Mars Pathfinder Science Objectives

The Mars Pathfinder project is one of the first NASA Discovery class missions. It will land a single vehicle with a microrover (Sojourner) and several instruments on the surface of Mars in 1997. Sojourner's mobility provides the capability of "ground truthing" a landing area over hundreds of square meters on Mars. Pathfinder will be investigating the surface of Mars with three additional science instruments (a stereoscopic imager with spectral filters on an extendible mast (IMP)), an Alpha Proton X-Ray Spectrometer (APXS), and an Atmospheric Structure Instrument/Meteorology package (ASI/MET). These insturments will allow investigations of the geology and surface morphology at sub-meter to a hundred meters scale, the geochemistry and petrology of soils and rocks, the magnetic and mechanical properties of the soil as well as the magnetic properties of the dust, a variety of atmospheric investigations and rotational and orbital dynamics of Mars. Landing downstream from the mouth of a giant catastrophic outflow channel (Ares Vallis) offers the potential for identifying and analyzing a wide variety of crustal materials, from the ancient heavily cratered terrains to intermediate-aged ridged plains to reworked channel deposits. Examination of the different surface materials will allow first-order scientific investigations of the early differentiation and evolution of the crust, the development of weathering products and the early environments and conditions that have existed on Mars.

Suface Morphology and Geology at Meter Scale

The Imager For Mars Pathfinder (IMP) will reveal martian geologic processes and surface-atmosphere interactions similar to what was observed at the viking landing sites. Observations of the general landscape, surface slopes and the distribution of rocks will be obtained by panoramic stereo images at various times of the day. Any changes in the scene over the lifetime of the mission might be attributed to the actions of frost, dust or sand deposition, erosion or other surface-atmosphere interactions. A basic understanding of the surface and near-surface soil properties will be obtained by the Rover and lander imaging of rover wheel tracks, holes dug by the rover wheels, and any surface disruptions caused by airbag bounces or retractions.

Petrology and Geochemistry of Surface Materials

The Alpha-Proton X-Ray Spectrometer (APXS) and the visible to near-infrared spectral filters on the imp will determine the dominant elements that make up the rocks and other surface materials of the landing site. A better understanding of these materials will address questions concerning the composition of the martian crust, as well as secondary weathering products (such as different types of soils). These investigations will provide a calibration point for orbital remote sensing observations such as Mars Global Surveyor. The IMP will be able to obtain full multi-spectral panoramas of the surface and underlying materials exposed by the rover and lander. since the APXS is mounted on the rover, it will be able to characterize rocks and soils in the vicinity of the lander.

Magnetic Properties and Soil Mechanics of the Surface

Magnetic targets are distributed at various points around the spacecraft. Multi-spectral images of these targets will be used to identify the magnetic minerals which make up airborne dust. In addition, APXS measurement taking of the material collected on the magnetic targets will determine the presence of titanium and iron in the dust. Using a combination of the images, and APXS measurements, it is possible that the mineral composition of the rocks can be inferred. Detailed examination of the wheel-track images will give a better understanding of the mechanics of the soil surrounding the landing site.

Atmospheric Structure as Well as Diurnal and Seasonal Meteorological Variations

The Atmospheric Structure Instrument/Meteorology (ASI/MET) experiment will be able to determine the temperature and density of the atmosphere during Entry, Descent and Landing (EDL). In addition, three-axis accelerometers will be used to measure atmospheric pressure during this period. Once on the surface, meteorological measurements such as pressure, temperature, wind speed and atmospheric opacity will be obtained on a daily basis. Thermocouples mounted on a meter-high mast will examine temperature profiles with height. wind direction and speed will be measured by a wind sensor mounted at the top of the mast, as well as three wind socks interspersed at different heights on the mast. Understanding this data is very important for identifying the forces which act on small particles carried by the wind. Regular sky and solar spectral observations using the IMP will monitor windborne particle size, particle shape, distribution with altitude and the abundance of water vapor.

Rotational and Orbital Dynamics of Mars

The Deep Space Network (DSN), by using two-way X-Band and doppler tracking of the Mars Pathfinder lander will be able to address a variety of orbital and rotational dynamics questions. Ranging involves sending a ranging code to the lander on mars and measuring the time required for the lander to echo the code back to the Earth-based station. dividing this time by the speed of light results in an accurate measurement (within 1-5 meters) of the distance from the station to the spacecraft. As the lander moves relative to the tracking station, the velocity between the spacecraft and Earth causes a shift in frequency (doppler shift). Measuring this frequency shift provides an accurate measurement of the distance from the station to the lander. Within a few months of observing these features, the Mars Pathfinder lander location can be determined within a few meters. Once the exact location of Pathfinder has been identified, the orientation and precession rate (regular motion of the pole with respect to the ecliptic) of the pole can be calculated and compared to measurements made with the Viking landers 20 years ago. Measurement of the precession rate allows direct calculation for the moment of inertia, which is in turn controlled by the density of the martian rock with depth. Measurements similar to these are used on earth to determine the makeup of the earth's interior.

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