Before people even knew what planets were, Mars was an alluring glow in the night sky.
As early as the 1500s B.C., Egyptians refer to Mars as "Horus of the Horizon," a god whom they depicted as a human with the head of a hawk. Ancient Romans saw the fiery red light in the heavens and named it after their mythical god of war.
Early astronomers saw channels and suggested a dying society had dug canals to irrigate water from the planet's poles. Modern scientists claim to have found signs of Martian life in meteorites. Endless books and movies have detailed the lives of "little green men."
Three rovers — one that may have crashed upon landing, another due to reach Mars late Saturday and a third due down on Jan. 25 — are poised to reignite a fascination that has persisted since the ancients first noted the planet's glow.
Harsh, But Habitable?
Why Mars? There are, after all, nine planets in our solar system. One reason may be the planet's similarity to our own home. A day on Mars is only 37 minutes longer than a day on Earth. The temperatures are harsh (ranging from -100 degrees Fahrenheit to 75 above), but may be at least bearable at some locations. The air is thin in oxygen (0.13 percent) and rich in carbon dioxide (95.3 percent). The air pressure is low at 7 millibars versus Earth's 1,000 millibars.
That may not sound all that habitable, but it is — compared to the competition. The air pressure on Venus, for example, would crush any visitor in seconds. And if the pressure didn't kill you, the searing temperatures would. The gaseous planets, Jupiter, Neptune, Uranus and Saturn, couldn't support you, Pluto is just a rock and Mercury is way too hot.
"There are only a couple, maybe a few places in the solar systems where people could conceivably go," explains Roger Launius, chair of space history at the Smithsonian National Air and Space Museum. "We've been to the moon and found out there's no life there. But there are a lot of questions remaining about Mars."
Italian astronomer Galileo Galilei was the first to turn his telescope on the planets, including Mars, in the 17th century. Decades later, Irish writer Jonathan Swift would foretell the discovery of two moons orbiting the planet in his book, Gulliver's Travels.
Lost in Translation
But much of the fascination surrounding Mars truly began churning just over a century ago when the Italian astronomer Giovanni Virginio Schiaparelli peered at the planet through his telescope and reported seeing "canali." In Italian, that means channels, but an American astronomy enthusiast, Percival Lowell, interpreted the word to mean canals — like the massive manmade Erie Canal project that had recently been completed.
Lowell traced the "canali" from his telescopes in Flagstaff, Ariz., and suggested that creatures on the planet had dug the canals to carry water from the polar caps to the middle of the planet. The idea of a struggling species fit with another theory, popular at the time, that the sun was slowly cooling, making planets further from the sun less and less habitable over the millennia.
"He was very well respected and he had this idea that what life existed on Mars was holding on by its fingernails," says Launius.
Lowell's theories quickly spread among the public and inspired science fiction writer H.G. Wells to write War of the Worlds. Taking his cue from Lowell, Wells envisions a dying Red Planet in the novel, with oceans that are drying up and resources that are thinning. To survive, the Martians invade Earth to rampage this planet's offerings.
Other writers soon followed suit with their own tales about Martians, including Edgar Rice Burroughs' A Princess of Mars and Ray Bradbury's The Martian Chronicles.
Following the Water
But as public imagination about the Red Planet grew, scientists were becoming more doubtful about the possibility of complex life on Mars as flyby spacecraft snapped images of a dry, desolate planet. Fantasies of a Mars civilization were quashed in 1976 when NASA got its first close-ups of the mysterious planet with the arrival of the Viking 1 orbiter and probe.
"That's when we knew for sure it was a rock-strewn place," says Launius." A lot of people were really disheartened."
Famed astronomer and thinker Carl Sagan was reportedly "never so depressed" in his life at the news. There was little hope now of finding any intelligent life on the planet, but the Viking probes did zero in on something the Italian astronomer had seen centuries ago — channels.
Could these gullies have been formed by ancient Martian rivers and oceans? Images from the Mars Global Surveyor and other craft have supported the idea and led to the new NASA motto: "Follow the Water."
If water exists or existed on Mars, many believe there could be evidence of past life or even primitive living creatures now on the planet. That idea was energized by the announcement in 1996 that astrobiologists had identified evidence of fossilized bacteria in a potato-sized Martian meteorite.
The theory has since come under severe scrutiny as other researchers analyze the meteorite, but the search for evidence of Martian life — in any form — has not died.
"Our expectations may have decreased over the past century," said Steven Dick, NASA's chief historian. "We're down from little green men to fossils from the past or bacteria just under the planet's surface. But that's still exciting."
As Mark Adler, the mission manager for NASA's Spirit probe, points out, there is much to learn about what lies on that mysterious red glow, more than 34 million miles away.
"Honestly," he says, "I have no idea what we'll see."