The Red Planet Revisited

Two “detectives” from Earth have been sent to our next-door neighbor in the solar system, Mars. They were sent to answer some fundamental questions about the geologic past of the red planet as well as its present condition.

FROM the earliest times, Mars has fired the human imagination. Our ancestors sensed that there was something unusual about the bright, red heavenly body that moved across the night skies out of step with the rest of the stars. The ancient Babylonians, Greeks, and Romans named the planet after their gods of war and of death, unaware of the fact that its reddish color was merely evidence of a landscape covered with iron oxide dust.

In more recent times, as astronomers turned increasingly powerful telescopes to the solar system, they could not help but notice that our reddish neighbor has seasons, icy poles, and other features reminiscent of those of Earth. In the 20th century, the initial surveys of Mars were made by a number of space probes, or spacecraft, including orbiters and landers, sent by the Soviet Union and by the United States. Then came the Mars Pathfinder mission, which riveted the attention of millions of television viewers in July 1997.a

Presently, the Mars Global Surveyor orbiter is gathering data on the red planet. While these missions have provided a wealth of information, many fundamental questions regarding Mars still remain.

Where Is the Water?

A common element to these questions is water. Scientists speculate that in the distant past, Mars was very different from what they see today. They describe a planet that used to have a warmer climate, moist air, and running rivers lacing its surface. However, somehow the water vanished, leaving a dry, dusty, windswept orb that makes even Earth’s deserts seem lush. Where did the water go? Where can water presently be found on Mars, and in what form? How does water influence the weather and the climate of Mars?

“It’s a detective story,” says Norman Haynes, former head of the Mars Exploration office at NASA’s Jet Propulsion Laboratory, in Pasadena, California. “The real trick on Mars is to find out what happened to the water.” Scientists hope soon to move closer to an answer. About every two years, when Earth and Mars are favorably aligned, researchers plan to launch robotic probes to chisel away at the Martian mystery.

The latest pair of such “detectives”? A polar-orbiting weather watcher and an on-site robot chemist that will give scientists a better look at the Martian underground. Their names: Mars Climate Orbiter and Mars Polar Lander.

Going to Mars

The Mars Climate Orbiter was launched on December 11, 1998, from the Kennedy Space Center, at Cape Canaveral, Florida, and began its nine-month journey to Mars. It was designed to maintain a 250-mile [400 km]-high orbit, from which it was to monitor the planet’s atmosphere, surface features, and polar caps. Observations were to last a complete Martian year—that is, 687 Earth days.

On September 23—the day the climate orbiter was scheduled to start observing Mars—scientists at NASA’s Jet Propulsion Laboratory said that they had lost communication with the weather orbiter. “We believe the spacecraft came in at a lower altitude than we thought it would,” said Richard Cook, project manager of the mission. “That potentially resulted in the loss of the mission.” That mission was to monitor the seasonal changes on the surface of the planet and to provide researchers with important clues regarding the planet’s early climate history.

Scientists hope that not everything is lost. This is because the second spacecraft—the Mars Polar Lander—is on its way to Mars. It was launched on January 3, 1999, and is scheduled to arrive at Mars in early December of this year. Where should this lander touch down to yield maximum results?

Where to Land?

Remember, the water question is paramount in Mars exploration. Where is the ideal place on that planet to study water? Weather, climate, and the water cycle on Earth are studied by comparing the results of thousands of individual studies conducted using a wide variety of instruments in many different locations. Exploration of other planets, however, requires a much more selective process. Because each opportunity to study Mars from the surface is rare, scientific investigators must be careful when deciding what instruments to send and where to send them.

For the study of the Martian climate, the polar regions are ideal sites—albeit vastly different from the rock-strewn floodplain where Mars Pathfinder settled two years ago. The polar regions are where the seasonal extremes occur. It is thought that seasonal dust storms deposit a thin layer of dust in the polar regions. When winter comes, the dust is frozen beneath carbon dioxide and water ice. Over time, many layers have built up. “These layers preserve a record of [Mars’] climate history,” says Ralph Lorenz, of the University of Arizona. Experts believe that the exploration of this new territory will be a significant step in Mars research. How so? What will the lander do after it has landed?

Looking Beneath the Surface

A spiderlike machine standing three and a half feet [1 m] tall, the lander has three legs as well as a six-and-a-half-foot [2 m] robotic arm with a scoop at the end. Its mission will start before touching down on Martian soil. Just before reaching the atmosphere of the red planet, the lander will release a pair of pods, each about the size of a basketball.

These projectiles will free-fall to the surface and hit the ground at about 450 miles [700 km] per hour. The pods are designed to shatter on impact and release a pair of smaller probes that will be driven as deep as three feet [1 m] into the soil. Once buried, the probes will release tiny drills and begin testing the chemical makeup of the Martian soil. The first goal will be to trace any water that might lurk frozen underground.

Shortly after the probes reach the ground, the lander will follow, descending by parachute. Equipped with cameras and sensors, the lander is designed to study the terrain and weather of Mars. It will snap pictures both during its descent and after it has landed on the ground. The microphone it carries will record for the first time the sound of the Martian wind. The lander is scheduled to function for about 90 days after touchdown.

An Urge for Exploration

Of course, it will take scientists years to study and analyze the data collected during this mission, which is part of a 16-year effort to learn more about Mars. Besides NASA, the European, the Japanese, and the Russian space agencies are also involved in this endeavor. Ultimately, scientists hope that future missions will return Martian soil samples to Earth-based laboratories for analysis. These may help them finally answer the question of what happened to the climate of our red planetary neighbor, Mars.

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Did Life Come From Mars?

Meteorite ALH84001—which is believed to have come from Mars—was discovered in Antarctica in 1984. In August 1996 some researchers at NASA’s Johnson Space Center and at Stanford University announced that the potato-size rock contains evidence, but not clear proof, of life on Mars—organic compounds, mineral deposits, and fossilized microbes. The implication was that life on Earth may have originated on Mars.

However, just about everyone else in the scientific community now agrees that this meteorite cannot provide any solid evidence that life came from Mars. “I think it’s very unlikely they have remnants of biological activity,” said William Schopf, of the University of California, Los Angeles. Similarly, Ralph P. Harvey, of Case Western Reserve University, said: “Although life on Mars is an appealing concept to so many of us, ALH[84001] evidently contains scarce proof of it.”b

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Forty Years of Mars Exploration

◼ In 1960 the Soviet Union launched the first planetary probes, aimed at Mars. The probes did not reach orbit.

◼ On July 14, 1965, Mariner 4, from the United States, flew past Mars and transmitted photographs and measurements back to Earth.

◼ In 1971, Mars 3, a Soviet probe, dropped a capsule that made the first soft landing on Mars. Mariner 9, a U.S. probe, reached Mars that same year and photographed most of the planet’s surface. Mariner 9 also photographed the planet’s two small moons, Phobos and Deimos.

◼ Two U.S. probes, Viking 1 and Viking 2, landed on Mars in 1976. The probes operated for years, carrying out complex experiments.

◼ In 1988, Soviet scientists launched two spacecraft, Phobos 1 and Phobos 2, to Mars. Phobos 1 failed during the flight, but Phobos 2 reached Mars and sent back its findings for several days.

◼ In 1992 the United States launched the Mars Observer probe, which failed in its mission.

◼ The Mars Pathfinder, carrying the Sojourner rover, landed on Mars on July 4, 1997. Stunning color photos were sent back from the surface of the red planet.

[Pictures]

Mariner 4

One of the Viking landers

Phobos 2

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Mars Climate Orbiter

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Mars Polar Lander

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Panorama of Mars landscape, taken by Mars Pathfinder

[Picture Credit Lines on page 14]

Page 15: Meteorite: NASA photo; background: NASA/U.S. Geological Survey; orbiter and lander: NASA/JPL/Caltech

Pages 16 and 17: Landscape, Mariner 4, Viking lander: NASA/JPL/Caltech; planet: NASA photo; Phobos 2: NASA/National Space Science Data Center