Question

In order to measure the mass of an alien planet, imagine you put a spacecraft moving in a circular orbit of radius 400000 km around this planet. You happen to be located in the plane of the spacecraft's orbit. You find that the spacecraft's radio signal varies periodically in wavelength between 4.99979 mm and 5.00021 mm .

Assuming that the radio is broadcasting normally, at a constant wavelength, what is the mass of the planet?

Answer 1