Planet X has a mass of M and a radius of R. Planet Y has a mass of 3M and a radius of 3R. Identical satellites orbit both planets at a distance R above their surfaces, as shown above. The planets are separated by such a large distance that the gravitational forces between them are negligible. How does the gravitational field gX at the surface of Planet X compare with the gravitational field gY at the surface of Planet Y?

gX=9gY

g sub X equals, 9 g sub Y

gX=3gY

g sub X equals, 3 g sub Y

gX=13gY

g sub X equals, one third g sub Y

gX=19gY