Why do warm Neptunes present nonzero eccentricity?

Most Neptune-mass planets in close-in orbits (orbital periods less than a few days) present nonzero eccentricity, typically around 0.15. This is somehow unexpected, as these planets undergo strong tidal dissipation that should circularize their orbits in a timescale shorter than the age of the system. In this paper we discuss some mechanisms that can oppose to bodily tides, namely, thermal atmospheric tides, evaporation of the atmosphere, and excitation from a distant companion. In the first two cases, the eccentricity can increase consistently, while in the last one, the eccentricity can only be excited for a limited amount of time (that may nevertheless exceed the age of the system). We show the limitations of these different mechanisms and how some of them could, depending on specific properties of the observed planetary systems, account for their presently observed eccentricities.

The Determination of Love's Number K from Tidal Variations of Rotation of a Compressible Earth

Long period bodily tides (fortnightly and monthly) cause periodic changes of the Earth's moment of inertia and consequently the angular speed of its rotation.During the past few years the use of atomic clocks has made it possible to determine the amplitudes of these periodic variations of the Earth's rotation with high accuracy and has made this method very effective in determining Love's number K, which is dependent on the internal structure of the Earth (the most detailed studies were made in the U.S.S.R. – Pilnik and Gubanov).But up to now it was taken (Anderson, Woolard, Melchior, and others), that the formulae of Jeffreys and Woolard, which are used in this method, are valid only for incompressible Earth models.It is shown in this paper that the formulae are valid for the case of an actual compressible heterogeneous Earth. Thus, the method receives a real practical value. The use of lasers and radio methods in the near future will make this method even more effective.The full text of the paper will be published in the magazine Physics of the Earth in No. 3, 1972.