Question: Helmer Julius Hanssen, was a Norwegian sailor, pilot and polar explorer, he participated in three of the polar expeditions led by Roald Engelbregt Gravning Amundsen, was a Norwegian explorer of polar regions, he was the leader of the Antarctic expedition of 1910–12, which was the first to reach the South Pole, on which date?

full_context: Document 1: Olav Bjaaland: Olav Bjaaland (5 March 1873 – 8 June 1961) was a Norwegian ski champion and polar explorers. In 1911, he was one of the first five men to reach the South Pole as part of Amundsen's South Pole expedition.
Document 2: Amundsen Coast: Amundsen Coast is that portion of the coast to the south of the Ross Ice Shelf lying between Morris Peak, on the east side of Liv Glacier, and the west side of the Scott Glacier. Named by New Zealand Antarctic Place-Names Committee in 1961 for Captain Roald Amundsen, the Norwegian explorer who led his own expedition in 1910–12 to the Antarctic. Setting up a base at Framheim at the edge of the Ross Ice Shelf, he sledged southward across the shelf and discovered a route up the Axel Heiberg Glacier along this coast to reach the polar plateau. He was the first to reach the South Pole, December 14, 1911.
Document 3: Mount Amundsen: Mount Amundsen is a nunatak lying east of Denman Glacier, about 11 nautical miles (20 km) northeast of Mount Sandow. It was discovered by the Western Base Party of the Australasian Antarctic Expedition (1911–14) under Mawson, and named by Mawson for Roald Amundsen, the Norwegian polar explorer, who was the first to attain the South Pole.
Document 4: Roald Amundsen's South Pole Journey: Roald Amundsen's South Pole Journey (Norwegian: "Roald Amundsens sydpolsferd" ) is a Norwegian documentary film that features Roald Amundsen's original footage from his South Pole expedition from 1910 to 1912. The film was seen for the first time in 1912 and it was used by Amundsen for his traveling lectures.
Document 5: Roald Amundsen: Roald Engelbregt Gravning Amundsen (] ; 16 July 1872 – c. 18 June 1928) was a Norwegian explorer of polar regions. As the leader of the Antarctic expedition of 1910–12, which was the first to reach the South Pole, on 14 December 1911, he was a key expedition leader during the Heroic Age of Antarctic Exploration. In 1926, he was the first expedition leader for the air expedition to the North Pole, making him the first person, without dispute, to reach both poles. He is also known as having the first expedition to traverse the Northwest Passage (1903–06) in the Arctic.
Document 6: Comparison of the Amundsen and Scott Expeditions: Between December 1911 and January 1912, both Roald Amundsen (leading his South Pole expedition) and Robert Falcon Scott (leading the Terra Nova expedition) reached the South Pole within a month of each other. But while Scott and his four companions died on the return journey, Amundsen's party managed to reach the pole first and subsequently return to their base camp at Framheim without loss of life, suggesting that they were better prepared for the expedition. The contrasting fates of the two teams seeking the same prize at the same time invites comparison.
Document 7: Amundsen Bay: Amundsen Bay, also known as Ice Bay, is a long embayment 24 mi wide, close west of the Tula Mountains in Enderby Land, Antarctica. The bay was seen as a large pack-filled recession in the coastline by Sir Douglas Mawson on January 14, 1930. Seen by Captain Hjalmar Riiser-Larsen in charge of a Norwegian expedition during an airplane flight on January 15 and subsequently mapped nearer its true position by the Norwegians. The bay was mapped in detail by an Australian National Antarctic Research Expeditions party landed by aircraft in 1956 and another landed by launch from "Thala Dan" in February 1958. It was named by Mawson after Roald Amundsen, the Norwegian explorer who was first to reach the South Pole.
Document 8: Amundsen's South Pole expedition: The first expedition to reach the geographic South Pole was led by the Norwegian explorer Roald Amundsen. He and four others arrived at the pole on 14 December 1911, five weeks ahead of a British party led by Robert Falcon Scott as part of the Terra Nova Expedition. Amundsen and his team returned safely to their base, and later learned that Scott and his four companions had died on their return journey.
Document 9: Norge (airship): The Norge was a semi-rigid Italian-built airship that carried out the first verified trip of any kind to the North Pole and likely the first verified overflight on 12 May 1926. It was also the first aircraft to fly over the polar ice cap between Europe and America. The expedition was the brainchild of polar explorer and expedition leader Roald Amundsen, the airship's designer and pilot Umberto Nobile and American explorer Lincoln Ellsworth, who along with the Aero Club of Norway, financed the trip which was known as the Amundsen-Ellsworth 1926 Transpolar Flight.
Document 10: Fridtjof Nansen: Fridtjof Nansen ( ; 10 October 1861 – 13 May 1930) was a Norwegian explorer, scientist, diplomat, humanitarian and Nobel Peace Prize laureate. In his youth he was a champion skier and ice skater. He led the team that made the first crossing of the Greenland interior in 1888, traversing the island on cross-country skis. He won international fame after reaching a record northern latitude of 86°14′ during his North Pole expedition of 1893–96. Although he retired from exploration after his return to Norway, his techniques of polar travel and his innovations in equipment and clothing influenced a generation of subsequent Arctic and Antarctic expeditions.
Document 11: Robert Falcon Scott: Captain Robert Falcon Scott, (6 June 1868 – 29 March 1912) was a British Royal Navy officer and explorer who led two expeditions to the Antarctic regions: the Discovery Expedition (1901–1904) and the ill-fated Terra Nova Expedition (1910–1913). On the first expedition, he set a new southern record by marching to latitude 82°S and discovered the Polar (Antarctic) Plateau, on which the South Pole is located. On the second venture, Scott led a party of five which reached the South Pole on 17 January 1912, four weeks after Roald Amundsen's Norwegian expedition. On their return journey, Scott's party discovered plant fossils, proving Antarctica was once forested and joined to other continents. A planned meeting with supporting dog teams from the base camp failed, despite Scott's written instructions, and at a distance of 150 miles from their base camp and 11 miles from the next depot, Scott and his companions perished.
Document 12: Robert Peary: Rear Admiral Robert Edwin Peary Sr. (May 6, 1856 – February 20, 1920) was an American explorer and United States Navy officer who made several expeditions to the Arctic in the late 19th and early 20th centuries. He is best known for claiming to have reached the geographic North Pole with his expedition on April 6, 1909.
Document 13: Polheim: Polheim ("Home at the Pole") was Roald Amundsen's name for his camp (the first ever) at the South Pole. He arrived there on December 14, 1911, along with four other members of his expedition: Helmer Hanssen, Olav Bjaaland, Oscar Wisting, and Sverre Hassel.
Document 14: Helmer Hanssen: Helmer Julius Hanssen (24 September 1870 – 2 August 1956) was a Norwegian sailor, pilot and polar explorer. He participated in three of the polar expeditions led by Roald Amundsen and was one of the first five explorers to reach the South Pole.
Document 15: Matthew Henson Residence: The Matthew Henson Residence is where Matthew Henson, the African American polar explorer, lived from 1929 until his death in 1955. Largely forgotten, he was arguably the first man to reach the North Pole in 1909, as he was assigned the task of breaking trail in explorer Robert Peary's expedition. That argument is somewhat tenuous, in part because the expedition did not have the means to exactly determine the location of the North Pole and its having reached the North Pole was a matter of declaration.
ground_truth: 14 December 1911