From canals to Curiosity The search for life on Mars

Mars has long ignited our imagination. Ben Evans traces the history of our quest for life on the fourth rock from the Sun

- Ben Evans

The prospect of life on Mars - Earth's planetary next-door neighbour, an alien world that betrays tantalising hints of a watery past - has bewitched humanity for centuries. From the 'canals' seen by astronomer Percival Lowell, and HG Wells's fire-spewing tripods, to David Bowie's glam-rock croons about a girl with mousy hair, life on Mars has captured our imagination as a literal and metaphorical trope.

At first glance, the contrast between the iridescent blues, greens and tans of Earth - awash with water, teeming with life - and the barren, subfreezing, radiation-drenched Mars could hardly be more stark. Half the size of Earth and 11 per cent as massive, Mars's orbit around the Sun takes it as near to us as 56 million km (35 million miles) and as far as 400 million km (250 million miles).

Yet the pair do share similarities. Mars's 24-hour, 36-minute day mirrors our 23 hours, 56 minutes. Its axial tilt of 25.19° is close to our 23.44°, producing similar seasons. But Martian seasons last nearly twice as long, the planet's more distant orbit taking 687 days to circle the Sun compared to Earth's 365 days.

Life on Mars has long sat at the forefront of human imagination. Early ideas regarded the Red Planet as little more than a volcanic wasteland. But in the 19th century, it adopted a new persona: a utopia, with 'Martians' exhibiting character traits of decadence and enlightened intelligence. One story even imagined them aging backwards, like otherworldly Benjamin Buttons.

Canals and dead ends