Ah hah ! Very nice problem.
-- Since the mass is 1/2 of the Earth's mass, the gravitational forces between him
and the new planet would be 1/2 of what they are on Earth.
-- Since the distance between him and the center of the new planet is 1/2 of the
distance between him and the Earth's center, the gravitational forces between him
and the new planet would be (2)² = 4 times what they are on Earth.
-- These conditions combine to make his weight (1/2) x (4) = 2 times his earth weight.
-- He weighs 1,000 N (about 224.8 pounds) on the new planet.
(Maybe that's why they selected an astronaut for this mission who only weighs
about 112.5 pounds on Earth.)
