Question: has anyone reached the bottom of challenger deep

Answer: Yes, The 2009 and 2010 maximal depths were not confirmed by the series of dives Nereus made to the bottom during an expedition in May--June 2009. The direct descent measurements by the four expeditions which have reported from the bottom, have fixed depths in a narrow range from 10,916 m (Trieste) to 10,911 m (Kaikō), to 10,902 m (Nereus) to 10,898 m (Deepsea Challenger) Although an attempt was made to correlate locations, it could not be absolutely certain that Nereus (or the other descents) reached exactly the same points found to be maximally deep by the sonar/echo sounders of previous mapping expeditions, even though one of these echo soundings was made by Nereus' mothership.