Visions of Mars

Photograph by NASA/JPL/Malin Space Science Systems (MSSS) National Geographic Space Special

Mars, the fourth planet from the sun, has fascinated Earthlings throughout the ages. Nicknamed the red planet, Earth's flamboyantly hued next-door neighbor is often clearly visible in our nighttime sky, even though the two celestial bodies are more than 34 million miles apart at their closest points. Long before space exploration began, astronomers looked at Mars through telescopes and found that it appeared to share many characteristics of Earth, such as dust storms, clouds, and polar ice caps. Since it seemed the most Earthlike of the planets in our solar system, scientists and others speculated about life on Mars. Some even became convinced that intelligent beings existed there. But space probes sent to Mars in recent decades have quieted the conjecture. The NASA orbiters taking pictures from above and the robotic rovers exploring the surface have shown Mars to be far different from Earth and more like the moon—dusty, cratered, and barren.


Wilford, John Noble. Mars Beckons. Knopf, 1990.

Squyres, Steven W. "Mars." World Book at NASA.

Mysterious Mars

Mars's blood-red color and seemingly erratic path through the sky led the ancients to link it with war and chaos. Mythology sprang up around the red planet. The Babylonians named it Nergal for their god of the underworld. The Greeks identified it with their war god, Ares, and the Romans with theirs, Mars.

With the advent of the telescope, early astronomers began studying Mars in detail. In 1659 Dutch astronomer Christiaan Huygens sketched a curious dark region of Mars known today as Syrtis Major. Italian astronomer Giovanni Schiaparelli drew a detailed map of the planet in the late 19th century, naming regions and using the word canali to describe linear streaks he saw on the surface. "Channel" would have been a better translation of the Italian word, but the more phonetically similar "canal" captured the fancy of the public and of a Massachusetts business tycoon turned amateur astronomer named Percival Lowell. To Lowell, canals implied the presence of life—and an advanced civilization capable of building waterways.

The idea of life on Mars took on a life its own. Inspired by the possibilities, early science fiction writers like H. G. Wells depicted a brutal race of tentacled Martians bent on conquering the Earth after spying from afar this prize of a "warmer planet, green with vegetation and grey with water, with a cloudy atmosphere eloquent of fertility" in his classic The War of the Worlds (1898). Forty years later Orson Welles produced a radio play about a Martian invasion of New Jersey that sounded realistic enough to cause mass panic in the streets. Whether or not people bought into the existence of these alien warriors (or later, into astronomer and astrochemist Carl Sagan's fanciful conjecture of "polar bear-sized creatures" roaming the frigid Martian landscape), a lot of them did begin believing in the possibility of life on Mars.

"Mars Revealed: A New Look at Forces That Shape the Desert Planet." National Geographic map supplement (February 2001).

Wilford, John Noble. Mars Beckons. Knopf, 1990.

Achenbach, Joel. "Life Beyond Earth." National Geographic (January 2000), 24-49.

Wells, H. G. The War of the Worlds. Signet Classics, 2007.

Other Resources
Poundstone, William. Carl Sagan: A Life in the Cosmos. Henry Holt and Company, 1999.

Jordan, Michael. Dictionary of Gods and Goddesses. Facts on File, 2004.

McKenzie, Michael. Mythologies of the World. Checkmark Books, 2001.

Unlocking the Mysteries of Mars

On July 14, 1965, many fantasies were replaced by facts. That's the day a NASA space probe called Mariner 4 captured flyby images 6,118 miles above Mars's surface. Anxious scientists gathered around the transmitted images, but saw no canals, no liquid water, no crops. And to the great disappoint of some, no sign of life of any kind. Subsequent Mariner missions confirmed only a rock-strewn planet with huge geologic features, most of them apparently little changed in billions of years. The words of a NASA news release on September 11, 1969, were unmistakable: "Mariner 6 and 7" revealed Mars to be heavily cratered, bleak, cold, dry, nearly airless and generally hostile to any Earth-style life-forms."

The only way to be sure about the existence of life-forms—past or present, large or microscopic—is to get down and dirty. The first successful foray to Mars's soil happened in 1976, when the Viking 1 and 2 landers descended via retro-rockets to the surface. Controlled remotely from Earth, each lander's robotic arm scooped soil samples for testing, mixing the flourlike dust with water and chemicals in a search for indications of life. None were found.

Other landers have followed. Today, two rovers— Spirit and Opportunity —are exploring the planet. In more than four years of solar-powered travel, the twin rovers have transmitted spectacular close-up images of the red planet's terrain, and they’ve done on-the-spot analysis of soil and rocks. Overhead, three orbiters circle the planet, feeding computers at the University of Arizona with vivid images of the surface. Photo collages made from thousands of images chart nearly the entire planet.

Still, we barely know our celestial neighbor, especially when it comes to the big question about life. "Mars was a habitable world at some point early in its history," says Jim Bell, a planetary scientist at Cornell University. "We don't know exactly when, and we don’t know precisely where. Future missions will have to figure that out."

Petit, Charles W. "Making a Splash on Mars." National Geographic (July 2005), 58-77.

Wilford, John Noble. Mars Beckons. Knopf, 1990.

Other Resources
National Aeronautics and Space Administration.

HiRISE: High Resolution Imaging Science Experiment.

Sheehan, William. The Planet Mars: A History of Observation and Discovery. University of Arizona Press, 1996.

Mars Exploration Rover.

Mars Odyssey.

Mars Reconnaissance Orbiter.

Markley, Robert. Dying Planet. Duke University Press, 2005.

Other National Geographic Resources
Morton, Oliver. "Mars: Planet Ice." National Geographic (January 2004), 4-31.

Sawyer, Kathy. "A Mars Never Dreamed Of." National Geographic (February 2001), 30-51.

Newcott, William R. "Return to Mars." National Geographic (August 1998), 4-29.

Raeburn, Paul. Uncovering the Secrets of the Red Planet. National Geographic Society, 1998.

Mars Statistics

Radius at equator: 2,110 miles (about half of Earth’s radius)

Temperature: Ranges from minus 195 degrees Fahrenheit at the poles in winter to 70 degrees Fahrenheit at the equator at midday

Gravitational force: 38 percent of Earth's (a person standing on Mars would feel only a little more than a third of his or her weight)

Distance from Earth: 34,600,000 to 249,400,000 miles

Length of day: 24 hours, 39 minutes, 35 seconds

Length of year: 687 Earth days


Squyres, Steven W. "Mars." World Book at NASA.

"Mars Fact Sheet." NASA.

Last updated: September 17, 2008