When Ferdinand Magellan made the first voyage around the world, he may have been helped by the Pacific phenomenon of El Niño.

Magellan set sail from Spain in 1519 hoping to take the Spice Islands, on the equator near New Guinea. But he overshot his destination and landed on Guam, 1,500 miles away, for reasons no one has quite understood. But a new study in the journal Science points to sea conditions that smoothed Magellan’s voyage.

The seas were strangely calm when Magellan rounded the notorious Cape Horn. He sailed up the coast of Chile, making such good speed that the crew, many of whom were suffering from scurvy, could be rested.

The exceptional conditions were probably thanks to the tail end of an El Niño. The tropical seas of the Pacific grow unusually warm during El Niños, creating rising air that changes wind and weather patterns.

These allowed Magellan to turn northwest, cross the equator and sail north to Guam, avoiding the Spice Islands after he received reports of a famine there.

Eventually, Magellan arrived at the Philippines, but he was killed in a battle with natives. The ship arrived back in Spain in 1522, but with only 18 crew members surviving.