Astronaut/Oceanographer Dr. Kathy Sullivan is now the only human to walk in space AND reach the Challenger Deep - the lowest known point in the ocean. . Read this the_explorers_club story at Discovery.com/universalexplorer . 📸 Enrique Alvarez . . #astronaut #VictorVescovo #challengerdeep #ocen #worldoceansweek #exploration #KathrynSullivan #MarianaTrench #ecflag