 Particular targets are Europa , due to its potential for life , and Callisto , due to its relatively low radiation dose . In 2003 , NASA proposed a program called Human Outer Planets Exploration ( HOPE ) that involved sending astronauts to explore the Galilean moons . NASA has projected a possible attempt some time in the 2040s . In the Vision for Space Exploration policy announced in January 2004 , NASA discussed missions beyond Mars , mentioning that a " human research presence " may be desirable on Jupiter 's moons . Before the JIMO mission was cancelled , NASA administrator Sean O 'Keefe stated that " human explorers will follow . " 
 Particular targets <a href='drop_aux' title='1'><mark>are</mark></a>Europa , due to its potential for life , and Callisto , due to its relatively low radiation dose . In 2003 , NASA proposed a program called Human Outer Planets Exploration ( HOPE ) <a href='null_relcl' title='2'><mark>that</mark></a>involved sending astronauts to explore the Galilean moons . NASA <a href='been_done' title='3'><mark>has</mark></a> projected a possible attempt some time in the 2040s . In the Vision for Space Exploration policy announced in January 2004 , NASA discussed missions beyond Mars , mentioning that a " human research presence " may be desirable on Jupiter <a href='null_genetive' title='4'><mark>'s</mark></a>moons . Before the JIMO mission was cancelled , NASA administrator Sean O 'Keefe stated that " human explorers will follow . " 
Particular targets Europa , due to its potential fa life , and Callisto , due to its relatively low radiation dose . In 2003 , NASA proposed a program called Human Outer Planets Exploration ( HOPE ) involved sendin astronauts to explore da Galilean moons . NASA done projected a possible attempt sum time in tda2040s . In the Vision for Space Exploration policy announced in January 2004 , NASA discussed missions beyond Mars , mentioning that a " human research presence " may b desirable on Jupiter  moons . Before the JIMO mission was cancelled , NASA administrator Sean O 'Keefe stated that " human explorers gon follow . "