 Why couldn't Dr. Mansard and his wife leave Jupiter?
Perhaps she could call one of Motwick's friends; she had no one on Ganymede she could call a real friend herself. “No one has ever landed on Jupiter. But his ship was drawn into Jupiter and lost.” “He and my mother lived on Jupiter until the oxygen equipment wore out at last. I was born and brought up there, and I was finally able to build a small rocket with a powerful enough drive to clear the planet.” “If Dr. Mansard succeeded in landing on Jupiter, why didn't anyone ever hear from him again?” she demanded.
 A human would not survive the force of acceleration that would be needed to break free of Jupiter's gravity.
 A human would not survive the force of acceleration that would be needed to break free of Jupiter's gravity.  Dr. Mansard and his wife ran out of oxygen before they could complete the repairs to their ship.  Dr. Mansard and his wife were torn apart by gravitational forces when they tried to leave Jupiter.  Dr. Mansard and his wife were unable to repair their ship after crash landing on Jupiter.