As Europe and the United States prepare to launch missions to Mars, BBC News Online's Helen Briggs looks at our long-running fascination with the idea of Martian life.
"Ladies and gentlemen, I have a grave announcement to make," said the newscaster. "Incredible as it may seem, strange beings who landed in New Jersey tonight are the vanguard of an invading army from Mars."
So goes the broadcast that sparked panic in pre-war America. There were tales - largely misreported - of people hiding in cellars, clutching loaded guns, and thousands fleeing their homes.
The idea of colonising Mars owes much to science fiction
The performance, on the eve of Halloween in 1938, was in fact a news-style adaptation of the HG Wells novel The War Of The Worlds.
The science fiction classic tells the story of a doomed race of hi-tech Martians landing in southern England to try to take over Earth.
There were, of course, no wriggling snake-like monsters emerging from spaceships that autumn day.
But the incident seeped into a corner of the human psyche that has long been fascinated by the idea of little green men from Mars.
God of War
Charles Cockell, a Mars biologist at the British Antarctic Survey in Cambridgeshire, UK, says it dates back long before telescopes.
"The fascination has been there for centuries," he says. "Ancients saw this thing that was slightly different in the sky - it appeared to wander across the sky and had a red colour."
In Assyria, Mars was known as the "shedder of blood" while the Vikings, Greeks and Romans called it the God of War. It is easy to imagine why the planet looked to ancient civilisations like a drop of blood in the sky.
We now know that Mars is red due to oxidised iron materials - rust - in the surface rocks. And its elliptical orbit means it is only close to Earth for a couple of months in any two-year stretch before swinging away again.
The advent of telescopes brought more myths about Mars. Italian astronomer Giovanni Schiaparelli announced the discovery of "canali" (channels) on Mars in 1877.
It fuelled speculation that he had seen artificial canals built by an intelligent civilisation, inspiring a host of science fiction books.
By the early 1960s, when a robotic space craft first visited Mars, the idea of some form of extra-terrestrial life had seeped into the human consciousness.
It came as a shock when the first close-up images of the planet revealed not lush vegetation but a barren, hostile wilderness.
Since then Mars has been visited by more space craft than any other planet providing a tantalising glimpse of a world that could once have had water, oceans and life.
However, the chances are that if there ever was primitive life on Mars, there will only be fossils left for space probes and future astronauts to discover.
Could these gullies have been carved by running water?
But, as Bo Maxwell, of the UK branch of the Mars Society, puts it, the thought doesn't quell the human urge to explore.
"It's the very essence of mankind," he says. "Are we alone - is this all that we are?"
Many writers have dreamed of a day when Mars becomes our future - a place with water and sunlight where we can leave the Earth behind.
But there is another possibility, says Mark Adler of the US space agency (Nasa).
"Earth and Mars exchanged material in the early days when life was forming on Earth," says the deputy mission manager for the Mars Exploration rovers.
"Was Mars part of our past? Maybe we are the Martians."