Mars Pathfinder Preliminary Results

P. H. Smith (LPL/U. Ariz.)

Pathfinder plays a key role as the first of the Surveyor series and as the first Discovery project to complete its mission. On July 4 the Pathfinder lands at Ares Vallis chosen as a grab-bag sample of small rocks washed down from the highland regions by the ancient catastrophic floods that once inundated the region. A multi-spectral, stereoscopic camera (IMP) was selected with the capability to discriminate rock types according to their spectral signatures between 0.4 and 1.1 microns. This range gives information on the iron mineralogies (the weathering of ferrous to ferric minerals) and some compositional information with the 0.9 micron pyroxene band. Stereo rangefinding allows contour-mapping of the surface, calculation of rock sizes, and helps with rover guidance. Operationally the camera data determines which rocks seem spectrally interesting and the stereo images allow the rover team to station the APXS against the rock for a night-long integration. The resulting data constrains the elemental composition which is then combined with the spectral data to determine the mineralogy of the rock.

The study of the atmosphere is also a prime scientific goal. The ASI/MET team has instruments for measuring diurnal temperature and pressure variations as well as wind velocity. During the descent they also derive the vertical profiles of the atmosphere. IMP has three windsocks that are monitored hourly for wind signatures; looking at all three simultaneously gives the vertical wind gradient. IMP also has 8 atmospheric filters that allow the camera to image the sun directly and measure the opacity variations hourly throughout the day. At night, bright star and Phobos observations with the geology filters continue the characterization. Besides the dust opacity, three filters in the 0.94 micron water band are able to measure water vapor at large airmass factors. Finally, a series of magnets at various positions on the lander will show indications of the magnetic properties of windblown dust. This scientific station could last as long as an earth year on Mars; therefore, seasonal changes in the weather and surface can be tracked.