More than 100 years ago, Italian astronomer Giovanni Schiaparelli peered through his telescope and saw channels and grooves etched across the surface of Mars. The canali, as he called them in 1877, gave rise to incredible science fiction stories about intelligent aliens having engineered the strange structures. A century later, spacecraft and astronomical probes revealed not the handiwork of Martians, but compelling evidence that vast quantities of water once washed across the surface of Earth’s planetary neighbour, carving out deep canyons, channels and coastlines. But the water had long vanished from the now dusty, rusty Martian surface. All that scientists have been able to detect are small amounts of water in the Martian ice caps and a bit wafting around the hazy, pink atmosphere. The missing water has been one of the most perplexing mysteries in planetary science: Was it blasted away by some cosmic disaster? Did it somehow leak out of the Martian atmosphere? Or did it, as scientists are reporting this week, seep underground, remaining there to this day? An international team, using NASA’s Odyssey spacecraft, say they have collected compelling evidence that a huge amount of water is locked underground in a Martian version of permafrost. Or “buried treasure,” as William Boynton, a planetary scientist at the University of Arizona, describes it.