Current Science Data
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This figure shows RSS acceleration from
the three Pathfinder science acceleromaters plotted as a function of time during the
Pathfinder spacecraft landing. Specific features are airbag deployment (1194 seconds), RAD
motor firing (1198 seconds), the cutting of the bridal (1200 seconds), the first bounce
(1204 seconds), and the second bounce (1210 seconds). 15 bounces are clearly shown before
the high rate (32 Hz) data sampling period ends. Pathfinder is thought to have bounced and
rolled for another 1 minute before coming to rest. The height of the peak shows how hard
the lander bounced, and the time between peaks shows how high the bounce was (For example
6 seconds =3D 16.7 m, 5 seconds =3D 11.6 m, 4 seconds =3D 7.4 m, 3 seconds =3D 4.2 m, and
2 seconds =3D 1.9 m). |
This figure shows the variation with
time of pressure (dots) measured by the Pathfinder MET instrument during landing period of
Figure 1. The two diamonds indicate the times of bridal cutting and 1st impact. The
overall trend in the data is of pressure increasing with time. This is almost certaily due
to the lander rolling downhill by roughly 10 m. The spacing of the horizontal dotted lines
indicates the pressure change expected from 10 m changes in altitude. Bounces may also be
visible in the data. |
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This figure shows the signature of a
dust devil that passed over the Pathfinder lander on Sol 25. Since then we have seen
several similar features. The black line shows surface pressure plotted over a period of
approximately two minutes. The sharp minimum approximately 0.5% below the background
pressure is very clear. The dashed curves show raw data from two hot wire wind sensor
elements (Blue =3D Wind Sensor 4 =3D East Wind, Red =3D= Wind Sensor 1 =3D West Wind).
When the wind blows directly on an element it cools==2E. It is clear from the figure that
the East wind increases suddenly as the dust devil approaches the lander and the pressure
begins to fall. As the dust devil passes over the lander, pressure begins to rise, the
East wind dies away and the West wind increases suddenly. Finally as the dust devil moves
away, pressure returns to normal and the West wind dies away. This is a textbook
dust-devil signature. |
This figure is a very simplified schematic drawing of the
dust-devil that passed over the Sagan Memorial Station on Sol 25. It shows direction of
motion and the graphs of a textbook dust-devil in terms of wind speed and surface
pressure. |
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In this diagram, preliminary Pathfinder APXS analyses of soils (yellow dots) extend the
range of Viking soil analyses. The analysis of Yogi appears to be contaminated by dust
adhering to the rock's surface. The rock composition can be estimated by subtracting a
portion of dust; the resulting Yogi composition is very similar to that of Barnacle Bill
(we assumed 50% dust having the composition of drift analysis A-5 and used a linear mixing
model to subtract the dust which is only strictly valid if the dust, where present, is
thicker than the APXS penetration depth). Barnacle Bill is also contaminated by dust, but
to a lesser extent. |
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APXS analyses of Martian soils are compared with Viking soil analyses. Each element is
normalized to silicon in this diagram. The yellow boxes representing Viking data include
all analyses and their analytical uncertainties reported by B.C. Clark and others (1982)
Journal of Geophysical Research, vol. 87, p. 10,064. Although the first APXS soil analysis
(A-2) was reported to be almost identical to Viking soils, ssubsequent analyses
demonstrate some variability and a few significant differences from Viking analyses.
Specifically, soils at the Pathfinder site generally have higher aluminum and magnesium,
and lower iron, chlorine, and sulfur. Scooby Doo, which appears to be a sedimentary rock
composed primarily of compacted soil, also exhibits a few chemical differences form the
surrounding soils. Analysis A-5 represents a deposit of windblown dust (called drift),
whereas the other soil analyses may be cemented materials. |
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This diagram (preliminary X-ray data) illustrates chemical differences between
terrestrial rocks and meteorites inferred to have been derived from Mars. The Martian
meteorites (as well as Viking soil analyses) all plot to the left of the fields for Earth
rocks. Pathfinder APXS analyses of rocks (stars) and soils (yellow dots) appear to plot in
the gap between these previously defined fields, although they are similar to at least one
basaltic meteorite. The other two stars represent the compositions of Barnacle Bill and
Yogi. The analysis of Yogi appears to be contaminated by dust adhering to the rock's
surface. The rock composition can be estimated by subtracting a portion of dust; the
resulting Yogi composition is very similar to that of Barnacle Bill (we have assumed 50%
dust having the composition of drift analysis A-5 and used a linear mixing model to
subtract the dust which is only strictly valid if the dust, where present, is thicker than
the APXS penetration depth). Barnacle Bill is also contaminated by dust, but to a lesser
extent. |
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The Pathfinder APXS chemical analyses of Barnacle Bill and Yogi (corrected for adhering
dust) have been recast into plausible minerals using the CIPW norm calculation. If they
are fully crystalline igneous rocks, both possibly consist of orthopyroxene
(magnesium-iron silicate), feldspars (aluminum silicates of potassium, sodium, and
calcium), quartz (silicon dioxide), and other minerals that include magnetite, ilmenite,
iron sulfide, and calcium phosphate. |
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This commonly used chemical classification for lavas shows that Barnacle Bill and Yogi
(corrected for adhering dust) are distinct from basaltic Martian meteorites (shown as red
squares). The Pathfinder APXS analyses have been corrected fo the presence of a small
amount of salt, and sulfur is assumed to be present as sulfide. These rocks plot in or
near the field of andesites, a type of lava common at continental margins on the Earth.
The preliminary data for alkalis are likely to represent upper limits, so refinement of
these analyses could shift them to slightly lower Na2O + K2O and higher SiO2. We do not
presently know whether these are igneous (crystallized from a melt), sedimentary
(grains/fragments deposited by wind or water or precipitates), or metamorphic rocks
(deformed). |
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The surface near the rover's egress
from the lander contains bright red drift (#1), dark gray rocks such as Cradle (#3), soil
intermediate in color to the rocks and drift (#2), and dark red soil on and around the
rock Lamb (#4). Globally, Mars is characterized by similar color variations. The spectra
of these sites have been ratioed to the drift to highlight their differences. The rocks
are less red and have less of a bend in the spectrum at visible wavelengths, indicating
less ferric minerals and a more unweathered composition than drift. The intermediate
colored soils appear intermediate in the spectral properties as well. The dark red soil at
Lamb is darker than drift by about equally as red; the curvature of sppectrum at visible
wavelengths indicates either more ferric minerals or a larger particle size. The surface near the rover's egress from the lander contains mainly bright
red drift (#1), dark gray rocks such as Cradle (#3), soil intermediate in color to the
rocks and drift (#2), and dark red soil on and around the rock Lamb (#4). Globally, Mars
is characterized by similar color variations. The spectra, measured using the full 13-
color capability of IMP, provide evidence for the mineralogy of the unweathered rocks and
highly weathered red soils. |
The first color panorama returned by
IMP after Mars Pathfinder's landing included several larger, gray rocks, bright red dust
on a flat- topped rock and the ground between the rocks, and darker red soil exposed where
Pathfinder's landing dislodged a small rock. The less red color and low reflectance of the
rocks is consistent with the iron minerals found in igneous rocks, whereas the fine,
bright drift has a spectrum indicative of a weathering product. The strength of the bend,
or "kink", in the spectrum is related to the abundance and particle size of
specific crustalline, ferric weathering products. In the false color image, the blue areas
have a weak kink and are relatively unweathered, whereas the red areas' strong kink
indicates an abundance of ferric iron minerals. Rocks and
soils on the surface are thought to be composed of minerals similar to those found on
earth's surface. One of the most important tools for recognizing these minerals is the
spectrum of sunlight reflected by them. At the visible and near-infrared light wavelengths
measured by the Imager for Mars Pathfinder (IMP), the most important coloring materials in
the martian surface are iron minerals. There are two broad classes of iron minerals.
Minerals which occur in igneous rocks (such as pyroxene) have a relatively flat spectrum
and they reflect only a small amount of light; they are said to have a low reflectance.
Ferric iron minerals, which occur as weathering products, reflect longer-wavelength light
and absorb short-wavelength light, hence their very red color. The relative brightnesses
of Martian surface materials in IMP's different wavelength filter is a powerful tool for
recognizing the iron minerals present. |
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The shapes of the spectra of surface
materials can easily be measured from multispectral images. Measures of surface spectral
properties can also be shown as false color overlain on an image to summarize spectral
variations near the lander at a glance. The top image showns the region southeast of the
lander in true color. In the bottom image of the same region, the strength of the kink in
the spectrum at visible wavelengths (related to the abundance and particle size of
weathered ferric iron minerals) is shown in false color. Blue rocks are the least
weathered, red soils are most weathered, and green soils and rock faces show an
intermediate state of weathering. The earliest survey of
spectral properties of the rocks and soils surrounding Pathfinder was acquired as a narrow
strip covereing the region just beond the where the rover made its egress from the lander.
The wavelength filters used, all in the binocular camera's right eye, cover mainly visible
wavelengths. These data reveal at least five kinds of rocks and soil in the immediate
vicinity of the lander. All of the spectra are ratioed to the mean spectrum of bright red
drift to highlight the differences. Different occurrences of drift (pink spectra) are
closely similar. Most of the rocks (black spectra) have a dark gray color, and are both
darker and less red than the drift, suggesting less weathering. Typical soils (green
spectra) are intermeidate in properties to the rocks and drift. Both these data and
subsequent higher resolution images show that the typical soil consists of a mixture of
drift and small dark gray particles resembling the rock. However two other kinds of
materials are significantly different from the rocks and drift. Pinkish or whitish pebbles
and crusts on some of the rocks (blue spectra) are brighter in blue light and darker in
near-infrared light than is the drift, and they lack the spectral characteristics closely
associated with iron minerals. Dark red soils in the lee of several rocks are about as red
as the drift, bust consistently darker. The curvature in the spectrum at visible
wavelengths suggests either more ferric iron minerals than in the drift or a larger
particle size. |
One of the more unusual rocks at the
site is Ginger, located southeast of the lander. Parts of it have the reddest color of any
material in view, whereas its rounded lobes are gray and relatively unweathered. These
color differences are brought out in the inset, enhaced at the upper right. In the false
color image at the lower right, the shape of the visible- wavelength spectrum (related to
the abundance of weathered ferric iron minerals) is indicated by the hue of the rocks.
Blue indicates relatively unweathered rocks. Typical soils and drift, which are heavily
weathered, are shown in green and flesh tones. The very red color in the creases in the
rock surface correspond to a crust of ferric minerals. The origin of the rock is
uncertain; the ferric crust may have grown underneath the rock, or it may cement pebbles
together into a conglomerate. Ginger will be a target of future super- resolution studies
to better constrain its origin. In this scene showing the
rover deployed at Yogi, the colors have similarly been enhanced to bring out differences.
The same three kinds of rocks are recognized as in the distance. Yogi (red arrow), one of
the large rocks with a weathered coating, exhibits a fresh face to the northeast,
resulting perhaps from eolian scouring or from fracturing off of pieces to expose a
fresher surface. Barnacle Bill and Cradle (blue arrows) are typical of the unweathered
smaller rocks. During its traverse to Yogi the rover stirred the soil and exposed material
from several cm in depth. During one of the turns to deploy the APXS (inset and white
arrow), the wheels dug particularly deeply and exposed white material. Spectra of this
white material show it is virtually identical to Scooby Doo, and such white material may
underly much of the site. |
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The Mars Pathfinder Magnetic Properties
Experiment primarily involves an array of permanent magnets on the lander. The magnets are
assembled to produce a bullseye pattern of attracted dust using an outer annular ring
magnet, 18mm in diameter, surrounding a central cylindrical magnet. In each of two magnet
arrays, five such magnets of progressively increasing strength, are mounted in magnesium
blocks.
These magnets are intended to attract any magnetic
particles in the windborne dust. The picture shows a magnet array on Sol 6 and on Sol 13.
Dust has clearly accumulated on the two strongest magnets. As more dust is attracted with
time, we expect the patterns on the magnets to become clearer. |
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One of the first "multispectral spots"
obtained by the IMP camera was of the Stripe Rock on Sol 4. A multispectral spot
measurement obtains small images of a region of interest in all geology filters with no
image compression. Stripe rock is of interest to Mars Pathfinder scientists because of a
bright vertical stripe that appears on the center of the rock face. It was thought that
this stripe might be an intruded vein of material of different composition than the
surrounding rock. The color image of this rock shows that
the stripe is of similar color to the surrounding soils (see arrow). A detailed
examination of the rock was conducted to extract preliminary reflectance spectra (that is,
the variation of brightness with color) from nearby bright and dark soils, the stripe, and
the surrounding rock. Although these data require further calibration (e.g., the lower
reflectance at 965 nm is not reliable at this time), they do show that the general
spectral characteristic of the stripe is quite similar to the nearby dark soil. This
suggests that the "stripe" is actually an accumulation of soil deposited in a
crack in the rock face.
Mars Pathfinder Mission
Mineralogy and Geochemistry Science Operations Group |
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Barnacle Bill Rock
Hypothesis: APXS data show composition of rock is consistent with volcanic andesite,
but rough texture of surface suggests it may be a "breccia."
Could it be composed of many different rock fragments that combine to give a similar
overall composition?
Method: Target Barnacle Bill with "multispectral spot" (all geology
filters at full spatial resolution of about 1-2 cm per picture element)
Goal: Determine variability of reflectance spectra (mineralogy) across the face of
the rock
If all spectra are similar: rock is "homogeneous" (composed of the same
material)
If spectra vary: rock may be "heterogeneous" (such as an impact melt breccia
or sedimentary conglomerate)
Result: Spectra taken from many different locations show only two basic kinds of
spectra:
- Soil-like deposits
- Dark rock face
Implication: At spatial resolution of 1-2 cm, rock composition is homogeneous.
However, rock may be composed of fine-grained materials (< 1-2 cm) that cannot be seen
with this method. |
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This image shows the
location of Barnacle Bill rock (left of the Sojourner rover) and the approximate location
of the full-resolution "multispectral spot" acquired on Barnacle Bill. Lossless
(no compression) images were taken in all geology filters using the IMP camera to study in
detail the variation of brightness in each filter, which provides information regarding
the mineralogy of the material sampled. Spectra were extracted from several study regions
(shown to the right of the high resolution view). The green area represents soil found
behind the rock. Red patches represent brighter areas on the rock that are interpreted as
accumulations of wind-blown dust found in small holes, or vesicles, on the rock. Blue
patches represent darker rock faces not contaminated by a soil deposit. The spectra of
these materials are shown in the accompanying figure. |
Preliminary data acquired from the
"multispectral spot" image sequence for Barnacle Bill rock. Images were acquired
with no compression in all geology filters. Reflectance spectra (that is, the variation of
brightness with wavelength, or color) are shown for background soil (green), soil-like
deposits found on and within small holes in the rock (red), and dark portions of the rock
face (blue). Comparison of the spectra of these three types of materials demonstrates that
the rock has relatively homogeneous composition at the spatial resolution of the patches
sampled (about 1-3 cm). That is, all soil-like deposit and rock face spectra cluster in
both their overall brightness (reflectance) and shape of their reflectance curves. A more
heterogeneous rock would show variable spectral characteristics across its face. Note that
the spectra of the soil-like deposit is intermediate to that of the background soil and
rock face spectra. This is consistent with the interpretation that the soil-like deposit
is a relatively thin layer in which portions of the rock are also sampled within the
patches selected. Also shown are laboratory spectra of
oxidized and unoxidized volcanic rocks from Earth. Scientists will compare spectra of
terrestrial materials such as these to help determine the composition of the rocks
observed at the landing site in combination with data returned by other instruments such
as the APXS. |
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In the foreground of each image is "Flat
Top". Each frame was taken by the IMP camera using a different color filter. The
color filters alter the appearance of the image. The red filter has enhanced both the
textures of the rocks and the dust on the surface of "Flat Top". |
The Sojourner rover has successfully navigated the rear
deployment ramp. This high resolution color image shows the front, left portion of the
rover. The micron scale soil beneath the rover was the first specimen examined by the
Alpha Proton X-Ray Spectrometer. |
This image shows the Sojourner rover in its traveling
configuration. The rover has since stood up and driven onto the surface of Mars. The red
rectangle represents the location of the spectral analysis performed by the Imager for
Mars Pathfinder. |
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