THE SIDEREAL ROTATION PERIOD OF NEPTUNE

The two main, low frequency radio components discovered at Neptune by the Planetary Radio Astronomy experiment carried aboard Voyager 2 have a well defined periodicity at about 16.1 hour. By analyzing all the a vailable data, i.e. about 60 days around the closest approach for the ''Burst'' component and 15 days for the ''Smooth'' component, we deter mine, for each component, die best estimate of the radio period. We co nclude that the two estimates are not statistically different. While t he two kinds of radio emissions have very different characteristics (i n particular their frequency ranges and beaming properties), and proba bly correspond to different emission processes, their modulation is ve ry likely due to the rotation of the planetary magnetic field tied to the core of the planet, as it has already been assumed for the other g iant planets. The deduced estimate of the sidereal rotation period of Neptune is 16.108 +/- 0.006 (or 16h06.5m +/- 00.4m).