# Gravity wells
#
# https://xkcd.com/681/

fn depth(mass: Mass, radius: Length) -> Length =
    G × mass / (g0 × radius) -> km

let earth_mass = 5.972e24 kg
let earth_radius = 6371 km

let moon_mass = 7.342e22 kg
let moon_radius = 1737 km

assert_eq(depth(earth_mass, earth_radius), 6379 km, 1 km)
assert_eq(depth(moon_mass, moon_radius), 288 km, 1 km)