 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. The gravity of Ganymede was hardly more than that of Earth's moon, but the way the man picked up the limp Motwick with one hand and tossed him over a shoulder was startling: as though he lifted a feather pillow. The transparent dome of Jupiter's View was faintly visible in the reflected night lights of the colonial city, but the lights were overwhelmed by the giant, vari-colored disc of Jupiter itself, riding high in the sky. “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. Trella had the desk clerk call a cab to deliver the unconscious Motwick to his home. For some reason she decided against telling him that the assignment on which she had come to the Jupiter system was to gather his own father's notebooks and take them back to Earth. Motwick was an irresponsible playboy whom Trella had known briefly on Earth, and Trella was glad to dispense with his company for the remaining three weeks before the spaceship blasted off.
 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.