General Meeting Report March.
DR Andrew Prentice, School of Mathematical Sciences Monash University,
speaks on the Cassini-Huygens Mission, what have we learned so far?
Situated between the Melbourne Botanical Gardens and the Shrine of Remembrance Park the National Herbarium (current home to the Astronomical Society of Victoria) normally has the secluded atmosphere of a quiet Suburban environment. Parking poses no problems as there is little traffic using Birdwood Avenue in the evenings; except of course the perennial joggers pounding the paths around the Gardens. Ever-so-often though, this idyllic situation is harshly broken when promoters entice half of Melbourne’s population to attend either a major Myer Music Bowl event, or when the Shakespearian Players perform their Midsummer Nights Dreams. But an event even bigger than any of the above, the Commonwealth Games / Grand Prix, did force us to an alternate site for the March meeting, and Andrew Prentice was able to give his scheduled talk to the ASV on his home turf in Monash.
Collaborating with his ASV namesake at the controls of the projector, Andrew lead us through the latest information on the Cassini mission to the planet Saturn. Cassini-Huygens is a joint NASA/ESA/ASI space mission to study Saturn and its moons. It was launched on October 15, 1997 and entered into orbit around Saturn on July 1, 2004. The Huygens sensing probe descended to the surface of the moon Titan on January 15, 2005. Cassini, named after the French-Italian astronomer who discovered the division in Saturn’s rings, Giovanni Domenico Cassini, is the fourth spacecraft to visit Saturn, but the first to go into orbit around the planet. Too far from the Sun for solar panels it gets its power from three radioisotope thermoelectric generators, which use heat from the natural decay of plutonium to generate direct current electricity. Designed for a long operational lifetime the system will, at the end of the 11-year Cassini mission, still be capable of producing some 628 watts of power.
Prentice, with his Super-sonic Turbulence Theory on planetary formation has again made some startling prediction on composition and density of the moons of Saturn. It’s been nearly two years since NASA’s Cassini spacecraft slipped into the Saturnian system. In that time astronomers have learned much about Saturn, its rings and its moons from it. And, not surprisingly for us, a lot of the information collected tallies with the predictions made by Dr Andrew Prentice.
Giving us a quick refresher course on Laplace’s nebula hypothesis, Andrew led into the significance of his Supersonic Turbulence theory in planetary system and moon formation. Presented as the Modern Laplacian Theory it explains much of the process of gravitational settling of the condensate grains onto the mean orbit of the system’s gaseous rings, while separating the fast and slow gases in layers from the rocky ice stream. Despite the many confirmed predictions Prentice has made on planetary formation and composition using this approach, the struggle for recognition by the official establishment seems to continue unabated. He takes it all in his stride, though; if anything he uses it to his advantage as an identifying trade mark of his work. His energetic enthusiasm and persistent determination over the years are an inspiration to any would-be astrophysicist, and his visionary insight into planetary system formation seems to be without limit. He sees Titan as a captured solar planet that collided with another Rhea sized moon of Saturn; the left-over remnant being the odd-shaped moonlet Hyperion. Cassini should, Prentice says, in time discover mass anomalies in the upper mantle of Titan that correspond with burial sites of at least one former native moon of Saturn. Predictions for the icy moon Rhea are: a very cold, chemically uniform interior that is isodense and has an axial moment-of-inertia factor of C/MRA2 = 0.399 +/- 0.004. ‟Remember that equation” Prentice reiterates in his inimitable style as he circles it on the screen with a red laser pointer, ‟when it is confirmed, remember I predicted it”.
The current model for the formation of Saturn’s family of icy moons proposes that the mid-sized moons condensed from water and rock in the concentric gas rings that were shed by the contracting proto Saturnian cloud. The thermal evolution curve predicts that Enceladus (with 99% reflectivity it has the highest known albedo of any body in the solar system) has a rock fraction of 0.574. He leaves us musing whether the old slide projectors gave a more natural picture than the newfangled liquid crystals. “I think the colours were softer, don’t you think?”
The vote of thanks was given by Barry Adcock with the customary, gold-wrapped ASV port, and an invitation to tell us more about it in a future visit.