A research probe of mass \(m\) is launched vertically upward from the surface of a planet. The magnitude of the gravitational acceleration experienced by the probe varies with altitude \(z\) according to \(g(z) = \dfrac{g_0}{\left(1 + \dfrac{z}{R}\right)^2}\), where \(g_0\) is the surface gravitational acceleration at \(z = 0\) and \(R\) is a constant. Assuming atmospheric drag is negligible, what is the work done by the upward external force required to lift the probe at constant speed from \(z = 0\) to an altitude \(z = H\)?