It does not mean that those specific oxides are necessarily found as minerals or compounds in the sample analyzed; it is only a way to recast the element abundances. Nor does it mean that Fe in the sample is 2+ rather than 3+. It is simply a way of expressing the chemical abundances by stoichiometric assignment to oxides. For geochemical convenience, we have recast the Pathfinder APXS elemental abundances of Na, Mg, Al, Si, S, K, Ca, Ti, Fe, and Cl to weight percent Na2O, MgO, Al2O3, SiO2, SO3, K2O, CaO, TiO2, FeO and Cl.
Further calibration is necessary to determine oxide abundances for the one other soil and four other rock measurements obtained at the Pathfinder landing site. The APXS bumper ring did not make good contact with the soil during A-9 measurements, so more testing is needed to determine the uncertainties on the oxides for this. The X-ray spectra for A-19, A-20, A-23, and A-27 rock measurements were degraded due to the rover battery death on Sol 56. The APXS_EDR data for these are available now, and oxide abundances will be determined at a later date.
The tabular file is formatted so that it may be read directly into many database management systems (DBMS) or spreadsheet programs on various computers. All fields in the table are separated by commas; text fields are left justified and numeric fields are right justified. The 'start byte' and 'bytes' values listed in the PDS label do not include the commas between fields. The records are of fixed length, and the last two bytes of each record contain the ASCII carriage return and line feed characters. This allows the table to be treated as a fixed length record file on computers that support this file type and as a normal text file on other computers.
The PDS label is object-oriented. The object to which the label refers (the TABLE) is denoted by a statement of the form:
^object = location
in which the carat character ('^', also called a pointer in this context) indicates that the object starts at the given location. For an object located outside the label file (as in this case), the location denotes the name of the file containing the object. For example:
^TABLE = 'OX_PERC.TAB'
indicates that the TABLE object is in the file OX_PERC.TAB, in the same directory as the detached label file. The detached label file is a stream format file, with a carriage return (ASCII 13) and a line feed character (ASCII 10) at the end of each record. This allows the file to be read by the MacOS, DOS, Unix, and VMS operating systems.
|X||Y||Z||Rock/Soil APXS Target|
|A-2||1.89||-1.95||0.31||soil off the end of the ramp|
|A-3||1.30||-2.45||0.18||Barnacle Bill rock|
|A-4||2.79||-2.64||0.28||soil near Yogi|
|A-5||3.29||-2.48||0.28||soil near Yogi|
|A-8||2.85||1.13||0.32||Scooby Doo indurated soil or rock|
|A-10||3.74||-0.43||0.28||dark soil next to Lamb|
|A-18||-4.81||-3.81||-0.54||Half Dome rock, first location|
The Mars Pathfinder Lander (L) Coordinate Frame
The Mars Pathfinder Lander is a tetrahedral structure. One of its faces, the one upon which it sits, is called the base petal and houses most of the lander equipment. The other three faces, or petals, open after surface impact to expose these systems. The rover is mounted on one of these petals. The Mars Pathfinder Lander Coordinate Frame, or 'L' Frame, has the lander base petal as its reference plane and its center coincident with the geometric center of the base petal. The YL-axis of this coordinate system passes through the geometric center of the rover petal, and defines the reference direction. The ZL-axis is normal to the reference plane and coincident with the nominal spacecraft spin vector. When the lander is upright on the surface, the ZL-axis is directed positively downward into the ground.
The Martian Local Level (M) Coordinate Frame
The Martian Local Level Coordinate Frame is a right handed, orthogonal, frame whose origin is co-incident with the origin of the Lander Coordinate Frame. The XM axis points north, the YM axis points east, and the ZM axis points down.
For more information on Mars Pathfinder coordinate systems, see the [MELLSTROM&LAU1996], [WELLMAN1996B], and [VAUGHAN1995] references. However, please note that as of the time this APXDDRDS.CAT file was written, [WELLMAN1996B] had not yet updated his discussion of elevation measurements to match that agreed upon by the Project. Where he used elevation ranges of 0° to 180°, the MPF Project used -90° to +90°.
|Na2O||2.3||0.7 to 1.2||1.5||0.7||0.2|
|MgO||8.8||8.6 to 11.6||18.2||18.2||19.9|
|Al2O3||7.1||4.8 to 6.2||2.4||2.3||2.3|
|SiO2||49.6||48.4 to 50.9||31.0||31.0||28.5|
|SO3||0.3||0.15 to 0.29||7.8||7.8||7.9|
|K2O||0.25||0.13 to 0.24||0.06||0.04||0.04|
|CaO||10.9||9.7 to 11.1||2.0||1.8||1.9|
|TiO2||1.0||0.74 to 1.4||0.04||----||0.06|
|FeO||17.4||18.0 to 24.5||30.2||30.2||27.1|
(1) Zagami Martian meteorite rock slice, APXS analysis for a counting time of 127,470 seconds. (2) Zagami Martian meteorite, five individual chips of about 0.5 g each, measured using instrumental neutron activation analysis (INAA), X-ray fluorescence (XRF) and carbon-sulfur analyzer (GSA) at Max-Planck Institut fur Chemie. (3) powdered Murchison C2 meteorite, measured using an APXS for a counting time of 242,030 seconds. (4) powdered Murchison C2 meteorite, measured using an APXS for a counting time of 20,360 seconds. (5) powdered Murchison C2 meteorite, measured using INAA, XRF and GSA at Max-Planck Institut fur Chemie.
Results for the soil A-2 are not as good as the others, due to poor contact with the sample by the APXS deployment mechanism and lower counting rates for alpha particles, protons, and X-rays. This is reflected in the lower original sum of the oxides for A-2.
When measuring rock and soil samples, the desire was to obtain at least 10 integrated hours. Only 3 hours of nighttime measurement were needed for a good X-ray analysis. X-ray spectra obtained during the night, when ambient surface temperatures were low, were unaffected by electronics noise. Ten hours of measurement during the day or night provide good alpha and proton analyses. Shorter times still provide useful results. The measurement times for the 11 APXS measurements that have been converted to oxide abundances are shown below:
|Measurement initial start
time and final stop time
(Local True Solar Time)
|A-2||Sol 2 14:53 - Sol 3 10:00||19.6||15.9||soil|
|A-3||Sol 3 15:00 - Sol 4 07:01||16.5||13.6||rock|
|A-4||Sol 4 16:59 - Sol 5 01:32||8.8||8.1||soil|
|A-5||Sol 5 16:01 - Sol 6 06:55||15.3||9.2||soil|
|A-7||Sol 10 14:17 - Sol 11 02:37||12.7||5.7||rock|
|A-8||Sol 14 14:03 - Sol 15 02:55||13.2||5.7||soil|
|A-10||Sol 20 14:03 - Sol 21 02:59||8.3||7.0||soil|
|A-15||Sol 28 14:05 - Sol 29 02:44||8.0||5.3||soil|
|A-16||Sol 37 14:07 - Sol 38 03:05||8.2||6.5||rock|
|A-17||Sol 52 14:18 - Sol 53 03:05||8.0||7.0||rock|
|A-18||Sol 55 14:06 - Sol 56 00:05||7.2||5.9||rock|
Measurement initial start and stop times were obtained from the SCLK times in the downlink telemetry for the acknowledgement of the exact commands that were issued to trigger the start and stop of each APXS measurement (usually Meas_Start, Meas_Stop, Reset, or Shutdown). SCLK times were converted to Local True Solar Time using the script sclk2ltmst (see Ancillary Data discussion). This time is only as accurate as the rover's clock, and is a close approximation to the exact initial start and stop time of each APXS measurement. In a few cases, the downlink was lost, and uplink predictions were used instead. Some of the cumulative APXS measurements were interrupted by other rover activities, in which case, the first accumulation start time and last stop time are indicated. Integrated measurement time, as indicated by ALPHA_SAMPLING_DURATION, PROTON_SAMPLING_DURATION, and XRAY_SAMPLING_DURATION in the data file headers, is always less than the accumulation final stop time minus the initial start time, because the sampling durations do not include quiet periods when the APXS was powered off and detector 'dead time'.