Saturn's Icy Moon Rhea: a Prediction for Bulk Chemical Composition and Physical Structure at the Time of the Cassini Spacecraft First Flyby

I report a model for the formation of Saturn's family of mid-sized icy moons to coincide with the first flypast of Rhea by the Cassini Orbiter spacecraft on 26 November 2005. It is proposed that these moons had condensed from a concentric family of orbiting gas rings that were cast off some 4600 Myr ago by the contracting proto-Saturnian cloud. Numerical and structural models for Rhea are constructed on the basis of a computed bulk chemical mix of hydrated rock (mass fraction 0.385), H2O ice (0.395), and NH3 ice (0.220). The large proportion of NH3 in the ice mass inhibits the formation of the dense crystalline phase II of H2O ice at the satellite's centre. This may explain the absence of compressional features on the surface. The favoured model of Rhea has a chemically uniform interior and is very cold. The satellite is nearly isodense and the predicted value of the axial moment-of-inertia factor is C/MR^2 = 0.399 +/- 0.004. NH3 is unstable at Saturn's distance from the Sun, except near the polar regions of the satellite. Perhaps the Cassini Orbiter will discover indirect evidence for NH3 through the sublimative escape of this ice from the outer layers, especially near the equatorial zones. Wasting of NH3 would weaken the residual soil, so making the edges of craters soft and prone to landslides. It will be exciting to learn what Cassini discovers.Comment: This paper was submitted to the Publications of the Astronomical Society of Australia (PASA) on 30 November 200

Nystrom Methods in the RKQ Algorithm for Initial-value Problems

We incorporate explicit Nystrom methods into the RKQ algorithm for stepwise global error control in numerical solutions of initial-value problems. The initial-value problem is transformed into an explicitly second-order problem, so as to be suitable for Nystrom integration. The Nystrom methods used are fourth-order, fifth-order and 10th-order. Two examples demonstrate the effectiveness of the algorithm.Comment: This is an extension of ideas published in J. Math. Res. (open access); see refs [1] and [2

Saturn: Origin and composition of its inner moons and rings

The contraction of the primitive protosaturnian cloud, using ideas of supersonic turbulent convection was modeled. The model suggested that each of Saturn's inner moons, excepting Rhea, condensed above the ice-point of water and consists primarily of hydrous magnesium silicates. The satellite mean densities steadily increase towards the planet and the rocky moons are irregular in shape

Voyager and the origin of the solar system

A unified model for the formation of regular satellite systems and the planetary system is outlined. The basis for this modern Laplacian theory is that there existed a large supersonic turbulent stress arising from overshooting convective motions within the three primitive gaseous clouds which formed Jupiter, Saturn, and the Sun. Calculations show that if each cloud possessed the same fraction of supersonic turbulent energy, equal to about 5% of the cloud's gravitational potential energy, then the broad mass distribution and chemistry of all regular satellite and planetary systems can be simultaneously accounted for. Titan is probably a captured moon of Saturn. Several predictions about observations made by Voyager 2 at Saturn are presented

Neptune's Triton: A moon rich in dry ice and carbon

The encounter of the spacecraft Voyager 2 with Neptune and its large satellite Triton in August 1989 will provide a crucial test of ideas regarding the origin and chemical composition of the outer solar system. In this pre-encounter publication, the possibility is quantified that Titron is a captured moon which, like Pluto and Charon, originally condensed as a major planetesimal within the gas ring that was shed by the contracting protosolar cloud at Neptune's orbit. Ideas of supersonic convective turbulence are used to compute the gas pressure, temperature and rat of catalytic synthesis of CH4, CO2, and C(s) within the protosolar cloud, assuming that all C is initially present as CO. The calculations lead to a unique composition for Triton, Pluto, Charon: each body consists of, by mass, 18 1/2 percent solid CO2 ice, 4 percent graphite, 1/2 percent CH4 ice, 29 percent methanated water ice and 48 percent of anhydrous rock. This mix has a density consistent with that of the Pluto-Charon system and yields a predicted mean density for Triton of 2.20 + or - 0.5 g/cu cm, for satellite radius equal to 1,750 km