Mars has loomed large throughout human history, our imaginations filling its red vistas with fantastic detail long before our space missions returned even rudimentary photos. Back when our best observations of the Red Planet showed only a rusty disc mottled with fuzzy dark patches, people debated whether those marks were natural features, or perhaps the engineering projects of technologically advanced Martians, or maybe something wilder: In 1912, the Salt Lake Tribune ran a headline that read “Mars Peopled by One Vast Thinking Vegetable!,” accompanied by an illustration of a mossy-looking Mars, with one enormous eyeball on a stalk protruding out into deep space.

Because we have imagined Mars so long, it’s easy to forget that Mars’ history is its own. Written into the desert are bygone epochs of the Red Planet, hidden beneath plains peppered with cantankerous-looking boulders, their expanse interrupted by shining, silken dunes and towering volcanoes. Modern Mars research tells us this landscape once boasted vast stretches of water, a warmer climate, and thicker atmosphere, but all have since been lost, leaving the cold, dry surface we see today. In some places, tire tracks mark the record of human exploration—at least by our robotic avatars, the Mars rovers. While Mars is a “dead” planet in the sense of having no notable geologic activity and no known forms of life today, it still has weather (including the massive global dust storm now enfolding NASA’s long-lived Mars Opportunity rover). Unlike the moon, where the entire record of humanity’s off-Earth adventures lays written and unperturbed in the lunar dust, Mars’ winds will eventually wipe these rover tracks away.

For would-be explorers of Mars, these barren plains are a tempting destination—but why anyone wants to go to Mars depends on whom you ask. Some look at the pristine landscapes and imagine that they may answer some of our most pressing questions about the origins and evolution of life in the universe: Has life ever existed on another world? Might it still exist under the Martian surface today? If Mars has ever had life, how different (or not) is it from the life we find on Earth? And if life never got started there (or started, but failed to flourish)—why? Mars’ proximity, and the (relative) ease of translating terrestrial exploration tools to its rocky surface, makes it one of the prime places to both ask and answer these questions.

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