He was one of the first five people to reach the South Pole on 14 December 1911, along with Roald Amundsen, Olav Bjaaland, Oscar Wisting, and Sverre Hassel. During their stay at the South Pole, it is estimated that Hanssen passed within 200 yards (180 meters) of the mathematical South Pole point. This was during one of his ski runs which Amundsen had ordered be performed to completely encircle or "box" the pole, to ensure that there was no doubt that the expedition had attained the pole. For his participation in the expedition, he was awarded the South Pole Medal ("Sydpolsmedaljen"), the Royal Norwegian award instituted by King Haakon VII in 1912 to reward participants in Roald Amundsen's South Pole expedition.