I have been studying the orbiting worlds of the central solar system - the Jupiter and Saturn systems - since about 1982 with keen interest. But before the Galileo reached Jupiter in 1995 there wasn't a whole lot of information available to study and I was unaware of most of what there was. Since 1995 the amount of known information has grown exponentially and the internet has made it much more accessible, allowing comprehensive pictures of some of these astounding worlds to be formed.

I have written about these worlds in Living Titan, Living Ganymede, and Complex Organic Spectral Pointers to Life on Five Solar System Worlds.

I feel that in spite of all the new data of recent years, most people have been and still are looking at these worlds through a foggy lens of preconceived ideas, and it would seem they don't care to review and update their knowledge except in a very limited way. Along the way I too have come up with ideas that have proven wrong, even ideas that look absurd in retrospect, but I have continually sought out new facts and information as it becomes available to weave into the conceptual fabric, and I forge ahead. I find that most people studying the central solar system focus rather narrowly on specific instruments and specific features without trying to fit their results into place in the broader picture with facts discovered by others, and that often the most puzzling and intriguing findings are simply glossed over without any serious attempt to figure out what they must mean.

I strive to determine scenarios that fit all the known facts, to synthesize a big picture based on reality. In the early years, I was jumping all over. I knew little and developed broad ideas, theories. Then I often found broad problems with them, and made big changes. But later on keeping my scenarios in line with new data became more and more smaller corrections, then simply occasional fine tuning. Now new info almost invariably fits right into the scenarios I've already presented, reinforces it as being correct, and adds more fascinating detail to these strange alien lands.

For some time now I've held certain clearer and more detailed conceptions of what is being or has been seen both on Titan and on all those icy airless worlds orbiting Jupiter and Saturn than I've previously presented, but I have been too busy trying to make a living and working on new inventions (wave power, plug-in hybrid electric car conversion kit for "any old car" (having accidentally invented just the motor to do it), and a new battery chemistry (since what's out there seems poor)) to consider updating my planetary works on line. However, I feel an update is overdue. I have several things to say, and besides, I wouldn't want anyone to presume by my silence that I have in any way recanted of my scientific "heresies".

Rather than try to edit and update Living Titan and Living Ganymede at this time, I'll just do this "addendum" web page to update and clarify the views of the fascinating spheres of the central solar system. Someday I may update my earlier works with this new info, but if I never get around to it, here it is!

Clearly, Titan's tropical dunes are submerged in liquid methane and the peaks are almost level with the swampy sea surface. Unlike Earthly dunes, the dune features have the same appearance regardless of radar viewing angle. Cassini's SAR radar pulses penetrate methane well but not indefinitely, so the peaks rising to near the surface are lighter than the much deeper bottoms. In the visual images, the dunes are much less apparent than by radar, often being entirely invisible, because the camera doesn't penetrate the sea surface very well from space.

Patches of vegetation sticking out of the liquid methane, mostly at the dune peaks, give the dune features very high contrast in patchy areas in the radar images and show the dunes in some visual images. The dunes resemble the tiny sand ripples seen on Earthly beaches anywhere that result from wave action. The vast difference in size is the result of the difference in wave period. Whereas the small waves making sand ripples on Earth go in and out every few seconds, Titan's east-west tidal flush runs over a period of sixteen Earth days. Thus, sand ripples a few inches between peaks become vast dunes with kilometers between peaks.

Here is a clearer appreciation of the nature of the area where Huygens landed, first written of on May 9th 2008:

It would appear that Huygens descended through the methane drizzle over an area of sea with no real dry land anywhere, just a typical Titan tropical "tidal wetlands" area of irregular sea dunes stretching off into the distance in all directions, whose crests create patterns of vegetation visible on and above the surface in the images.

And it would seem that Huygens' "creme brulee" soft landing, seemingly likely to have been a double "sploosh-splat" through a bit of methane before the soft ground, was right on top of a small dune crest, approximately level with the sea surface. (I pinpointed the spot a couple of years ago in a 'closest view' downward looking mosaic, shown in Living Titan chapter 4. It's a closer-in view than anyone else has ever done AFAIK.) (BTW the penetrometer may have pierced a leaf or stem.)

Some say there's a couple of inches of clear liquid visible moving about on the surface. It was seen independently by at least two other writers well before I noticed it. Some say they don't see it. Some scientists recognize "changes" between after landing image frames but can't say what they are. The methane RH (50%) was too low for a "ground fog" as first suggested in explanation by some. With liquid methane having a lower refractive index than water, there's less visual difference between "submerged" and "in air" than on Earth. The GCMS found "relatively pure liquid methane on the surface". Some say that's just "saturated soil", but "saturation" still indicates liquid methane. Some have said Huygens' SSP instruments preclude liquid (GCMS notwithstanding). I inspected the raw SSP readings myself and I found that while the accelerometer data strongly supports liquid, and while other SSP info showed for sure Huygens was at rest and not floating, some of the other SSP instrument readings made little sense for any plausible surface, and should hardly have been used to support far reaching, definitive conclusions of any kind.

But it hardly matters whether Huygens bottomed in two inches of liquid or if the saturated dune surface was right at the 'water'line. The dune is there, and Huygens obviously came down right on it, for better or worse. If it had missed, 30 meters one way or the other to the dune sides, it would almost surely have bobbed around and taken some more diverse panoramas, instead of grounding and taking all those after landing images of the same scene.
 

In March 2008, it was disclosed that Titan's rotation evidently isn't quite synchronous: its features were seen to be gradually working their way westwards. From publications:

"Using data from the radar's early observations, the scientists and radar engineers established the locations of 50 unique landmarks on Titan's surface. They then searched for these same lakes, canyons and mountains in the reams of data returned by Cassini in its later flybys of Titan. They found prominent surface features had shifted
from their expected positions by up to 30 Km (19 miles)."

and

"The scientists found that they could match the positions if they tilted the rotation axis slightly and sped up the rotation by 0.36 degrees per year."

Evidently Titan is turning just a bit faster than equilibrium synchrony - very slowly as regards normal "rotation" of a sphere, but very rapidly geologically speaking.

In Chapter 3 of Living Titan I detailed a theory that explains the broad layout of Titan's surface features, but I was unable to figure out why they are all shifted around 20 degrees of longitude eastwards of where the tidal forces logically indicate they ought to be. Gradual rotation explains it. As Titan's surface gradually shifts westwards relative to Saturn, the "duney" liquid methane "swamplands" and bright surface features in the equatorial regions, formed by the tides, creep along to stay at the tidal nodes, but they naturally lag behind. The observed 20 degrees eastward of "equilibrium" longitudes would seem to be a reasonable amount.

Why would Titan rotate other than synchronously?

The dry, airless worlds rotate synchronously. But Titan isn't dry, and it has an elliptical orbit. The skew of the tidal features indicates that the rotation is continual. The tidal flows of the equatorial sea must be largely responsible for the gradual "extra" rotation. Somehow, the forces of rotation don't balance to null for the solid body. This much is clear.

The details I'm a bit more hazy on, but I'll take a stab at explaining them. As it approaches Saturn and periapsis, the surface liquid becomes slightly more ovoid than Titan's overall shape, 9(?) meter high tides being raised at the sub-Saturn and anti-Saturn points. This additional ellipticalness gives Titan more tidal drag when it's closer to Saturn than when it's farther away. And, the deeper liquid can be shifted with less friction. At periapsis, Titan is moving fastest and thus rotating "too slowly" for its speed in synchronous terms. In the lower end of the orbit, Saturn tries to pull the high tide point 60 kilometers eastward, which tug tends to speed Titan's rotation.

In the upper part of the orbit, when Titan is moving more slowly and hence rotating "too quickly" for its speed, although Saturn is pulling liquid westward again and would like to slow Titan's rotation back towards synchrony, the high tides have subsided and there's more fluid friction: the pull on the liquid doesn't bring it back west as far as it went east. Thus the equatorial liquid probably slowly circulates eastwards around Titan, equally and oppositely (by force required) to the westward motion of the ground. Also, being more spherical, Titan has less tendency to be slowed than it had to be speeded up in the lower reaches.

Here's a prediction: Look for equatorial features even on large scales to continue to change and evolve quite rapidly over time. Most of them may bear little resemblance to today's in a few years or a few decades. Indeed, the SSI visual images of the tropics taken to date appear to show most small scale features have changed between flybys. The fact that the tropical surface features change in images on every subsequent Cassini pass probably explains the conception by the imaging team that (paraphrasing) "Titan's hazy atmosphere means the images are only accurate down to a level of several pixels." Last I looked, which is some months ago now, there were still no good "close-up" visual images of dry land areas, where the features might be expected to "sit still" between passes, so the misperception, if such it is, doesn't get tested.

An interesting aspect of this whole rotation process is that the very broadest scale equatorial features appear not to move. As the surface and the Saturn and anti-Saturn tidal nodes creep to the west, the equatorial wetlands, shaped by the tides, seep westwards to stay with them. Thus from distant Earth, we observe vague dark and light patches that appear to remain stationary, giving the impression that Titan always keeps one face to Saturn as expected, whereas it seems that it actually very gradually rotates.

I've probably written about this, but it is obvious that the land areas of Titan are covered with forests. For example, I gave the "Kissing Lakes" image to a government cartographic team leader who views Earth images from various sources daily, and, without telling him it wasn't Earth, simply asked him what he thought of it. He went into various terrain details, noting the flattish landscape (that describes much of Titan), likely surface runoff flow paths, and along with the rest said, without reservation and making no special point of it, that the lakes were surrounded by "mixed forest". He also mentioned vegetation seemed to be growing in the lake, but as that much aquatic vegetation would be more unusual on Earth, he was more guarded and said "but it could be radar noise". (He also took a couple of guesses of which Earth satellite had made the image, and made estimates of the image scale that would have been about right for Earth - but Titan trees are much larger than Earth trees, in the light gravity and gentle winds.) One need only look downwards at Earth with Google Earth to see countless similar textures, albeit usually criss-crossed by human works. It is beyond my comprehension that no one else has pointed this out.

At one time, I thought Callisto had to be the world where the airless life originated. Later I thought it had to be Ganymede. To be honest, I really am not sure at this point which one it is. The animal - and human - life is probably confined to its sphere of origin. But it's clear from spectrographic readings of the same chemistry and visual images that the vegetation of this life has spread throughout the Jupiter and Saturn systems onto all the airless worlds wherever there is good soil that doesn't get irradiated by the deadly ion bombardment carried by Jupiter's and Saturn's magnetic fields.
 Ganymede has its own magnetic field, and Callisto has a conductive liquid layer that results in an equal and opposite field induced by Jupiter's field. Evidently that cancels Jupiter's field and deflects the ion bombardment. So these spheres are probably both protected.

On the small wholly solid spheres orbiting Saturn, however, there is no protection. The ions sweep the trailing halves of these orbiting worlds from behind but leave the front faces untouched. Hence we see on Iapetus a leading hemisphere covered with the dark, fluffy organic matter, while the trailing hemisphere is mostly bright icy bare soil. But the ions, being charged particles, veer like lightning to hit the nearest high ground, leaving certain sheltered crevasses, valleys and areas of crater floors free of this radiation. The one-to-one correspondence of dark areas to what look like likely ion free locales appears to graphically illustrate the point.

BTW, the term "fluffy" for the surfaces ("very fluffy" for Iapetus) comes from those who've studied the diurnal temperature readings, as being the word most descriptive of what would cause the temperatures to behave as they do, and it's also been disclosed that sunlight must penetrate the thin fluffy layer. What else but vegetation: stems, leaves and branches? I've tried to imagine types of dark, fluffy, organic "dead geology" surfaces to fit the facts, that might have naturally arisen, without coming up with anything plausible.
 

Even tiny Hyperion has dark crater floors, evidence that the vegetation spreads like weeds through space, and it grows on even such a tiny body, there in these peculiarly protected locales. It has long been a theory of mine that one method of plant propagation of airless world plants is that they would shoot out seeds or clusters of seeds. Once established on any very small sphere, these would shoot off into space and spread to all nearby worlds. Indeed, although I wasn't expecting anything visible except close up, there are bright streaks in many of the "closest" view Iapetus images that may (or may not) be more than cosmic rays.

We also see that this vegetation grows far more densely on the outermost worlds of each system, especially Callisto and Iapetus. The nature of the soils is quite different. Iapetus and Callisto froze over at early dates, and meteors and comets added whatever elements they brought to the surface soil, while also breaking up rock into soil, as illustrated by the gritty soil of Earth's moon. The inner worlds nearer Jupiter and Saturn are tidally heated, keeping the water liquid for ages. On airless worlds, the soil is even more vital because with no air, every nutrient is derived from it. Even now Europa and perhaps tiny Enceladus have liquid water. When a good sized meteor strikes Europa, it breaks through the "crust" into the liquid beneath, leaving a rock solid surface of rather pure water ice. Nothing could grow in - or should I say on - that! Ganymede is intermediate, with some areas of undisturbed soils being much richer than others where the interior was churned up earlier in Ganymede's history. Many of its grooved areas disclose bright icy crests with very dark "troughs" between them, doubtless filled with the fluffy complex organic matter, vegetation.

 I initially wondered how life that originated in the Jupiter system could live and grow almost twice as far from the sun in Saturn system, but readings disclose that the temperatures on Iapetus at midday are only ten degrees (C, K) cooler than on Ganymede. At night it is much colder, but that's not when plants are active. Could this vegetation also live even farther out... like on the moons of Uranus? Frankly, it must be so cold out there even in broad daylight I doubt it, without even looking up temperature readings that are probably available. Only a space probe could tell for sure, but I'd much rather see Ganymede and Callisto orbiters first to get close up to where we've already found life.

And why are the organic areas simply "dark"? It's only because most of our images of them are monochrome. In the frustratingly sparse color coverage, the dark areas of Callisto, Ganymede and Iapetus are shown to be greens and browns, surprisingly similar in color to Earthly vegetation in spite of the obviously vast chemistry differences. The closest images of Iapetus' front side appear bright green, both in natural color and with infra-red "green".

All the airless icy worlds have some very strange features. Seeing life in the spectrographic readings, I mistook these bright extrusions for being plant stems - what else could be long and thin and spread here, there and everywhere?

Of course, ice is a major type of rock on these colder spheres, but ice has an unusual feature that Earthly rocks don't have: it expands as it freezes.

When a large meteor strikes, it blasts out a crater in the surface. The heat energy generated by the impact melts the ice grain soil within the crater. And not just the top inch, but say perhaps as deep as 1/4 or 1/3 of the crater's diameter, so there's a deep pool of water.

In the vacuum, the surface of the water starts to vaporize, which cools it rapidly. The surface freezes over very quickly, leaving the pool of still warm water trapped under the ice.

There's no continuing heat after the impact, so the water underneath starts to freeze, probably from the top down, and it expands as it freezes, unlike most other materials. The pool now has a solid cover and it's expanding.

So at this point, it starts to "raise the roof" all across the crater. The crater including the inside walls of the rim is now solid ice. The water is bound to break through and form extrusions. On different worlds, this may take different forms.

On the inner worlds where tidal action has churned everything up, the surface is largely composed of glare ice. This can crack anywhere, often in the center of the crater or the rim, and the water forces its way out like toothpaste squeezed from a tube. These stick out at odd angles or break off into cylindrical sections.

On Callisto, Iapetus and parts of Ganymede, the soil around the crater is loose grains. The liquid water comes oozing upward more gently, out of the gaps all around the crater rim. The surface freezes and forms a "skin" as it emerges, but more water beneath still pushes upwards as the pool freezes, "growing" the tall thin bright things all around the rim of the crater. In the light gravity, only very large ones such as in the Asgard compression ring oozings bend over before they freeze up. But all the worlds have many widely varying ice extrusion features.

Here is a theory on the formation of the "Walnut Ridge" or "Cassini Regio" on Iapetus. It probably formed in a similar way, except that it probably occurred as a result of a huge meteor strike very early in Iapetus' history when it was still growing rapidly and, being constantly bombarded by meteors and comets, it was still molten inside. This meteor struck elsewhere than the ridge, perhaps antipodally, perhaps at 90 degrees to it, and the added matter of the meteor expanded the entire crust and caused a huge fissure to open up. The water expelled through this fissure formed giant ice extrusions all along what became the ridge. Subsequent meteor and comet hits wore this down and added their own substance, giving the huge structure the "hilly" sloping sides it now has. The cooling interior solidified and together with light gravity ensured the ridge wouldn't subside.

Whatever the original orientation or rotation of Iapetus, the tall center of ridge became the long axis and so as the rotation (if any) slowed, the heaviest part of the ridge was bound to face either directly away from Saturn or directly towards it as it does, and the ridge, forming the second longest axis, naturally became the equator. (Saturn bulges at the equator and so its moons' second longest axes also gravitationally line up in this direction.)
 

The worlds orbiting Saturn have essentially circular orbits except for these three. Normally, tidal forces gradually circularize satellite orbits, and for these to not have them indicates there are forces keeping them eccentric. It would take a long time for Saturn to circularize a world's orbit, so even small forces consistently counteracting those tides could keep them eccentric.

Tiny Hyperion makes almost exactly three orbits for every four of Titan. The 1% difference to this ratio would seem to be due to precession, and it is commonly accepted that the two orbits are tidally locked, synchronized, and that Hyperion's orbital eccentricity is derived from gravitational interaction with Titan. Titan and Hyperion pass each other just once every four Titan orbits on exactly the same side of Saturn (minus 1% precession) each time. This accounts for Hyperion's eccentricity. However, it is being said that Hyperion is too small for its gravity to account for Titan's orbital eccentricity. Surely another factor is at work.

One possible factor is that Hyperion's rotation changes. Normally the long axis of this potato shaped world points at Saturn, but when it is closest to Titan, it swings around to point at Titan. It "tumbles erratically". Hyperion is small but not weightless, and to pivot its entire mass must take considerable energy.

Also, Hyperion would lightly pull liquid methane westward across Titan's surface as they pass, which would expend energy both coming and going. Perhaps all together it's enough to account for Titan's orbital eccentricity. (Titan also rotates, gradually creeping westwards, but Hyperion is probably pulling in the wrong direction to be assisting that.) I haven't seen any references to these rotational or fluid frictional forces or the energy that would be required, so as far as I know, no one has taken it into consideration. It would seem the relationship between Titan and Hyperion deserves more scrutiny.

Another possible factor is that Iapetus - the only other Saturnian world with a markedly eccentric orbit - is within about 5% of having one orbit per five of Titan (or four orbits per twenty of Titan), and four orbits per fifteen of Hyperion. If it wasn't for the 1% and 5%, all three bodies would line up again and again at the same point in their orbits every twenty Titan orbits, and at no other point would all three line up. Thus, this point would become Titan's apoapsis and Iapetus' periapsis.

Iapetus is a small world that orbits Saturn considerably farther out than Titan and Hyperion, and it has been said that Iapetus' orbit is not synchronized with Titan's because precession doesn't account for the 5% difference.  Nevertheless I suspect we may be missing something: that the three worlds are likely all tidally synchronized somehow and account for each others' orbital eccentricities. If that is the case, tiny Hyperion must act partly as a "catalyst" between Titan and Iapetus in some variant of the repeating three body lineup.

(
 Updates: Minor wording and spelling edit August 15th 2008.
)