<P> In 2011, it was announced at the American Geophysical Union Fall Meeting that a US Navy hydrographic ship equipped with a multibeam echosounder conducted a survey which mapped the entire trench to 100 metres (330 ft) resolution . The mapping revealed the existence of four rocky outcrops thought to be former seamounts . </P> <P> The Mariana Trench is a site chosen by researchers at Washington University and the Woods Hole Oceanographic Institution in 2012 for a seismic survey to investigate the subsurface water cycle . Using both ocean - bottom seismometers and hydrophones the scientists are able to map structures as deep as 97 kilometres (60 mi) beneath the surface . </P> <P> Four descents have been achieved . The first was the manned descent by Swiss - designed, Italian - built, United States Navy - owned bathyscaphe Trieste which reached the bottom at 1: 06 pm on 23 January 1960, with Don Walsh and Jacques Piccard on board . Iron shot was used for ballast, with gasoline for buoyancy . The onboard systems indicated a depth of 11,521 m (37,799 ft), but this was later revised to 10,916 m (35,814 ft). The depth was estimated from a conversion of pressure measured and calculations based on the water density from sea surface to seabed . </P> <P> This was followed by the unmanned ROVs Kaikō in 1996 and Nereus in 2009 . The first three expeditions directly measured very similar depths of 10,902 to 10,916 m (35,768 to 35,814 ft). The fourth was made by Canadian film director James Cameron in 2012 . On 26 March, he reached the bottom of the Mariana Trench in the submersible vessel Deepsea Challenger . </P>

How many times have we been to the bottom of the mariana trench