def radius_sonic_point(planet_mass, sound_speed_0):
    """
    Radius of the sonic point, i.e., where the wind speed matches the speed of
    sound.

    Parameters
    ----------
    planet_mass (``float``):
        Planetary mass in unit of Jupiter mass.

    sound_speed (``float``):
        Constant speed of sound in unit of km / s.

    Returns
    -------
    radius_sonic_point (``float``):
        Radius of the sonic point in unit of Jupiter radius.
    """
    grav = 1772.0378503888546  # Gravitational constant in unit of
    # jupiterRad * km ** 2 / s ** 2 / jupiterMass
    return grav * planet_mass / 2 / sound_speed_0 ** 2