Are Saturn’s Rings Evolving?
The Cassini spacecraft continues to astound scientists and the public with its pictures from the Saturn system. New discoveries have been made about the rings and small moons embedded within them. At times, it appears that destructive processes are at work. Some scientists, though, see them evolving. Can ring particles grow into moons? And is that how planets grew from rings around stars?
Readers might first enjoy this closest-ever look at Daphnis, a small moon that orbits in the Keeler Gap in the rings, published Tuesday. Hints of a crater can be seen on this little 5-mile object, and the scallops and gouges it creates as it passes the ring edges are obvious (see second photo and Space.com article).
Other moonlets have been found embedded within the rings. Though too small to see, they can be detected indirectly by propeller-shaped wakes they leave. Perturbations closer to Saturn move faster; those outside move slower. The two oppositely-directed wakes create the propeller shape. Some of these had been detected in 2006. There may be millions of these large ring particles that are big enough to create the propeller structures, but too small to clear a gap in the rings. Now, about a dozen of the largest ones, one estimated half a mile in diameter, have been tracked for as long as four years. The Cassini team issued a press release about them. It was picked up by Space.com and Science Daily. Some of them launch material a half mile out of the ring plane; others have been seen to change orbits over time, perhaps by being bumped around in the rings, or because of the influence of passing large moons. In a way, these observations fulfill expectations from Voyager days in the 1980s that rings might contain embedded moons that act either as sources or sinks for ring particles (e.g., NASA 1981, Harvard 1980).
Because these observations represent the first time that embedded objects in a dust disk have been tracked, scientists are getting excited about the possibility of learning whether they can grow or “accrete” into larger objects like moons – and whether the same principles might apply to the growth of planets from dust disks around stars. Indeed, last month Space.com and PhysOrg joined in JPL’s suggestion that some of the small moons outside were born from ring particles. Their low density and saucer shapes, combined with young ages (estimated less than 10 million years based on freshness of the surface) led scientists to propose that moons are still forming today. But are moons grinding down, or winding up? The Cassini press release cautiously made an argument for the latter. Though the press release headline stated that the propeller objects “reflect solar system origins,” it only suggested that the processes observed at Saturn “gives scientists an opportunity to time-travel back into the history of our solar system to reveal clues about disks around other stars in our universe that are too far away to observe directly.” Imaging team lead Carolyn Porco was more confident. She claimed that “Observing the motions of these disk-embedded objects provides a rare opportunity to gauge how the planets grew from, and interacted with, the disk of material surrounding the early sun.”
Not all is well in theories of planet formation, though. Astrobiology Magazine complained this week that many of the exoplanets discovered around other stars do not fit theories of the origin of the solar system. “Over the past two hundred years, a standard model emerged to explain how solar systems form,” it began (that model began with the “Nebular Hypothesis” by Laplace in 1796). “Using our own solar system as a guide, the model explains the existence of a central star (our Sun), an inner system of rocky, ‘terrestrial’ planets, and an outer system of ‘gas giant’ planets, all orbiting in nearly the same plane of rotation as the central star.” It worked out well when there was only one system to study (ours). Unfortunately for modelers, “Recent discoveries of planetary systems around other stars have challenged this model. These exoplanet discoveries have included gas giant planets in close orbit around their stars, some of which are in radically different planes of rotation from their primary stars.”
Modelers have come up with “Various schemes suggested to explain how a gas giant could form beyond the ice line and then move inward toward the star,” the article continued. But is giving this necessity a name like “migration” sufficient to qualify as an explanation? Perhaps transfer of angular momentum from the disk would make a gas giant start spiraling in, but how could it get kicked into a high-inclination orbit? The ad hoc addition of a passing star might kick a giant planet out of the plane, or even make it revolve backward. “There are a lot of things going on that we didn’t anticipate,” one modeler remarked.
A downside of all this chaotic interaction and migration is that it makes life less probable around other stars. Systems with gas giants moving wildly would easily kick habitable planets out to oblivion. Aside from that concern, another researcher was dubious about whether adding passing stars and migrations improves our understanding of planet formation. “I have a hard time believing that improbable events like this could lead to a large percentage of planets in retrograde orbits,” he said. It seems a little premature, therefore, to think that small-scale processes in Saturn’s rings will shed light on where our “relatively peaceful” solar system came from.
He would probably be even more incredulous after reading Jonathan Henry’s article in the latest Journal of Creation from CMI (24:2, August 2010, pp. 87-94). Dr. Henry shows from Laplace to the present that “Solar system formation by accretion has no observational evidence.” Accretion has never been shown to work in any realistic lab experiment. Particles do not accrete into planets: they bounce off one another or break into smaller pieces. Furthermore, there is no evidence of nebula collapse, of stars forming, or of planetary systems forming. There is much evidence for disruption, destruction, and dissolution, but not the accretion of small objects into bigger ones.
Henry reminds modern readers that 19th-century modelers found a coincidental spacing of the planets that fit a mathematical formula, and called it “Bode’s Law.” In the absence of supporting evidence, some thought that this spacing constituted a “law of nature” that other extrasolar systems would have to obey. Well, they didn’t. Hot Jupiters and renegade orbits abound, and as Astrobiology Magazine admitted, our solar system “may be something of an exception.” Over and over, Henry shows that the easy, observation-deprived speculations of Laplace and others have fallen under the merciless onslaughts of observations. As early as 1859, James Clerk Maxwell showed, based on his model of Saturn’s rings, that larger particles cannot coagulate from revolving small particles – a blow to the Nebular Hypothesis as well.
Modelers keep trying to escape the empirical evidence by inventing ad-hoc elements to their models – migration, disk instability, and other heuristic suggestions to try to maintain their bottom-up, evolutionary world view. But alas, “Accretion theory and the nebular hypothesis… require conditions that natural law has not been shown to be capable of providing, such as artificially low collision velocities between accreting particles,” Henry ended. “Outside of scientific discussion, such physically impossible conditions are called miracles, implying that the origin of the heavenly bodies was a supernatural event, the claim the Bible makes.”
So if you must believe in miracles anyway, why not choose the ones that were designed for a purpose? You might find that thought – purpose, design – propelling you to new heights of joy and appreciation for being able to read this article in the calm, pleasant air of a Privileged Planet – one that not only meets our physical needs, but provides us a platform from which to make scientific discoveries about Saturn, stars, and the whole universe.