PASADENA, Calif. If all goes well, Friday will mark the latest chapter in NASAs ongoing campaign to explore Mars when the Polar Lander and two companion microprobes set down on the red planet.
The U.S. space agency hopes to chalk up its fourth spacecraft landing at Mars, a feat it first accomplished with the twin Viking missions in 1976 and again with Pathfinder in 1997. (In 1971, the Soviets became the first to land on Mars.)
The missions are the second installment in NASAs ambitious Mars Surveyor Program to send robotic spacecraft, both orbiters and landers, to the planet every 26 months. Mars Global Surveyor, which is now orbiting Mars, became the first spacecraft in the program when it was launched in 1996.
(The Mars Climate Orbiter, a weather-studying and communications satellite that was one half of the $328-million Mars Surveyor 98 program was lost Sept. 23 as it entered orbit.)
The NASA program is slated to continue to bat spacecraft at Mars at a staccato clip well into the next decade, with missions already scheduled for 2001, 03 and 05.
Although the Mars Polar Lander will not have a rover like Pathfinder's Sojourner, which quickly became the darling of that mission, the 1,270-pound (576-kilogram) spacecraft carries a handful of scientific instruments to help scientists unravel Mars climate history and its current water resources, thought by some to be fairly abundant.
Unlike Pathfinder, which bounced down with the aid of airbags, the Polar Lander is designed to make a powered descent to the surface of Mars after its 470-million-mile (757-million-kilometer) journey from Earth, riding on retro-rockets as did the Viking landers.
Alighting on three spindly legs at 3:14 p.m. ET on Friday, the lander should find itself in an area never before explored by other spacecraft: Mars south pole.
Scientists targeted the area because of the unique soils found there. Called polar layered terrain, the frosty, banded soils could contain a synopsis of Mars climatic history.
A robotic arm on the lander will dig into those layers, analyzing individual samples and imaging them at close range. By doing so, scientists hope to peel back Mars history one layer at a time.
Meanwhile, 60 miles (100 kilometers) away, the twin Deep Space 2 microprobes, named Scott and Amudsen, will also dig literally into the same soils, looking for evidence of water vapor. That mission will complete most of its work within hours of landing, while the much larger lander will extend its robotic arm about four days later.
The Polar Lander will jettison the $29-million set of probes as it enters the martian atmosphere, sending them hustling down on to the planet at speeds of up to 400 mph (640 kph). Upon landing, the 5.3-pound (2.4-kilogram) probes will separate into two, with a bullet-shaped aftbody on each slicing into the soil to sample it.
Like Pathfinder, the Mars Polar Lander could yield a feast of images of the red planet, including a movie made during its descent to its surface. The lander also carrieds a tiny microphone that should, for the first time ever, record the sounds of another planet.
The Polar Lander could last on the surface anywhere from 60 to 90 Martian days, called sols. The microprobes, which do not have solar arrays to generate their own power, are designed to last as long as three days.
Mars is the fourth planet from the sun. The planet has two moons and is about half the size of the Earth. Its atmosphere is cold and thin, made up mostly of carbon dioxide. Its topography is a study in extremes, with mountains as tall as 16 miles (26 kilometers) and valleys as large as the continental United States and five times as deep as the Grand Canyon.
However, scientists think Mars was a far different place in the past, with a warmer and wetter climate. Past photos of Mars show evidence of catastrophic flooding, although the planet's surface now is dry and dusty. The missions set to climax on Friday are aimed at shedding further light on the mystery of where Mars' water went.
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