The dynamical history of the evaporating or disrupted ice giant planet around white dwarf WD J0914+1914

ABSTRACT Robust evidence of an ice giant planet shedding its atmosphere around the white dwarf WD J0914+1914 represents a milestone in exoplanetary science, allowing us to finally supplement our knowledge of white dwarf metal pollution, debris discs, and minor planets with the presence of a major planet. Here, we discuss the possible dynamical origins of this planet, WD J0914+1914 b. The very young cooling age of the host white dwarf (13 Myr) combined with the currently estimated planet–star separation of about 0.07 au imposes particularly intriguing and restrictive coupled constraints on its current orbit and its tidal dissipation characteristics. The planet must have been scattered from a distance of at least a few au to its current location, requiring the current or former presence of at least one more major planet in the system in the absence of a hidden binary companion. We show that WD J0914+1914 b could not have subsequently shrunk its orbit through chaotic f-mode tidal excitation (characteristic of such highly eccentric orbits) unless the planet was or is highly inflated and possibly had partially thermally self-disrupted from mode-based energy release. We also demonstrate that if the planet is currently assumed to reside on a near-circular orbit at 0.07 au, then non-chaotic equilibrium tides impose unrealistic values for the planet’s tidal quality factor. We conclude that WD J0914+1914 b either (i) actually resides interior to 0.07 au, (ii) resembles a disrupted ‘Super-Puff’ whose remains reside on a circular orbit, or (iii) resembles a larger or denser ice giant on a currently eccentric orbit. Distinguishing these three possibilities strongly motivates follow-up observations.

Averaging of Earth-Crossing Orbits

The orbits of planet-crossing asteroids (and comets) can undergo close approaches and collisions with some major planet. This introduces a singularity in the N-body Hamiltonian, and the averaging of the equations of motion, traditionally used to compute secular perturbations, is undefined. We have shown (Gronchi and Milani, 1998) that it is possible to define in a rigorous way some generalised averaged equations of motion, in such a way that the generalised solutions are unique and piecewise smooth, with corners on the node crossing lines.The model is the averaged equations of motion first introduced by Kozai (1962): the perturbing planets are assumed to move in circular, coplanar orbits, and the equations of motion are averaged over the anomalies of the asteroid and of the planets. In the non-crossing case the averaging is integrable; in the planet-crossing case there is a polar singularity of order two in the equations of motion, and averaging is not possible. To define a generalized solution, we decrease the order of the polar singularity by the method of extraction of the singularities by Kantorovich. The singularity of the perturbing function is approximated by a modified inverse distance, the one between the straight lines tangent to the two orbits at the nodal points. In this approximation the averaged perturbing function has an analytical expression, allowing explicit computation with elliptic integrals and elementary functions.

The eccentric ringlet at 1.29 RS

We present preliminary results of an examination of the eccentric ringlet near 1.29 R, in Saturn's inner C ring. Situated near the Titan 1:0 apsidal resonance, this feature provides an opportunity to study the behavior of a ring under the influence of both the gravity field of a major planet and the potential of an external satellite.The data sets used for this analysis consisted of seven Voyager images of this ringlet, ranging in resolution from 60 to 5 km/pixel, plus data obtained from three UVS stellar occultations and one Radio Science occultation. Three observations occurred within a day of Voyager 1 closest approach and seven within 5 days of Voyager 3 closest approach. The Voyager encounters were separated by 286 days. Of the seven Voyager images used, only the three highest resolution frames were corrected for geometric distortion. Therefore, the results presented here must be considered preliminary.

A Review of Dynamical Evidence Concerning a Former Asteroidal Planet

This paper is a brief review of results presented elsewhere (Van Flandern 1977, 1978). The conclusion of these results is that at least the comets, and probably also the asteroids and meteorites, originated in the breakup of a major planet in the present location of the asteroid belt, at an epoch of just 5×106 years ago. Although there are many “well-known facts” about the solar system which seem to contradict this conclusion, these contradictory “facts”, upon closer examination, are often not so convincing as we have been inclined to assume; in each instance so far suggested there is a plausible alternative interpretation of the data which is supportive of the breakup hypothesis. A compelling contradictory argument has not yet surfaced. In view of this, and in consideration of the strength of the arguments favoring the hypothesis, it will be necessary to judge the conclusion on the merits of the case, without the intervention of the apriori decision that it cannot be true.

3. A Former Major Planet of the Solar System

Dynamical calculations by Ovenden, indicating the former existence of a 90-Earth-mass planet in the asteroid belt, have now been supported by a study of orbital element distributions of very-long-period comets. The indicated epoch for disintegration of the planet is just 5 x 106 years ago.