by Craig Carmichael (independent researcher) May 2007
 
 

There seem to be five worlds in our solar system whose surface has been reported as being abundantly covered with complex organic "tholins" compounds:

It was a surprise that the Galileo found tholins on Ganymede and Callisto - unexpected and unpredicted. Others have supposed that they should also be present on Europa, yet there is no sign of them there. Some of the tholin compounds have not been identified. Having found tholins on Ganymede and Callisto, scientists were not so surprised when they were also found on Saturn's moon Iapetus. Still, they are unexplained. Several worlds show simpler organic molecules. There are organic readings on Saturn's odd moonlet Phoebe, but these differ spectrographically and I expect they are probably fairly simple molecules.It seems improbable to me that these complex and doubtless fragile compounds should have persisted on planetary surfaces through their meteoric accretion stages with the attendant heating and geological morphology, even if they had existed in cometary material supposed to be "abundant in the solar nebula". I propose that, as on Earth, it is living organisms that form complex organic compounds. It seems to me life is the obvious and simple interpretation of the spectralfindings.

There is more evidence:

Analysis of spectral data from the Voyager probes found that the temperature profiles of Ganymede and Callisto were best explained by a two-layer surface with the top layer having a very low thermal inertia^{[1]. This would seem consistent with a covering of vegetation over the ground.}

^{On Iapetus, "the dark material appears to lie on top of other geologic features seen on Iapetus thus far, implying that the event which formed the dark coating occurred later in Iapetus' history."[2] Again, this and the idea that the dark material is "a relatively thin layer"[2] is consistent with vegetation on the surface.}

^{On Titan, the tholins found are said to be "the building blocks of life", and compounds such as ammonia, found on the surface but not in the atmosphere, are thought to be "the end products of a complex organic chemistry". There is "an unidentified blue slope in the near infrared". If life on Titan seems incredible, is it not even more incredible that, in the absence of life, there should be complex and unidentified organic compounds "unique in the solar system", and complex organic chemical reactions occurring on the surface? Cassini and Huygens findings indicate no UV or other energetic radiation, lightning hasn't been detected, and there are low wind speeds and gentle conditions. What but life would stir the elements to these unique organizing activities?}

^{Interpretation of spectrographic results as being indicative of life is not without support from the imaging. Scrutiny of the nearest images from both Ganymede and Titan indicate, at least to some viewers, that they both appear to be covered with vegetation. It's not very clear, but it is as clear as the space probes sent could be expected to show such things. It would doubtless be much more clear (or else counterindicated) if any of the closest images had been taken in color, but unfortunately, neither Galileo, Cassini nor Huygens was (is) capable of taking color images of nearby planetary surfaces. The best views of vegetation on Ganymede are the images of regions 30 - 45 degrees north latitude at about 50 meters per pixel, taken obliquely from Galileo passing by over the equator. Finer scale views of Titan, especially the Cassini SAR RADAR images and the Huygens images, appear to disclose lush vegetation both on land and in the liquid methane.On both Ganymede and Titan, the scale of the vegetation is gigantic compared to Earth, allowing us to see it even from space and making it hard to believe. If there were large scale human works such as Earth's cities on Ganymede or Titan, they should have been seen, so we may infer that there are no advanced civilizations comparable to Earth's on these worlds. Animal life, unless seen by the Huygens probe after landing or unless incredibly huge, should definitely have been too small to image with any certainty of identification, so the presence or status of animal life, and human life, on either sphere is, predictably, undetermined.}

^{Why should we be surprised by giant vegetation on low gravity worlds? The theoretical limit to tree height on Earth has been calculated as being 120 meters, and the tallest actual trees are about 140 meters. This is related to the ability of plant cells to push sap from the base of the tree to the top against gravity by cellular capillary action. Ganymede and Titan both have 1/7th of Earth's gravity. All else being equal (for purposes of gross estimation), one might expect trees could grow 7 times as tall, or 120 * 7 = 840 meters. One thing that's not equal on Titan is that the liquid is methane, density .8, instead of water, 1.0, so it's lighter to push up the stalk: 840 meters / .8 = 1050 meters. That's trees a kilometer tall, and it's why forest canopies are visible on Titan in radar images from space even at 30 meters per pixel rez, and why individual branches and tree trunks (the "poles") can be discerned on Ganymede. Something that throws a wild card into vegetation heights on Ganymede is that in a vacuum there really ought to be no liquids. The vegetation must either create its own internal pressure to where liquid can exist, or else Ganymedean "sap" is a gas going up the stalks. Obviously, gas could be pushed up any conceivable height of stalk and wouldn't be the limiting height factor. A thick skin that holds in gas or liquid could perhaps account for the 'gelatinous', 'globby' appearance of certain forms of Ganymedean vegetation.Callisto discloses no plant forms large enough to be discerned in the closest Galileo probe images. However, its entire surface besides icy slopes and other bare ice areas appears to have a "blanket" which obscures smaller surface features, and which has been variously described as "dark", "gritty" and "fluffy". Indeed it looks so little geological that an electrostatic charge holding "grit" aloft has been proposed (seems absurd - whence cometh this charge?), as well as sublimation of ice from flatter areas, leaving the darker material. (and why, and where does the ice sublimate to?) Whatever it is, this happens also to be the appearance one would expect from dense vegetation too small to image. Iapetus has only been imaged at many hundreds of meters per pixel, and there are no plans to view it from close enough to certainly discern even very huge plants.}

^{Colorized version of Galileo image of Ganymede. (@2x)
(Image #359946139, 35 degrees North, 186 degrees West, 45 x 73 meters per pixel, imaged from Galileo, flying over the equator. This geometry has provided a fine perspective view.)
The colorizations, while they doubtless misinterpret some of the forms and details, highlight many amazing image features people appear to have paid little attention to. Some other interesting features are not colored. On inspection, the majority of the short vertical lines do not appear to be image artifacts. What are they if not trees?}
 
 

^{3. Migration and Distribution of Ganymedean Life}

^{Why these worlds, and no others? It is my belief that the life which seems to exist according by the spectral readings on Callisto and Iapetus, originated on Ganymede. Meteors occasionally spew up debris including seeds, spores or living roots from Ganymede's surface. Some exceed Ganymede's escape velocity and some (evidently) eventually fell onto other acceptable airless worlds and grew.So, why should Ganymedean life flourish on two other worlds but no others? It isn't hard to start eliminating worlds as possibilities. Io is so hostile to life it can be immediately dismissed. (No human will ever go near it!) Likewise, anything that hit Europa would soon die of radiation poisoning if it didn't en route. The same might perhaps apply to Saturn's small inner moons (Rhea, Dione and Tethys) as well as Mars (unfiltered UV there). Mars is also probably too hot and has an atmosphere that may well be inimical to Ganymedean life (and would fry it during landing). Dione and Tethys may be simply too small. (I thought Iapetus would have been too, and also that the Saturn environs would have been too far from the sun for Ganymedean life... but the Iapetus spectral readings are there.) An alternative reason nothing is found on Rhea may be simply that nothing from Ganymede has ever landed alive on its leading hemisphere. Or, its geology may provide little but hard ice for soil. Jupiter's magnetic field sends charged particles bombing into the trailing hemispheres of its satellites, but Ganymede has its own magnetic field to deflect these. Callisto has a weak and varying magnetic field that is electromagnetically induced by Jupiter's field in liquid water deep under the crust. This is protection of a sort but not very good protection, so Callisto's trailing hemisphere is somewhat unfriendly to life and a lower density of tholins is seen there than on the front half. Iapetus is much too small to have any magnetic field, so its trailing hemisphere is freely bombarded by Saturn's magnetic field, making it relatively uninhabitable to life, while the leading hemisphere has grown dark with migrated Ganymedean plants, which could, perhaps, in Iapetus's 1/40th gravity, possibly grow very huge indeed.}

^{Earth of course has its own magnetic and other protections from the energies of space, and no doubt atmospheric Titan has its own shields -- some have been identified. For example, elements of its upper atmosphere reflect UV rays back the way they came!}
 

^{Since on Iapetus the dark "life area" geography is well defined and there are images of it, here is some detail. The same could perhaps be done for Ganymede (presumably showing latitude differences only) and Callisto (latitudes and longitudes) if there are images and if the regions are defined well enough.}

First let me say the idea that Iapetus's dark coating came from material blasted off the distant moonlet Phoebe has so many flaws that in the interests of brevity I won't discuss it. It is just one of a number of impossible ideas that attempt to explain the images of life on these various worlds in terms of non-living phenomena.

^{The boundaries of Iapetus's dark area and the constancy of the darkness within that area are relatively convincing as describing the region where vegetation seems plausible. It is distributed throughout the lower latitudes without notable gaps, and comes to faily well defined northern and southern limits at 45 to 50 degree latitudes:}

^{And it ceases on the trailing face, exposed to Saturn's magnetosphere, first in the temperate regions, and more gradually in the tropics in a semicircular shape, at both ends. I suppose it doesn't end very suddenly because Iapetus essentially orbits beyond Saturn's field except when it passes through the magnetotail. Iapetus thus only receives very modest doses of ionic radiation compared to Saturn's inner moons:}

^{Especially at its eastern extremity near the equator (facing Saturn), vegetation appears to spread a fair ways onto the trailing hemisphere within what I presume are sloped areas somewhat sheltered from the magnetosphere's ionic particle impacts. One sees a somewhat dark ring in an impact basin, "the moat", on the right above as being relatively flat and dark; a higher resolution image gives the possible impression of steep terrain with smaller dark areas sheltered westward of various hills and scarps. But it is difficult to tell shadows from darker terrain in monochrome images of Iapetus.}

^{There is an excellent color image (PIA06167) in which shadows are quite distinct from terrain brightness.  Though it doesn't extend across an east-west boundary, in this small excerpt the dark brown coating can be seen to gradually thin to light grey towards the north pole. Again appropriate to the vegetation model, northern walls of craters, facing south and thus simulating lower latitudes in small selected areas, have the dark coating. Some whispy darker streaks of higher latitudes also appear to disclose southerly oriented slopes.}

^{4. Conclusions and Forecast}

^{2. http://ciclops.org/view.php?id=708}