Pluto’s Moons and the Birth of the Solar System

A new theory for how our Solar system was formed – based on the physical concept of supersonic convective turbulence, computational modelling and four decades of observational data from NASA’s fleet of interplanetary space probes

Dr Andrew J. R. Prentice

School of Mathematical Sciences, Monash University & Computational Engineering and Science Research Centre, University of Southern Queensland

In February 2015, the Dawn spacecraft will reach the largest asteroid Ceres and, a few months later, the NASA New Horizons spacecraft will fly past Pluto and its family of icy moons. These impending events have stirred fresh interest in the ‘dwarf’ planets of our Solar system.

Information about Mercury and Titan gathered from the NASA Messenger and Cassini-Huygens spacecraft coupled with data from the Galileo project about Jupiter’s largest moon, Ganymede, has highlighted a remarkable diversity in the physical and chemical makeup of all of the solid planet-sized worlds in the Sun’s realm and led us to a new theory for the birth of the solar system.

Closest planet to the Sun, Mercury is remarkable because more than 70% of its mass is iron and nickel. Even more remarkably, it has a dynamo-driven magnetic field suggesting that much of the inner metal core is still molten. This is a surprise because existing theories for its thermal evolution presume that the iron should have long since solidified.

Ganymede is a chemically differentiated body, consisting of roughly equal proportions of rock and water ice. Like Mercury, it has a large native magnetic field but this is most likely a frozen-in ‘lodestone’ field created in the moon’s youth, when its rock core was much hotter and Jupiter was much more magnetically-active than it is today.

Saturn’s largest moon, Titan is distinctive for the massive atmosphere of nitrogen and methane which shrouds its surface. As methane is easily destroyed by solar radiation, some geophysical mechanism must exist which brings fresh methane from the satellite’s interior. Titan also has no magnetic field and its shape is slightly oblate – its polar regions are flatter and the equator much rounder than those expected of a naturally formed satellite.  Titan’s observed shape suggests that it condensed in a solar obit and was later captured by Saturn – an event which I first predicted in 1980 (NASA Jet Propulsion Laboratory Publication 80-80).

In this lecture, I will discuss how the physical and chemical differences between Mercury, Titan and Ganymede can be explained within the context of a modern Laplacian theory of solar system formation. The basic premise of this theory is that, about 4.5 billion years ago, both the planetary system and regular satellite systems of the gas giant planets, Jupiter and Saturn, condensed from concentric families of orbiting gas rings. These rings were cast off by the primitive solar cloud and the proto-planetary clouds which formed Jupiter and Saturn. The physical mechanism for shedding isolated gas rings is very strong turbulent stress created by supersonic convective currents within each of the gravitationally contracting clouds.

I will apply this theory to explain how Pluto and its largest moon Charon were formed and suggest the origin of the recently-discovered smaller moons of Pluto orbiting beyond Charon, whose existence I predicted over 20 years ago (Prentice 1993, Aust. J. Astron. Vol.5, p.111-119). In conclusion, I will make several new predictions for the internal make up of Pluto, Charon and Ceres. These predictions will have to wait to be tested when New Horizons passes by in 2015.

The lecture is to be illustrated with many colourful images from space and is pitched to suit a general audience with a thirst for knowledge and an open mind.