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Mars Pathfinder Mission Status
July 31, 1997
4:30 p.m. Pacific Daylight Time
The Mars Pathfinder flight team has completed all of its science and engineering goals, four days before the primary mission draws to a close, said Dr. Matthew Golombek, Pathfinder project scientist, at today's press briefing.

Atmospheric-surface interactions were the focus of today's presentation. To set the stage, Dr. Mark Lemmon, a member of the Imager for Mars Pathfinder (IMP) camera team from the University of Arizona, presented new images of the Martian sunrise and sunset. True to color, the dawn images revealed pale pink sunrises and clouds floating overhead. The reddish tint is the result of Martian dust, composed of oxidized iron, which is present in the atmosphere. The sunset images -- color-enhanced to bring out structural detail in the atmosphere -- showed a sky darkening to salmon-colored hues.

These spectacular images of the Martian summer are possible by return of an unprecedented amount of science and engineering data -- on the order of 400 megabits just in the last nine days - - Golombek pointed out.

Temperature highs and lows at the landing site have not varied much, said Dr. Robert Haberle, a participating scientist from the NASA Ames Research Center. They range from highs of about minus 12 degrees Celsius (8 degrees Fahrenheit) to lows near minus 76 Celsius (minus 105 Fahrenheit). Frozen water-ice clouds are evident in the Martian sky during the early morning hours, but evaporate once temperatures rise. "We expect late night and early morning clouds, but we expect those clouds will burn off fairly rapidly with sunrise, giving way to a dusty Martian day," Haberle said. Although there has not been much variation in these weather conditions since Pathfinder arrived, they are expected to begin changing in about a month, as fall arrives and ushers in the dust storm season.

Atmospheric pressures, on the other hand, are fluctuating dramatically, sometimes peaking two, three or four times a day, Haberle noted. Pressure oscillations are indicative of a global scale thermal tidal system that is moving dust, water-ice or vapor clouds and other volatiles through the atmosphere. On Mars, these atmospheric variations are sizable, whereas on Earth they almost never occur.

Since data-gathering began, the maximum change in pressure over the course of a day has been 0.3 millibars, which is about 4.5 percent of the average pressure on Mars. On Earth, pressures that low might occur during a severe hurricane. A better understanding of these pronounced pressure oscillations will help scientists understand the processes by which volatiles enter and escape the Martian atmosphere, and may shed more light on the rise of regional and global dust storms.

Wind speeds have been increasing with altitude, reported Dr. Robert Sullivan of Arizona State University. And temperatures will vary dramatically with elevation. When ground temperatures are 16 to 21 degrees Celsius (60 to 70 degrees Fahrenheit), they can drop to minus 23 to 27 degrees Celsius (minus 10 to minus 15 degrees Fahrenheit) just five and a-half feet above the ground.

Images of the Martian landscape also revealed a shiny object about 1,200 meters (7/10ths of a mile) away from the lander. Dr. Michael Malin, a participating scientist, said the object is about the same dimensions and is probably the spacecraft's discarded backshell, which separated just before the spacecraft landed.

Although the Pathfinder lander and rover remain healthy, engineers plan to recharge the lander's battery during a two-day hiatus beginning Sunday, Aug. 3. The lander will perform some science experiments during the day, but will use most of its solar energy to charge the battery. At night, the craft essentially goes to sleep.

The rover will continue its daily traverses and spectrometer studies, rolling off to a smooth, dark region of soil called Mermaid Dune tomorrow. After taking measurements of the soil, scientists will identify one of three large, dust-free rocks -- Shark, Half Dome and Wedge -- as the next target for study.

On this Martian day, Sol 27, Earthrise occurred at 2:49 a.m. PDT and sunrise followed at 5:52 a.m. PDT. The Earth later set at 4:23 p.m. PDT and the sun set at 6:41 p.m. PDT.

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