Mars has inspired the human imagination for more than a century, generating a parade of little green men and bug-eyed monsters first sparked by the belief that the planet was crisscrossed with alien-made canals.
Today, fantasy has given way to science, with the Spirit rover sending back eerily clear pictures of empty vistas and a president promising that humans will be sent to the Red Planet.
"We do not know where this journey will end. Yet we know this: Human beings are headed into the cosmos," President George W. Bush said.
Mars, in particular, has long been calling us.
The late astronomer Carl Sagan called Mars "a kind of mythic arena onto which we have projected our earthly hopes and fears."
"Why so many eager speculations and ardent fantasies about Martians, rather than, say, Saturnians or Plutonians?" Sagan wrote.
For starters, the fourth planet from the sun is not only Earth's neighbor, it's also the planet that most resembles our world. It has a roughly 24-hour day. It has weather, seasons, volcanoes and canyons.
When conditions are right, it is one of the brightest objects in the night sky.
Interest in Mars dates back at least to the Babylonians. The ancient Greeks named Mars for their god of war. Galileo was the first to see it through a telescope, in 1609.
But the past century's fascination with Mars can largely be traced to one vigorously promoted error: the mistaken discovery of canals supposedly constructed by intelligent beings.
Italian astronomer Giovanni Schiaparelli reported in 1877 that he had spotted some sort of channels -- possibly artificial waterways.
Mathematician and amateur astronomer Percival Lowell ran wild with the idea.
Lowell, founder of the Lowell Observatory in Flagstaff, Arizona, spent 15 years around the turn of the 20th century peering through his state-of-the art telescope at a hazy red dot with green splotches and white caps at the poles.
"He looks at it night after night, week after week, as long as he can, and he begins to see little straight lines, and they connect the green splotches to the poles," said Tom Burns, director of Ohio Wesleyan University's Perkins Observatory.
"He realizes that what he's seeing is without a doubt the most magnificent public works project our solar system has ever known," he said.
Lowell described Mars as a cold, desert-like planet whose desperate citizens had built hundreds of canals to carry water from melting polar ice caps to farmland.
"People wanted to see things on Mars. They wanted an inhabited planet," said associate professor Laurence Davies, who teaches on Mars at Dartmouth College.
Critics noted that, to be visible from Earth, the canals would have to be hundreds of kilometers wide. But Lowell's misguided theories sparked the popular imagination.
That led to speculation about what Martians might look like -- large eyes, spindly bodies and other alien stereotypes that still show up in today's science fiction.
In 1898, H.G. Wells began his novel The War of the Worlds with the proposition that for years Earth had been "watched keenly and closely by intelligences greater than man's" -- huge-headed Martians with whiplike tentacles. Edgar Rice Burroughs, the creator of Tarzan, wrote 11 Mars novels.
Radio listeners fled their homes in terror during Orson Welles' famously realistic Halloween 1938 broadcast of The War of the Worlds. Ray Bradbury imagined human conquest of the planet in The Martian Chronicles.
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