ARES VALLIS, MARS—Barnacle Bill, Yogi, Scooby Doo ... the week following the successful landing of Mars Pathfinder found the air waves and print media babbling about cartoon characters and "popping wheelies" on the Martian surface. The public was riveted. By July 9, the Pathfinder web sites had received over 265 million hits. And the Pathfinder team at the Jet Propulsion Laboratory (JPL) was tickled Martian pink.
Mars Pathfinder, in a bold demonstration of NASA's "faster, better, cheaper" mantra, landed safely at 19.33°N, 33.55°W, near the confluence of Ares and Tiu Valles, Mars, on July 4, 1997 (UT). Within 7 hours, the spacecraft began to transmit its first images.... Sure enough, it had landed in a catastrophic flood landscape. The team cheered as the first images came in and cheered again when they caught their first glimpse of "Twin Peaks," a kilometer-scale streamlined island (Figure 1). For Peter Smith, of the University of Arizona and Principal Investigator for the imager on the spacecraft, seeing this island was a dream come true. Smith had tried several times to get the team to shift the landing ellipse to ensure a mountainous view—luck gave it to him anyway.
Fig. 1. "Twin Peaks." This dual-peaked, streamlined island is located about 0.8 km southwest of the lander and provides scenic evidence for the catastrophic floods that once poured through the landing site region. Faint, horizontal markings on the right peak might be benches carved by the floods, lines of boulders stranded by the floods, or exposed bedrock layers.
The JPL microrover, Sojourner, was deployed on the second Martian day. It carries the alpha proton X-ray spectrometer (APXS) to determine the chemical composition of rock and "soil" at the landing site. During the first week on Mars, the APXS obtained data for a patch of wind-blown regolith and a cobble affectionately known as "Barnacle Bill" (Figure 2). The flood-deposit landing site was chosen in hopes that a variety of rock types would be available for the little Sojourner to examine.
Fig. 2. Sojourner was backed up against a rock named after cartoon character Yogi Bear when it snapped this pair of images showing the Mars Pathfinder lander (upper left) and Barnacle Bill rock (BB). Detailed textures can be seen in rocks at the foreground. The textures and patterns caused by the rover wheels (foreground) are used to help determine regolith properties such as particle size and density. The rim of a large impact crater is evident on the horizon behind the lander and "BB."
"Bill" astounded the geoscience community when the APXS results were presented on July 8 by investigators Rudy Reider and Harry ("Hap") Y. McSween, Jr. First, the rock appears to share a chemistry that has more in common with the SNC class of meteorites than with terrestrial or lunar rocks. SNC (shergottite, nakhlite, and chassignite) meteorites are thought to come from Mars—now it appears that Barnacle Bill (a rock that is undoubtedly from Mars) may help provide confirmation that, indeed, the SNC's and 'Bill' share the same parent body. Second, McSween interpreted the APXS results to indicate that the rock consists of about 1/3 quartz. The exact amount of quartz is still to be worked out, but, if confirmed, this will be the first discovery of Martian quartz. The lithology of Barnacle Bill remained somewhat elusive—McSween said that if it is a volcanic rock, it would be labeled an andesite and would indicate that martian magmas (molten rock in the subsurface) had become more evolved over time than had been previously thought. "Bill" could, however, be a sedimentary rock or impact melt or breccia. On July 9th, investigator Jeff Johnson explained that visible/near-infrared spectra suggest that Barnacle Bill has a homogenous composition at the 1–2-cm scale—further support for either a fine-grained volcanic or sedimentary rock.
It is mid-northern summer at the landing site, and temperatures during the first week ranged from highs up to 0°C down to -80°C at night. Winds were light, and the sky was pink. The atmospheric opacity is about the same as observed by the Viking 1 lander at the same time of year about 800 km away in the late 1970s. Evidence of previous wind action is evident all around the lander in the form of aeolian ripples, drifts, and scoured patches that expose underlying, bright-hued crusts. Geomorphologist Michael Malin interpreted the crusts as evaporites deposited by the drying flood waters. As the week drew to a close, attempts were being made to get an APXS spectrum of Yogi, a meter-scale boulder with an interesting surface texture. Next, APXS was expected to examine Scooby Doo, a rock that appears to be white. Prior to landing, there was much hope that white rocks would be found; the hope is that one such white rock will turn out to be a sedimentary carbonate, thus putting humanity a step closer to being able to address the the question of whether the planet ever harbored life.
Mars Pathfinder was funded in October 1993, along with the Near Earth Asteroid Rendezvous (NEAR) spacecraft, to be one of the first NASA Discovery-class missions. Under contract to the California Institute of Technology's JPL, the hardware was assembled, tested, and launched in a little more than 3 years. Mars Pathfinder was designated the "Sagan Memorial Station" on July 5, 1997, in honor and memory of the late astronomer, Carl Sagan.—Ken Edgett, Arizona State University, Tempe
Mars Pathfinder Special Issue, J. Geophys. Res ., 102 (E2), 3951–4230, 1997.
Mars Pathfinder Web Site: http://mpfwww.jpl.nasa.gov/
Back to Science for Everyone
