January 2011 General Meeting Report
Guest Speaker Dr Andrew Prentice, and his subject ‟New Insights into the Origin of our Solar System”
Andrew Prentice is an Australian mathematical genius and an accomplished astrophysicist. Establishing and using his theory of supersonic turbulence he is known for having made a range of unorthodox yet accurate predictions about the solar system by inserting supersonic turbulence into what has become the Modern Laplacian Theory. It has caused quite a stir in the traditional views of solar system formation. Renowned for his quirky style, he has motivated numerous Monash mathematics and astrophysics students with his humorous anecdotes and random utterances, many of which have become folklore amongst Monash students and staff. A collection of these ‟Prenticisms” can be found on Facebook under ‟Prentice Appreciation Society”.
Most of our readers will be familiar with Andrew’s pet subjects: Supersonic Turbulence and the Modern Laplacian Theory of the origin of our solar system(see Laplace’s Theory), from his previous talks at the ASV. As well as his ongoing struggle for recognition of his work by his astronomical peers. This presentation concentrated on new insights gleaned from the current Cassini-Huygens mission to Saturn and Titan and the Messenger mission to Mercury. Considering all the new space technology and the hundreds of exoplanets discovered it is surprising that there is not yet a clear understanding of the mechanism by which planets and planetary systems form; despite the great wealth of information about those systems that has already been gathered by interplanetary space probes and Earth-based measurements. Exactly 30 years have now elapsed since the visits of the Voyager 1 and 2 spacecraft to Saturn. Today, the Cassini-Huygens Mission to Saturn and Titan is slowly unravelling the mysteries of Saturn and its remarkable satellite system. Saturn’s largest satellite Titan is more like a planet than a moon. Its mass is nearly 60 times larger than that of the second largest moon Rhea and its physical size exceeds that of iron-rich Mercury. Titan is also unique because of its thick atmosphere which is 4 times denser than that of the Earth at its surface. A surprising feature of Titan is its slightly oblate shape, as revealed by the Cassini radar experiment. Such a shape lends support to the idea that Titan originally condensed as a secondary embryo in the gas ring that was shed by contracting protosolar cloud at Saturn’s orbital distance from the Sun. By forming in a free orbit Titan’s shape would have initially been oblate, like the asteroid Ceres. Its bulk chemical composition is predicted to be anhydrous rock (see Anomalies of Saturn Moons). It is suggested that Titan’s capture by the proto-Saturnian system was secured by collision with one or both of 2 volatile-rich native moons of Saturn that once existed at 17RSat and 24RSat, where RSat is Saturn’s equatorial radius. It is the NH3 and CH4 ices of those lost moons which are the source of Titan’s N2–CH4 atmosphere. If Titan’s outer ice mantle was still warm at the time of capture, then its shape would soon relax via tidal dissipation to that demanded by the moon’s new orbit about Saturn. The shape of the cold inner core might, however, retain its oblate shape. Titan’s shape today is thus the outcome of an amazing and complex dynamical past (see Titan Post Cassini Model).
According to Andrew’s ‘Modern Laplacian Theory’ of solar system origin model, planets condense from an orbiting family of gas rings that are shed by a gravitationally contracting proto solar cloud at the equator of the rotating cloud as a means for disposing of excess spin angular momentum (see Modern Laplacian Theory). Very strong thermal convection within the cloud provides the mechanism for the shedding of discrete gas rings, rather than a continuous nebula. The temperatures of the gas rings vary with mean orbital radius (see Gas Ring Properties). The chemical condensation sequence for the inner planets is shown here (see Chemical Condensation Sequence). Mercury consists mostly of Fe-Ni (67% by mass) and has a concentration of Thorium and Uranium that is 4.3 times the terrestrial value. This allows us to explain why the outer core of the planet is still molten: the blistering hot ceramic mantle inhibits the escape of heat from the interior. A partly molten interior has been deduced from the large librations of the Mercurian crust and the existence of the planet’s large dipole magnetic field (see Mercury Chemical Masses) .
It will be interesting to wait and see if Andrew’s predictions are once more borne out by future discoveries. The presence of water in the solar system and its origin is often the subject of much debate. Earth is sometimes depicted as the watery planet, but as a bit of trivia Andrew told us, if all the water on Earth was concentrated in one spot, shaped into a round drop, its diameter would be less than 1000km (see Water and Air in perspective).
After a lively and extensive question time the vote of thanks was given by Ross Berner, Director Cosmology Section, to general acclaim. AK