the mass of the iceshield / mass of the moon = 5 10^-4. But at a distance of 2000km compared to 4 10^5 km for the moon, the iceshield should have similar gravitational pull. the inverse square of 2000km / the inverse square of 4 10^5 km = 4 10^4. (4e4=(1/2000000^2)/(1/(4e8)^2))

Distance and mass seem to cancel out almost perfectly