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Mars Pathfinder

Current Science Data
July 21, 1997

Current Science Data

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Shown here is a comparison of the APXS analysis of Yogi (A-7) and Barnacle Bill (A-3). Also shown are the Martian meteorites, Viking soils, and terrestrial ultramafic rocks and basalts. The two lines on the graph are Martian and terrestrial fractionation trends, respectively. Recent images suggest that the analysis of Yogi may have a significant soil component, and this rock analysis must be considered to be very preliminary.

Yogi and Barnacle Bill are more earthlike than we would have expected from consideration of the Martian meteorites. Yogi is a more primitive rock than Barnacle Bill, having not gone through as much "cooking" as Barnacle Bill.

Shown here is a scheme which classifies volcanic rocks on the basis of their alkalis (Na2O and K2O) and silica (SiO2) contents. The possibility that these rocks are not volcanic, but rather the result of an impact event, cannot be ignored. If Yogi (A-7) and Barnacle Bill (A-3) are volcanic, then Yogi is a basalt and Barnacle Bill is an andesite. Basalts are the most common rocks in our solar system, covering most of Mercury, Venus, Earth, our Moon, and Mars. Basalts are important rocks for deciphering the history of rocky bodies in the solar system, and the Pathfinder Martian basalts will undoubtedly lead to major revisions in our understanding of the red planet. Shown here are the three soil analyses labeled A-2, A-4, and A-5 compared to the average of soils analyzed by the Viking landers in 1976. The APXS (Alpha Proton Xray Spectrometer) analyses are preliminary, and the least amount of error is induced by normalizing to the major element silicon. As can be seen, the three Sojourner analyses are all quite similar to the Viking soils, even though the Viking landers were over a 1000 kilometers away from the Pathfinder landing site. This implies that there is a globally homogeneous soil layer on Mars, probably the result of many, many years of mixing by the winds of Mars. As a result, the Sojourner rover will mainly concentrate on analyzing rocks for the rest of the mission.

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Shown here are the analyses of Yogi (A-7) and Barnacle Bill (A-3) on a plot of Na/Si vs. Fe/Mn. Na/Si is not a good indicator of different planetary bodies (and the APXS analyses of Na have a large error), but the Fe/Mn ratio is a diagnostic feature that separates Martian rocks from all other rocks. As can be seen, Yogi and Barnacle Bill are quite Martian.

Shown here are three pie charts showing the normative mineralogy of Yogi and Barnacle Bill. A norm is a way of taking a chemical analysis and converting it into mineral phases. The two pie charts on the left are conventional CIPW normative plots of Yogi and Barnacle Bill. The main difference between these two rocks is in the normative quartz contents. Yogi has less normative quartz than Barnacle Bill, indicative of the primitive nature of Yogi. Yogi has not undergone the extensive "cooking" that Barnacle Bill has experienced.

On the right is the "Mars Norm" for Yogi. The Mars Norm is a calculation made by Dr. Amitabha Ghosh (University of Tennessee) which attempts to calculate the actual mineralogy of a Martian basalt. The Mars Norm has been tested and calibrated with the Martian meteorites, and may be a better indicator of the actual mineralogy of Yogi. Interestingly, the Mars Norm of Yogi is quite similar to the CIPW norm of Yogi (top left), pointing towards its more earth-like character.

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Where is Mars Pathfinder? (93K)

Material Adherence on the Rover
(Dust Settling Experiment) Preliminary Results!

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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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Volcanic Rock Classification

Igneous rocks are usually classified according to the minerals they contain. In the absence of mineralogic data, volcanic rocks can be classified using their chemical compositions. Using this system, Martian rock Barnacle Bill (labelled here as APXS site A-3) is classified as an andesite. The term "andesite" derives from the Andes Mountains in South America, where this type of lava is particularly abundant. Barnacle Bill's andesitic composition could indicate that it is a volcanic rock (a true andesite) or a physical mixture of particles of rocks such as granite and basalt. Such a mixture could have been formed as the particles were transported and deposited as a sediment, or could have been produced during a large impact that pulverized and mixed the target rocks in andesitic proportions.
Magnesium/Silicon versus Aluminum/Silicon

SNC meteorites are thought to be Martian samples, based primarily on the fact that they contain trapped gases that have the composition of the Martian atmosphere. All the known SNC meteorites, as well as Viking soils, lie well to the left of the trend for Earth rocks in this diagram. Weight ratios of elements tend to be more precise than absolute element abundances, so ratios are used to plot these preliminary APXS data. Martian rock Barnacle Bill (labelled as APXS site A-3), plots near the line defined by SNCs, perhaps providing support for the idea that SNC meteorites are actually derived from Mars.
Calcium/Silicon versus Iron/Silicon

These three elements are especially well suited for APXS analysis. The compositions of SNC meteorites, as well as Viking soils, have higher iron/silicon ratios than terrestrial rocks. The APXS soil analysis A-2 plots directly on top of Viking soils in this diagram. However, Barnacle Bill's composition (A-3) plots to the left, because of its high silicon content.

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stripe_3color.jpg (62K)

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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

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:

  1. Soil-like deposits
  2. 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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