Mars Pathfinder APXS Oxides
Data Set Description
Table of Contents
The APXS_oxides is a listing of weight percent oxide abundances
derived from the X-ray portion of the APXS_EDR data from the Alpha
Proton X-ray Spectrometer (APXS). This data is preliminary and will
be later refined as new calibration data become available. Currently,
there are oxide results for five rocks and six soils.
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 parameters are (1) weight percent abundances of chlorine and the
oxides: Na2O, MgO, Al2O3,
SiO2, SO3, K2O, CaO, TiO2,
and FeO; (2) uncertainties on those abundances; and (3) the original
sum of the oxides before normalization. The original sum varies in
response to the measurement geometry and is closer to 100% if good
contact is made between the sample and the APXS bumper ring.
The only input necessary for processing was APXS EDR data. These data
files were the cumulative sums of data acquired from the beginning of
the measurement cycle until the final reading. Readings occurred
several times for each rock and soil that was analyzed. The first
step in processing the data is to subtract subsequent spectra from one
another and examine the deconvolved spectra to check for the
possibility of any damaged data or instrument drift (e.g. by changing
environmental temperature). The next step is to establish any changes
in energy calibration, mainly due to changes in environmental
temperature and shift the data to correct gain and zero-offset drift.
Then the individual shifted spectra are summed together. The summed
composite go into a least-squares fitting program that subtracts the
background, finds all the peaks in the spectra, and calculates the
peak areas and their uncertainties. Calibration curves (peak area
versus concentration) for each element are used to derive abundances of
each element. These calibration curves were obtained by analyzing
terrestrial samples of known composition during the APXS calibration
in the laboratory. Some corrections for matrix effects for a few of
the elements are made after this. Then, to express the element
abundances as oxide abundances, oxygen is assigned stoichiometrically
(Fe as FeO, S as SO3, etc.) and the analyses are
renormalized to an arbitrary value, in this case 98.0%.
P2O5, Cr2O3, and MnO are
not included in these preliminary results because they have large
errors and the final calibration for these has not been completed.
All of the data in this data set are contained in an ASCII tabular
file, ('OX_PERC.TAB') with a
detached PDS label ('OX_PERC.LBL').
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.
Calibration APXS measurements obtained in the laboratory.
Estimates of the locations of the 5-cm diameter spots measured on
rocks and soils on Mars are reported as XYZ coordinates in the Martian
Local Level Coordinate Frame. Only those for which the oxide
abundances have been determined are listed:
APXS
meas. |
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-7 |
4.58 |
-2.91 |
-0.18 |
Yogi rock |
| 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-15 |
-5.87 |
2.80 |
0.52 |
Mermaid dune |
| A-16 |
-3.79 |
-1.31 |
0.12 |
Wedge rock |
| A-17 |
-5.56 |
-3.25 |
-0.35 |
Shark rock |
| 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°.
The APXS oxides data can be displayed on UNIX, Macintosh, and PC
platforms using any ASCII editor.
The APXS oxides data will be stored on compact disc-read only memory
(CD-ROM) media. The CDs will be formatted according to ISO-9660 and
PDS standards. The data files will not include extended attribute
records (XARs), and will therefore not be readable on some older VMS
operating systems.
These oxide abundances are preliminary results for the X-ray portion
of the APXS_EDR data. The confidence is indicated by the
uncertainties that are assigned to each of the oxides in the
APXS_oxides ASCII table. These uncertainties were derived from the
range in differences found between recommended and measured values for
eight reference standards.
Prior to release, the data will be reviewed by the APXS instrument
team and the Planetary Data System.
The quality of the preliminary X-ray oxide abundances is indicated by
the results for Murchison C2 meteorite and the Martian meteorite
Zagami [RIEDERETAL1997B]:
| |
(1) |
(2) |
(3) |
(4) |
(5) |
| 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:
APXS
meas.
number |
Measurement initial start
time and final stop time
(Local
True Solar Time) |
Integrated
meas. time
(hrs) |
APXS spectra
accumulation time
(hrs) |
Target |
| 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'.
Further calibration and special processing is underway to improve the
conversion of X-ray data to elemental and oxide abundances, and to
calibrate the alpha and proton portions of the data and combine them
with the X-ray data.
Mission
Mars Pathfinder
Instrument Host
Mars Pathfinder Rover (Microrover Flight
Experiment)
Instrument
Alpha Proton X-ray Spectrometer
Rover Cameras
Target
PDS Welcome to the Planets:
Mars
PDS High Level Catalog:
Mars
References
MELLSTROM&LAU1996
RIEDERETAL1997A
RIEDERETAL1997B
VAUGHAN1995
WELLMAN1996B
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.