expansion into the Pacific was eastward, against steady trade winds. Sailing against the wind he argues, may have been the key to their success. "They could sail out for days into the secure in the knowledge that unknown if they didn't find anything, they could turn about and catch a swift ride home on the trade winds." For returning explorers, successful or not, the geography of their own archipelagoes provided a safety net, ensuring that sailors wouldn't sail past and be lost again in the open ocean. Vanuatu, for example, is a chain of islands 800 kilometers (500 miles) long with many islands within sight of each other. Once sailors hit that string of islands, they could find their way home.