numbat/examples/xkcd_681.nbt

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

use extra::astronomy

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

print("Gravity well depths:")
print("Sun     {well_depth(solar_mass, solar_radius):8.0f}")
print("Earth   {well_depth(earth_mass, earth_radius):8.0f}")
print("Moon    {well_depth(lunar_mass, lunar_radius):8.0f}")
print("Mars    {well_depth(mars_mass,  mars_radius):8.0f}")
print("Jupiter {well_depth(jupiter_mass, jupiter_radius):8.0f}")

assert_eq(well_depth(earth_mass, earth_radius), 6379 km, 1 km)
assert_eq(well_depth(mars_mass,  mars_radius),  1286 km, 3 km)
assert_eq(well_depth(lunar_mass, lunar_radius),  288 km, 1 km)