The Open Polar Sea was a hypothesized ice-free ocean surrounding the North Pole. This unproved and eventually-disproved theory was once so widely believed that many exploring expeditions used it as justification for attempts to reach the North Pole by sea or to find a navigable sea route between Europe and the Pacific across the North Pole. History The theory that the North Pole region might be a practical sea route goes back to at least the 16th century, when it was suggested by English cartographer Robert Thorne (1492-1532). The explorers William Barents and Henry Hudson also believed in the Open Polar Sea. For a time, the theory was put aside because of the practical experience of navigators who encountered impenetrable ice as they went north. However, the idea was revived again in the mid-19th century by theoretical geographers, such as Matthew F. Maury and August Petermann. At the time, interest in polar exploration was high because of the search for John Franklin's missing expedition, and many would-be polar explorers took up the theory, including Elisha Kent Kane, Dr. Isaac Israel Hayes, and George Washington De Long. It was believed that once a ship broke through the regions of thick ice that had stopped previous explorers, a temperate sea would be found beyond it. Support Although it is now known that the North Pole was covered with thick ice for much of the period, the Open Polar Sea was a popular theory in the 16th to the 19th centuries, and many arguments were made to justify its existence: Since sea ice was erroneously believed to form only near land, if there were no land near the North Pole, there would be no ice. Since there is perpetual sun during the Arctic summer, it would melt all the ice. Russian explorers had found large polynyas (areas of open water) north of Svalbard and so there were surely other areas of open water elsewhere. Maury, Petermann, and other scientists who studied ocean currents in the 19th century hypothesized that warm northward currents such as the Gulf Stream and Kuroshio Current must rise to the surface and result in an ice-free sea near the pole. Extrapolation of temperature readings taken in subpolar regions indicated that the region of greatest cold would be at about 80°N, instead of at the North Pole. Migration patterns of certain animals seemed to suggest that the polar region was