A billion-dollar volley of space missions, due to start on Monday, may at last answer the question: does life, or the potential for it, exist on the Red Planet?
A bloodied body named after the Roman god of war; the home of "canals" spotted by astronomer Percival Lowell; of terrifying aliens in H.G. Wells' "The War of the Worlds"; or a verdant twin for Earth in Ray Bradbury's "The Martian Chronicles": Mars holds a central place in our imagination of the cosmos.
No other planet has been targeted by so many space probes, not least because Venus, Earth's closest neighbour, is an uninhabitable hellhole with an atmosphere of toxic soup.
But the mission record is littered with disasters, and those few that have succeeded only seem to have swollen the great martian mystery with each turn.
Before the probe Mariner landed in the 1960s, the public was expecting another Earth, "a green, inhabited planet full of oceans," the European Space Agency (ESA) notes.
That dream was shattered when the first fuzzy pictures revealed a dry, cold, dusty and airless world, and the barren image was confirmed by the Viking probes in the 1970s.
So it remained for the following two decades, until extraordinary photographs garnered by American orbiters showed that Mars has thin polar water ice caps.
Dry river beds and sedimentary layers of rock also show that, several billion years ago, in its infancy, the planet was awash with surface water, scientists believe.
And some of them claim Mars may still have huge quantities of the precious stuff, lying just below its surface.
The quest to answer this agonising speculation begins on Monday, when a European orbiter, Mars Express, is hoisted aloft by a Soyuz-Fregat launcher from Russia's space base in Kazakhstan.
If all goes well, the unmanned 190-million-dollar spacecraft will hurtle across 400 million kilometers (250 million miles), taking up station off Mars just before Christmas, its seven cameras, radars and spectrometers ready to scour the planet's surface from orbit.
It will then launch a miniature lab which will descend to the equatorial region of the Isidis Basin, to test the martian soil.
The 55-million-dollar stationary lander -- its round shape recalling "a tiny garden barbecue" in the words of one of its inventors -- has been dubbed Beagle-2, in honour of the sailing ship that took Charles Darwin on his epic voyage into the origins of life.
It is the first time that Western Europe has ever launched a solo exploration of another planet.
But it is also a critical test of ESA's gamble that it can successfully carry out small, quick, cheap missions. This strategy has its critics, who say it can cut too many corners in design and testing in comparison with bigger, lavishly-funded long-term projects.
The other two missions to Mars will follow in quick succession, and both are American, using wheeled roving robots that will be deployed to the surface to pick up and analyse soil samples.
The first Mars Exploration Rover is scheduled to lift off from June 8, arriving on January 4, while its twin is pencilled for launch on June 25 2004, arriving on January 25; the cost of the two missions is put at more than 800 million dollars.
One site is the Gusev Crater, a giant crater that may have contained a lake, while the other, Meridiani Planum, on other side of the planet, has deposits of an iron oxide considered a "chemical signature" of past water, says NASA.
An eternal place in the pantheon of space science is reserved for whether it is the Europeans and Americans who first confirm liquid water on Mars.
But, says Colin Pillinger, the force behind Beagle-2, "it's not a competition. We are all doing science and we will all share it. I don't believe in monopolies."
He adds: "For 5,000 years, people have been looking up in the sky and wondering what this strange red object is and wondering 'is there life out there?'
"We are the generation that now have the chance to answer it."