Alpha Particle X-ray Spectrometer Research Articles

Constraints on the composition and petrogenesis of the Martian crust

Spectral interpretation that silicic rocks are widespread on Mars implies that Earth's differentiated crust is not unique. Evaluation of observations bearing on the composition of the Martian crust (Martian meteorite petrology and a possible crustal assimilant, analysis of Mars Pathfinder rocks, composition of Martian fines, interpretation of spacecraft thermal emission spectra, and inferred crustal densities) indicates that the crust can be either basalt plus andesite or basalt plus weathering products. New calculated chemical compositions for Thermal Emission Spectrometer (TES) global surface units indicate that surface type 1 has basaltic andesite composition and surface type 2 has the composition of andesite. If these materials represent volcanic rocks, their calc‐alkaline compositions on a FeO*/MgO versus silica diagram suggest formation by hydrous melting and fractional crystallization. On Earth, this petrogenesis requires subduction, and it may suggest an early period of plate tectonics on Mars. However, anorogenic production of andesite might have been possible if the primitive Martian mantle was wet. Alternatively, chemical weathering diagrams suggest that surface type 2 materials could have formed by partial weathering of surface type 1 rocks, leading to depletion in soluble cations and mobility of silica. A weathered crust model is consistent with the occurrence of surface type 2 materials as sediments in a depocenter and with the alpha proton X‐ray spectrometer (APXS) analysis of excess oxygen suggesting weathering rinds on Pathfinder rocks. If surface type 1 materials are also weathered or mixed with weathered materials, this might eliminate the need for hydrous melting, consistent with a relatively dry Martian mantle without tectonics.

Athena Mars rover science investigation

Each Mars Exploration Rover carries an integrated suite of scientific instruments and tools called the Athena science payload. The primary objective of the Athena science investigation is to explore two sites on the Martian surface where water may once have been present, and to assess past environmental conditions at those sites and their suitability for life. The remote sensing portion of the payload uses a mast called the Pancam Mast Assembly (PMA) that provides pointing for two instruments: the Panoramic Camera (Pancam), and the Miniature Thermal Emission Spectrometer (Mini‐TES). Pancam provides high‐resolution, color, stereo imaging, while Mini‐TES provides spectral cubes at mid‐infrared wavelengths. For in‐situ study, a five degree‐of‐freedom arm called the Instrument Deployment Device (IDD) carries four more tools: a Microscopic Imager (MI) for close‐up imaging, an Alpha Particle X‐Ray Spectrometer (APXS) for elemental chemistry, a Mössbauer Spectrometer (MB) for the mineralogy of Fe‐bearing materials, and a Rock Abrasion Tool (RAT) for removing dusty and weathered surfaces and exposing fresh rock underneath. The payload also includes magnets that allow the instruments to study the composition of magnetic Martian materials. All of the Athena instruments have undergone extensive calibration, both individually and using a set of geologic reference materials that are being measured with all the instruments. Using a MER‐like rover and payload in a number of field settings, we have devised operations processes that will enable us to use the MER rovers to formulate and test scientific hypotheses concerning past environmental conditions and habitability at the landing sites.

Calibration of the Mars Pathfinder alpha proton X‐ray spectrometer

The chemical compositions of Martian rocks and soils examined with the alpha proton X‐ray spectrometer (APXS) during the Mars Pathfinder 1997 lander mission were not previously fully determined. Preliminary chemical results included major element abundances determined by the incomplete calibration of the X‐ray mode. The data collected from the alpha and proton detectors were not previously analyzed due to significant atmospheric contributions to the spectra. The backup instrument of the Pathfinder alpha proton X‐ray spectrometer flight instrument has been used to complete the instrument calibration under simulated Martian conditions at the University of Chicago. An APXS instrument has been used to create a Pathfinder calibration library to test the accuracy of all three instrument modes under simulated Martian conditions. This calibration library has been tested on a number of geologic standards. We have also corrected for instrument differences between the laboratory and flight units. Significant chemical results, somewhat different from those initially reported by Rieder et al. [1997a] and by Wänke et al. [2001], are reported by Foley et al. [2003] as a result of this reanalysis of the Pathfinder APXS data.

Final chemical results from the Mars Pathfinder alpha proton X‐ray spectrometer

The calibrated Pathfinder alpha proton X‐ray spectrometer (APXS) instrument is capable of measuring concentrations of all major and minor rock‐forming elements ranging from carbon through zirconium in atomic number. Therefore it is capable of constraining the petrology of the measured samples. In particular, the Pathfinder data are the first in situ measurements of Martian rocks and may be compared with previous remote‐sensing measurements as well as with the compositions of SNC meteorites. Pathfinder soil and rock sample abundances from the alpha, proton, and X‐ray modes have been quantified. The abundances suggest that (1) the rocks are covered with various amounts of soil; (2) the soil‐free rocks, on a volatile‐free basis, have some element ratios similar to Mars meteorites, yet have different bulk chemistry indicative of more evolved rocks with higher silica abundances; (3) the carbon and nitrogen contents are below detection limits; and (4) the alpha mode oxygen reveals excess amounts of oxygen in some samples, which is indicative of sample‐bound water (contained within minerals or glasses in samples).

The new Athena alpha particle X‐ray spectrometer for the Mars Exploration Rovers

The new alpha particle X‐ray spectrometer (APXS) is part of the Athena payload of the two Mars Exploration Rovers (MER). The APXS sensor head is attached to the turret of the instrument deployment device (IDD) of the rover. The APXS is a very light‐weight instrument for determining the major and minor elemental composition of Martian soils, rocks, and other geological materials at the MER landing sites. The sensor head has simply to be docked by the IDD on the surface of the selected sample. X‐ray radiation, excited by alpha particles and X rays of the radioactive sources, is recorded by a high‐resolution X‐ray detector. The X‐ray spectra show elements starting from sodium up to yttrium, depending on their concentrations. The backscattered alpha spectra, measured by a ring of detectors, provide additional data on carbon and oxygen. By means of a proper calibration, the elemental concentrations are derived. Together with data from the two other Athena instruments mounted on the IDD, the samples under investigation can be fully characterized. Key APXS objectives are the determination of the chemistry of crustal rocks and soils and the examination of water‐related deposits, sediments, or evaporates. Using the rock abrasion tool attached to the IDD, issues of weathering can be addressed by measuring natural and abraded surfaces of rocks.

Refined data of Alpha Proton X‐ray Spectrometer analyses of soils and rocks at the Mars Pathfinder site: Implications for surface chemistry

An extensive recalibration of the Alpha Proton X‐ray Spectrometer (APXS) was performed to improve the data evaluation of the Mars Pathfinder (MPF) rock and soil in situ measurements. Many samples and geostandards were measured with an MPF identical spare APXS under simulated Martian atmospheric pressure and low night temperature conditions. Precise calibration curves for major and minor elements were obtained. Using an improved spectral evaluation method for the original MPF spectra, refined and new elemental compositions of the MPF rocks and soils were derived. However, all initial conclusions about soils and rocks remained valid. The MPF soil composition revealed the mafic nature of the surface as inferred from the results of Viking 1 and 2 data. However, the MPF rocks reflect a felsic composition. For all samples, linear correlations of sulphur with all other elements were noticed, reflecting the fact that the rocks were covered with varying degrees of soil, which compared to the rocks is rich in sulphur. Extrapolating to low sulphur abundance (0.3%) the composition of a soil‐free rock was calculated. The MPF rock composition is high in Si and K and low in Mg and Fe compared to the soil. Using elemental data from MPF and Martian meteorites, a global estimation of the Martian crust composition was derived. The crust is of basaltic nature with a high abundance of incompatible elements (K, Rb, Nd, U, Th) and volatile elements (S, Cl), while carbonates are lower or absent.

Die Kosmochemie des Mars: Mit Raumsonden und Meteoriten

The chemical composition of Martian surface material is deduced using two different approaches: Direct measurements by the Alpha-Proton-X-Ray Spectrometer (APXS) flown to Mars by the Pathfinder mission, and by analyses of SNC meteorites, which are believed to be rocks from Mars. Several surface rocks of Mars measured by the APXS have different chemical compositions than those of SNC meteorites. Both compositions are also different from the Martian soil found at the Pathfinder landing site. However, this soil, which covers the surface of Mars, seems to be a mixture of local rocks, SNC meteoritic material, and an iron-rich component. From selected element correlations found in SNC meteorites and Martian surface samples, the bulk chemical composition of the planet is obtained. According to this model, Mars has an iron rich core of about 22 wt.%, which is relatively smaller than the Earth's core of about 33.5 %.

Characteristics of the Pathfinder APXS sites: Implications for the composition of Martian rocks and soils

An integrated study of spectral, elemental abundance, and image data from the Pathfinder alpha proton X‐ray spectrometer (APXS) measurement sites has led to a better understanding of the nature of Martian surface materials. This rigorous analysis provides a new level of detail that forms the basis for the results reported here and that can be used by future scientists trying to understand rocks and soils on Mars. Each APXS site has been precisely located by analyzing stereo Imager for Mars Pathfinder (IMP) and rover camera images to determine the position of the APXS during deployment. Rover and IMP images are used to assess local geology, namely, the presence of pebbles, clods, and aeolian features in soils and surface textures and dust concentrations on rocks. IMP spectra using the latest calibrations for radiance and reflectance are analyzed at a number of different illumination geometries for each APXS site. The three‐dimensional orientation of the sites has been determined and then used to compute the true sunlight (incidence) and viewing (emission) angles. Where suitable photometric coverage is available, reflectances are fit to the Hapke‐Irvine function. This is then used to adjust spectral reflectances to a normalized illumination geometry common to all rocks and soils. Comparing all the data sets shows a positive correlation among red/blue reflectance ratio, SO3 content, and dust abundance on rocks, indicating that rocks are coated with varying amounts of sulfur‐rich, red dust. Other elements, such as silicon and iron, are poor tracers for dust because their abundances within soil are similar to those within rock. Rock APXS targets that are bluer, poorer in sulfur, and have minimal dust coverage face toward the northeast, the direction in which winds may be capable of efficiently removing loose material under current Martian conditions. The IMP spectral properties of the soils show poor correlations with APXS elemental abundances. On the basis of currently released APXS data, bulk soils at the Pathfinder landing site are richer in silica and sulfur than the Viking landing sites, suggesting a different composition. The APXS soils with the most apparent pebbles are the poorest in SiO2, indicating that either the pebbles are more mafic than the APXS rocks or the pebble‐free soil component is inherently enriched in SiO2 compared to Viking soils. The mixture of materials at the APXS sites is a reflection of the overall complexity of Martian surface materials, a detailed understanding of which should drive the choice of future instruments and missions.

Chemical analyses of martian soil and rocks obtained by the Pathfinder Alpha Proton X-ray spectrometer

The US Mars Pathfinder spacecraft, which landed on the red planet on the 4th of July 1997, carried an Alpha Proton X-ray Spectrometer (APXS) that obtained the chemical composition of martian soil and rocks. The principles of the APXS operation are based on three interactions of alpha particles with matter: Rutherford alpha backscattering; (α, p) nuclear reactions; and X-ray generation by charged particles and X-ray excitation. The APXS, as was implemented on the Pathfinder mission, uses for all three modes of operation a monoenergetic beam of alpha particles from about 40 mCi of 244Cm radioisotope. It employs Si charged particle detectors for alpha and proton modes and a specially designed silicon PIN detector for its X-ray mode that does not require cooling for its operation. The APXS can detect all of the elements (except H and He) present above a few tenths of a percent for all major elements and several hundred ppm for many minor and trace elements. The APXS on Pathfinder was transported to various locations on the martian surface by the Sojourner rover which enabled it to analyze multiple soil and rock samples selected by the science team from the lander camera images. The APXS performed excellently under the adverse martian environment conditions and provided important information about the chemical composition of the martian soil and rocks. All of the analyzed rocks at the Pathfinder site were found to have high concentrations of silica, sulfur and iron, and low in magnesium, similar to those of the terrestrial basaltic andesites and definitely different from the SNC meteorites that are believed to have originated from Mars. All of the soil samples analyzed by the APXS have similar composition and are very close to the soil analyses obtained by the two Viking missions. The information derived from the Pathfinder APXS has significant implications about the origin and evolution of planet Mars.

Mineralogic and compositional properties of Martian soil and dust: Results from Mars Pathfinder

Mars Pathfinder obtained multispectral, elemental, magnetic, and physical measurements of soil and dust at the Sagan Memorial Station during the course of its 83 sol mission. We describe initial results from these measurements, concentrating on multispectral and elemental data, and use these data, along with previous Viking, SNC meteorite, and telescopic results, to help constrain the origin and evolution of Martian soil and dust. We find that soils and dust can be divided into at least eight distinct spectral units, based on parameterization of Imager for Mars Pathfinder (IMP) 400 to 1000 nm multispectral images. The most distinctive spectral parameters for soils and dust are the reflectivity in the red, the red/blue reflectivity ratio, the near‐IR spectral slope, and the strength of the 800 to 1000 nm absorption feature. Most of the Pathfinder spectra are consistent with the presence of poorly crystalline or nanophase ferric oxide(s), sometimes mixed with small but varying degrees of well‐crystalline ferric and ferrous phases. Darker soil units appear to be coarser‐grained, compacted, and/or mixed with a larger amount of dark ferrous materials relative to bright soils. Nanophase goethite, akaganeite, schwertmannite, and maghemite are leading candidates for the origin of the absorption centered near 900 nm in IMP spectra. The ferrous component in the soil cannot be well‐constrained based on IMP data. Alpha proton X‐ray spectrometer (APXS) measurements of six soil units show little variability within the landing site and show remarkable overall similarity to the average Viking‐derived soil elemental composition. Differences exist between Viking and Pathfinder soils, however, including significantly higher S and Cl abundances and lower Si abundances in Viking soils and the lack of a correlation between Ti and Fe in Pathfinder soils. No significant linear correlations were observed between IMP spectral properties and APXS elemental chemistry. Attempts at constraining the mineralogy of soils and dust using normative calculations involving mixtures of smectites and silicate and oxide minerals did not yield physically acceptable solutions. We attempted to use the Pathfinder results to constrain a number of putative soil and dust formation scenarios, including palagonitization and acid‐fog weathering. While the Pathfinder soils cannot be chemically linked to the Pathfinder rocks by palagonitization, this study and McSween et al. [1999] suggest that palagonitic alteration of a Martian basaltic rock, plus mixture with a minor component of locally derived andesitic rock fragments, could be consistent with the observed soil APXS and IMP properties.

The MUSES-C, mission description and its status

The MUSES-C mission is the world's first sample and return attempt to/from the near Earth asteroid Nereus (4660). It is the ISAS (The Institute of Space and Astronautical Science, Ministry of Education) which manages the mission that started in 1996 scheduling to be launched in January of 2002. The mission is built as a kind of technology demonstration, however, it is aiming at not only the in-situ observation but also the touch-down sampling of the surface fragments. The sample collected is returned to the Earth in January of 2006. The mission is a four year journey. The major purpose of it originally consists of the following four subjects: 1) The Ion thruster propulsion performed in interplanetary field as a primary means, 2) Autonomous guidance, navigation and control during the rendezvous and touch down phase, 3) The sample collection mechanism and 4) The hyperbolic reentry capsule with the asteroid sample contained inside it. The current primary objective is extended to carry the joint small rover with NASA/JPL, which is supposed to be placed on the surface and to look into the crater created by the sampling shot of the projectile. The rover is designated as the Small Science Vehicle (SSV) that weighs about 1 kg carrying three kinds of in-situ instruments: 1) A Visible Camera, 2) Near Infra-Red Spectrometer and potentially 3) Alpha-Proton X-ray Spectrometer (APXS) similar to that delivered on the Mars Path Finder. During the fiscal 1998, the spacecraft undergoes the PM tests and the FM fabrication starts from next year, 1999. The paper presents the latest mission description around the asteroid and shows the current status of the spacecraft as well as the instruments and so on. The mission will be the good example of an international collaboration in the small interplanetary exploration.

The chemical composition of Martian soil and rocks returned by the mobile alpha proton X-ray spectrometer: preliminary results from the X-ray mode.

The alpha proton x-ray spectrometer (APXS) on board the rover of the Mars Pathfinder mission measured the chemical composition of six soils and five rocks at the Ares Vallis landing site. The soil analyses show similarity to those determined by the Viking missions. The analyzed rocks were partially covered by dust but otherwise compositionally similar to each other. They are unexpectedly high in silica and potassium, but low in magnesium compared to martian soils and martian meteorites. The analyzed rocks are similar in composition to terrestrial andesites and close to the mean composition of Earth's crust. Addition of a mafic component and reaction products of volcanic gases to the local rock material is necessary to explain the soil composition.

The mission and operation of the mars pathfinder microrover

The Microrover Flight Experiment (MFEX) is a NASA OACT (Office of Advanced Concepts and Technology) flight experiment which is planned to be delivered and integrated with the Mars Pathfinder (MPF) lander and spacecraft system for landing on Mars on July 4, 1997. After landing, the MFEX rover will be deployed from the lander and begin a nominal 7 sol (1 sol = 1 Martian day ≈ 24 hours, 40 min.) mission to conduct a series of technology experiments, deploy an alpha proton x-ray spectrometer (APXS) on rocks and soil, and image the lander. This mission will be conducted under the constraints of a once-per-sol opportunity for command and telemetry transmissions between the lander and earth operators. As such, the MFEX rover must be capable of carrying out its mission under supervised autonomous control, in which, for example, goal locations are commanded and the rover navigates and safely traverses to these locations. In this paper, the mission of the MFEX is described, along with the on-board and ground-based systems which provide the capability for operating the vehicle.

Determination of the chemical composition of Martian soil and rocks: The alpha proton X ray spectrometer

The alpha proton X ray spectrometer (APXS) for the Mars Pathfinder mission is designed to provide a complete and detailed analysis of chemical elements in Martian soil and rocks near the landing site. The APXS instrument is carried on the Pathfinder Microrover, which will provide transportation to places of interest on the Martian surface. It consists of a complex sensor head, mounted on a simple but sophisticated APXS deployment mechanism (ADM) outside the warm electronics box (WEB) of the Microrover, and the instrument electronics, mounted inside the WEB. The ADM permits the instrument sensor head to be placed against soil and rock samples in arbitrary positions, ranging from horizontal to vertical, in order to perform in situ analysis. The possibility to transport the APXS to an arbitrary location, preselected on Earth, and to perform in situ analysis there, constitutes one of the most exciting aspects of the Pathfinder mission. The principle of the APXS technique is based on three interactions of alpha particles from a radioisotope source with matter: simple Rutherford backscattering, production of protons from (α, p) reactions on light elements, and generation of characteristic X rays upon recombination of atomic shell vacancies created by a bombardment. Measurement of the intensities and energy distributions of these three components yields information on the abundance of chemical elements in the sample. In terms of sensitivity and selectivity, data are partly redundant and partly complementary: alpha backscattering is superior for light elements (C, O), while proton emission is mainly sensitive to Na, Mg, Al, Si, S, and X ray emission is more sensitive to heavier elements (Na to Fe and beyond). A combination of all three measurements enables determination of all elements (with the exception of H and He) present at concentration levels above typically a fraction of 1%.

Mars Pathfinder project progress report

Mars Pathfinder, designed and built at the Jet Propulsion Laboratory/California Institute of Technology under contract to NASA's Office of Space Science, is the second of NASA's “cheaper, better, faster” Discovery missions; the first, the Near Earth Asteroid Rendezvous mission, was launched February 17, 1996 to tag up with Eros in February 1999. Launching on December 2, 1996 and landing on Mars on July 4, 1997, Pathfinder will demonstrate a low-cost delivery system to the surface of Mars. Historically, spacecraft that orbit or land on a distant body carry a massive amount of fuel for braking at the planet. Pathfinder requires fuel only to navigate to Mars; the spacecraft aerobrakes into the Mars atmosphere directly from Earth-Mars transfer trajectory, deploys a parachute at 10 km above the surface and, within 100 m of the surface, fires solid rockets for final braking prior to deployment of airbags that cushion touchdown. After landing, petals open to upright the lander, followed by deployment of a small rover and several science instruments.A major objective of Pathfinder—acquisition and return of engineering data on entry, descent, and landing (EDL) and lander performance—will be completed within the first few hours after landing. In addition, the lander will transmit images of the Martian surface the first day. Next, a rover will be deployed, as early as the first day, to perform mobility tests, image its surroundings, including the lander, and place an alpha proton x-ray spectrometer (APXS) against a rock or soil to make elemental composition measurements. The primary mission durations for the rover and lander are one week and one month, respectively. However, there is nothing to preclude longer operations up to a year.Pathfinder will also accomplish a focused, exciting set of science investigations with a stereo, multi-color lander imager on a pop-up mast; atmospheric instrumentation for measuring a pressure, temperature and density profile during entry and descent and for monitoring martian weather after landing; and the rover with its forward and aft cameras and the APXS. The APXS and the visible to near infrared filters on the lander imaging system will determine the elemental composition and constrain the mineralogy of rocks and other surface materials, which can be used to address first order questions concerning the composition of the crust, its differentiation and the development of weathering products. Regular tracking of the lander will allow determination of the martian pole of rotation, its precession since Viking era measurements, and the moment of inertia, which should allow discrimination between interior models that include a metallic core and those that do not.The Pathfinder Landing Site selected is Ares Vallis (19.5 °N, 32.8 °W), which is near the sub-solar latitude (15 °N) for maximum solar power at landing on July 4, 1997 and is at 2 km below the datum for correct operation of the parachute. The site is in Chryse Planitia a lowland where a number of catastrophic floods from the highlands to the north debouch. It is a “grab bag” site with the potential for sampling a wide variety of different martian crustal materials, such as ancient crustal materials, intermediate age ridged plains and a variety of reworked channel materials. Even though the exact provenance of the samples would not be known, data from subsequent orbital remote sensing missions could be used to infer the provenance for the “ground truth” samples studied by Pathfinder. Available data suggest the site is about as rocky as the Viking sites, but perhaps a bit less dusty. This site has streamlined islands nearby, carved by the flood, and a very smooth depositional surface at Viking resolution, except for small hills and secondary craters.This paper reports on the status of Mars Pathfinder's drive to space qualify its Flight System for launch on December 2, 1996 under a cost cap—in particular how the Project is dealing with qualification of its entry, descent and landing event and the surface operations phase as well as the normal launch and space flight phases. It also reports on its landing site selection and science plan.

The Mission and Operation of the Mars Pathfinder Microrover

The Microrover Flight Experiment (MFEX) is a NASA OACT flight experiment which is planned to be delivered and integrated with the Mars Pathfinder (MFP) lander and spacecraft system for landing on Mars on July 4, 1997. After landing, the MFEX rover is deployed from the lander and begins a nominal 7 sol (1 sol = 1 Martian day) mission to conduct a series of technology experiments, deploy an alpha proton x-ray spectrometer (APXS) on rocks and soil, and image the lander. This mission is conducted under the constraints of a once-per-sol opportunity for command and telemetry transmissions between the lander and earth operators. As such, the MFEX rover must be capable of carrying out its mission in a form of supervised autonomous control, in which, for example, goal locations are commanded and the rover navigates and safely traverse to these locations. In this paper, the mission of the MFEX is described along with the on-board and ground based systems which provide the capability for operating the vehicle.

Low cost approach to Mars Pathfinder

Mars Pathfinder, launching in December '96 and landing in July '97, will demo a low cost delivery system to the surface of Mars. Historically, spacecraft that orbit or land on a distant body carry a large amount of fuel for braking. Mars Pathfinder, thrusting only for navigation, enters directly into the Martian atmosphere, aerobrakes with its aeroshell, deploys a parachute at 10 km above the surface and, within 100 m off the surface, ignites solid rockets for final braking prior to deployment of air bags which cushion touchdown. After landing, petals open to upright the lander, exposing solar panels to the sun. Even though the lander and rover are expected to last longer, the major objectives of Mars Pathfinder, demonstrating EDL (Entry, Descent, Landing) and lander-rover surface operations, will occur within the first few days, at which time panoramic images of the surface will be transmitted and the rover will be deployed to conduct both mobility tests and rock composition measurements. While Mars Pathfinder is primarily an engineering demo, it accomplishes a focused, exciting set of science investigations with a stereo, multi-color lander imager; atmospheric instrumentation, used as a weather station after landing; and the rover with cameras and the APXS (Alpha Proton X-ray Spectrometer). This paper features Mars Pathfinder's approach to innovative and cost effective mission accomplishment, under a development cost cap. Mars Pathfinder is pathfinding a new way of doing business at NASA and JPL for small, low cost, Discovery class missions.

Mars Pathfinder Microrover

When the Mars Pathfinder (MPF) spacecraft lands on Mars, the Microrover Flight Experiment (MFEX) will be deployed and perform its mission to conduct technology experiments verifying the engineering design, to deploy an alpha proton x-ray spectrometer (APXS) to measure elemental properties of rocks and soil, and to image the MPF lander. In accomplishing this mission the MFEX rover must determine a safe path to goal locations traversing over a poorly known Martian surface. The rover does this mission with a capable mobile platform executing on-board autonomous functions of navigation and hazard avoidance. In this paper we describe the rover, its operational environment and the implementation of the on-board autonomous functions.