Andrew Prentice makes daring prediction for Saturn's tiny moon Enceladus

The Cassini Spacecraft is about to throw another challenge at the Modern Laplacian theory of solar system formation.

This Thursday 17th February, at 0330 hours UTC (Melbourne time: 1330 hours), the Cassini Orbiter will make its first close flypast of Saturn's small moon Enceladus. Enceladus is a mysterious moon since its weight is not known. The current best estimate of the mean density is 1.8 +/- 0.2 gram per cubic centimetre. That is, its density should lie between 1.6 and 2.0 times that of pure liquid water. This has a density of 1.0 gram per cubic centimetre (gm/cc). The conclusion that Enceladus may turn out to be some 80% heavier than water has been reached by the NASA Jet Propulsion Laboratory orbital ephemeris group. This group is responsible for keeping track of the Cassini spacecraft and the orbital positions of all of the moons of Saturn.

This is where the challenge lies for the Modern Laplacian theory (MLT). Enceladus orbits Saturn between Mimas and Tethys. As such its mean density should also lie between those of these two neighbours. Tethys has a mean density of 1.0 gm/cc and Mimas a density of 1.16 gm/cc.

In a paper that went online on February 4, 2005, and which has been accepted for presentation to the 36th Annual Meeting Lunar and Planetary Society, to be held in Houston, USA from March 14-18, Dr Prentice has predicted that Enceladus and Tethys are near twins as far as their bulk chemical composition is concerned. Each body should contain about 10% by weight of rock and 90% of frozen water ice. This yields a mean density of 1.0 gm/cc for both bodies.

So the value which the MLT predicts for the Enceladus mean density is signicantly less than the JPL orbital ephemeris value. Bob Jacobson [JPL] has advised me not to lose heart since Enceladus is still up for grabs, even although there is less than a 1 in 30,000 chance that its density will prove to be as a low as 1.0 gm/cc. This is because the Saturn system is an extremely complex one to model even with the very best of information and computers. And when the Voyager spacecrafts took distant photographs of Enceladus, nearly 25 years ago, some scientists later noticed that the shape of Enceladus was consistent with it having a density of only 1.0 gm/cc. The nice thing about the MLT is that this value (as well as the actual chemical composition of Enceladus) pops naturally out of the theory.

Full text of Dr Prentice's prediction (pdf)

WHAT HAPPENED WITH DR PRENTICE AND TITAN?

Dr Prentice's prediction that Titan should prove to be a 'vast barren landscape of smooth ice with very few craters', which appeared in the Sydney Morning Herald on Tuesday October 26, one full day before the the first close flyby of the Cassini spacecraft, seems to be holding. So far not a single crater has been found either by Cassini or the Huygens Probe. The Cassini Radar altimeter experiment also reported on October 28, 2004, that 'Titan is remarkably flat'.

See http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=1172 for further details.

For further information contact Dr. Prentice at:
Phone: +61 3 9905 4499
Email: andrew.prentice [at] sci.monash.edu.au
Bulletin prepared 15 February, 2005

CSPA Scientist Andrew Prentice predicts Phoebe composition

ANDREW PRENTICE SURVIVES ENCOUNTER WITH PHOEBE

Today, June 23 2004, the Cassini Project announced the discovery of large-scale deposits of carbon dioxide on the surface of Saturn's outermost orbiting satellite Phoebe and a mean density for this ancient, battered moon of 1.6 grams per cubic centimetre. Prior to these discoveries, Monash University scientist Andrew Prentice had predicted three different possible bulk chemical compositions and mean densities for Phoebe based on his controversial theory of Solar system origin (see below).

Three possible compositional models (options) for Phoebe needed to be considered as no one knew exactly from where this moon had originated. Unlike Saturn's other main satellites, which all revolve on circular orbits close to the planet and in the same common direction as defined by the planet's own spin, Phoebe's orbit is highly eccentric and the moon also goes around the planet in the opposite direction. This suggests that Phoebe is a captured, rather than being a native, moon of Saturn.

Prentice's option 1 model assumed that Phoebe condensed at Saturn's distance from the sun from a gas ring that was shed some 4 billion years ago by the primitive cloud of gas that went on to form the Sun itself. The condensate from this model consists of rock, water ice and graphite and has a mean density of 1.33 grams per cubic centimetre (g/cc). This model is clearly ruled out by the Cassini data, not only since the density is too low but mostly because it is unable to explain the ubiquitous presence of carbon dioxide found by the Cassini spacecraft. But because the dynamical capture of Phoebe is a difficult event that is greatly assisted for a body that starts off on the same circular orbit as Saturn, it was Option 1 which Prentice selected for publication prior to the Cassini encounter (see: http://www.aas.org/publications/baas/v36n2/aas204/887.htm ).

Option 2 and 3 cover the possibility that Phoebe had originally condensed much further out in the Solar system than where it is today. Somehow (so far not explained!) it then got relocated to Saturn's orbit prior to capture. Option 2 assumes that Phoebe is a left-over planetesimal from Neptune's orbit and Option 3 that Phoebe is a 'first cousin' of the main Kuiper Belt object Quaoar. This body orbits at 1.44 times further from the Sun than Neptune.

The expected bulk chemical compositions for Options 2 and 3 were both computed on 6 July 2003 and are archived for that date on the computer file VC$3:[APM476H.GRAVI]SUN7Q.OUT;299 on the Monash University ITS Vax Cluster. The Option 2 model for Phoebe yields rock, water ice graphite and carbon dioxide ice. It has a density of 1.50 g/cc. Option 3 consists of rock, water ice, graphite, carbon dioxide ice and some 3.4%, by mass, of pure methane ice. The density for Option 3 is 1.51 g/cc.

Both Options 2 and 3 account for the carbon dioxide announced today by the Cassini Project. And both models just meet the lower limit on the observed density, which has a formal error of 0.1 g/cc.

But when Prentice posted Option 3, he noted that the relocation of Phoebe from the frigid world of Quaoar to the warm environment of Saturn would cause the subsequent loss of all surface methane ice. Since methane ice is a very light substance (density of only 0.5 g/cc), the loss of all such ice from Phoebe's chemical inventory would cause the mean density to rise from 1.5 to 1.6 g/cc. This is the very value found by Cassini!

It is unfortunate that Prentice chose Option 1 as his official pre-Cassini model. But the Option 3 model, whose existence was anticipated by his modern Laplacian model of Solar system origin one year prior to the arrival of the Cassini-Huygens spacecraft at Phoebe, accounts precisely for the two main scientific discoveries that were announced by the Cassini Project today. The modern Laplacian theory has thus clearly survived another fiery challenge! Time for a Fosters.

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FINAL SUMMARY OF ANDREW'S PHOEBE PREDICTIONS, June 20 2004

If Phoebe condensed from the proto-solar cloud at Saturn's orbital distance, prior to capture by that planet, then I predict
Phoebe's density to be 1.33 times g/cc and its chemical composition to be 37.8% rock, 59.5% water ice and 2.7% graphite.

If Phoebe first condensed at Neptune's orbit, prior to later capture by Saturn, then I predict the bulk chemical
composition to be 37.8% rock, 42.9% water ice, 4.8% graphite and 14.5% dry ice.

The expected density of this mixture is 1.50 gram per cubic centimetre.

Phoebe is a first cousin of the main Kuiper belt object Quaoar and condensed out of the very first gas ring that was shed by the proto-solar cloud at an orbital distance of 1.44 times that of Neptune's present distance from the Sun. The temperature at formation was only 28 degrees Kelvin and the gas pressure a mere 1.6 times one billionth of an atmosphere (ie 0.16 millipascals). The expected bulk chemical composition of the condensate at this orbit is rock (38.3%), water ice (32.5%), graphite (4.0%), dry ice (21.8%) and methane ice (3.4%). The mean density of this mixture is 1.51 g/cc. Relocation of Phoebe to Saturn's present distance would, however, result in the subsequent loss of all surface methane ice.

The bulk chemical compositions and densities for Options 1, 2 and 3 were all computed last year, on 6 July 2003, and are contained in the output file VC$3:[AJRP.GRAVI]SUN7Q.OUT;299 on the Monash University ITS Vax cluster. All of the above 3 options are thus based strictly on pre-Cassini analysis. They therefore provide a valid predictive base for testing the author's modern Laplacian theory of Solar system origin.

Results from the Cassini-Huygen mission will decide which, if any, of the above three predictions of the modern Laplacian theory of Solar system formation is correct. Further details of this theory may be found (in pdf format) here

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Aussie scientist says farewell to Galileo

An Australian scientist today bade farewell to the Galileo spacecraft, saying it had proven we can't be alone in the universe.

Mathematician Dr Andrew Prentice of Melbourne's Monash University said the Galileo mission had proven beyond a shadow
of doubt that there was another miniature planetary system within our own solar system.

"By extension it must be therefore that right throughout the cosmos there must be myriads of other planetary systems
just like ours. What this mission has proved is that we are not alone," he told ABC Radio.

The Galileo probe was launched in 1989 aboard the space shuttle Atlantis and proved to be one of the National Aeronautics
and Space Administration's (NASA's) most fruitful exploration missions.

It discovered the first moon of an asteroid, witnessed the impact of a comet into Jupiter and provided firm evidence of
salty oceans on three of the planet's moons. It returned more than 14,000 images.

Earlier today it concluded its 14 year exploration of Jupiter and its moons with a streaking suicide plunge into the planet's
turbulent atmosphere.

"No one knew exactly how big they were or at least how massive they were and they didn't really know what was inside them,"
he said.

"Yet according to my theory of the solar system I could see that the Galilean family of moons was like a miniature planetary
system which should have formed in the same way as the planets around the sun .

"So this gave me an opportunity to test my theory of the formation of the solar system."

Dr Prentice admitted it had not been easy to convince those who rejected his theories.

"I have had a lot of setbacks and I can assure you I do get dispirited at times and wonder whether it is worth it," he said.

"In the long term the fact that I did seize this opportunity to test the model - and it does seem to have worked out well for me
- is something I feel not only proud of myself, but I feel from the point of view of Australian science, it's nice to think that
we are able to contribute just as well as any of the others."