Life seems to be everywhere on Titan. Titan, with its liquid seas, tides, Earth pressure atmosphere and similar polar tilt, is amazingly like the Earth in some ways, but not in ways that would make it a comfortable place for Earth people. Not only is there 1/7 gravity and a very long day (16 Earth days) and very long seasons (the year is 30 Earth years), but the temperature (94 ºK, -279 ºC) and hence the chemistry is vastly different. With seas of liquid methane, it is likely that plants regenerate methane themselves much as plants here regenerate oxygen. Titanian vegetation seems to attain a scale that is probably best explained by the low gravity and the need to flourish in strong tides. It has many similarities to Earth plants, but a possible major functional difference as well. I wish to speculate on the nature and biochemistry of Titanian life, but first let's have a look at the meat of the matter: what Huygens has actually shown us!

Huygens Instrument Readings Indicating Titanian Life

(Feb 5 2006)

In December 2005, results of the Huygens spectrographic findings were published in Nature. Having observed vegetation ubiquitous in the images, I was expecting to hear of "complex organic compounds" on the surface, without knowing just what these might be, and the reports didn't disappoint me. The synopsis was:

"The infrared reflectance spectrum measured for the surface is unlike any other in the Solar System; there is a red slope in the optical range that is consistent with an organic material such as tholins, and absorption from water ice is seen. However, a blue slope in the near-infrared suggests another, unknown constituent."

The "tholins" finding does indicate complex organics. Going into more detail:

"The four major characteristics of the surface spectrum are: (1) a relatively low albedo, peaking around 0.18 at 830 nm; (2) a red slope in the visible range; (3) a quasilinear decrease of the reflectivity by a factor of about two between 830 and 1,420 nm; and (4) a broad absorption, by ~30% of the local continuum, apparently centred near 1,540nm (although its behaviour beyond 1,600nm is poorly constrained) as seen in Fig. 15b. This spectrum is very unusual and has no known equivalent on any other object in the Solar System."

Item one says it's a dark color, reflecting at the most, 18% of sunlight, and that the brightest color is in a near infra-red wavelength. Item four says Titan's surface is unique and mysterious. Of specific interest:

"... a featureless blue slope is not matched by any combination of laboratory spectra of ices and complex organics, including various types of tholins. Depending on their composition and structural state (for example, abundance, extension and/or clustering of sp2 carbon bonds), organic materials in the near-infrared exhibit either distinct absorption bands (for example, bright yellow-orange tholins), or a feature-poor red slope (for medium to low-albedo organics), or a very dark and flat spectrum."

It was also said that the brighter "terrain" showed more redder than the darker, from which I tentatively infer, along with the blue, that the leaves and-or soil are a purplish color, with the sea liquid more of a green. The final note on the blue slope was:

"Assessing the material responsible for the blue slope is a major challenge and also a prerequisite for a secure identification of the 1,540nm band."

The content of Huygens's images of Titan is breathtaking, even though the quality leaves much to be desired.

Nobody, myself included, expected to actually see life there in the Huygens images. That Titan might have life was almost inconceivable. If it did, it would be algae and microbes Huygens wouldn't be able to see. But there they were in the descent images... something that looked like the head of a seal, sticking out of the water!... something perhaps swimming!... a squid!... a giant newt on the bottom!... and vague forms that didn't look geological, here and there!... something quite mysterious in the water! And even more astonishing, areas of land that appeared to be organized in some way! These are the signs of Titanian life Huygens has given us a glimpse of.

Much of what I saw, though, was pretty mysterious until I finally realized the main feature of the landscape: aquatic plants! In retrospect, it is far more likely in random shots of a world that one will capture the images of vegetation, which should be "everywhere" and may be very large, than catch a fleeting glimpse of relatively small and probably sparse animal life. Vegetation is what anyone searching planetary images should be seeking in a quest for life. (That seems so obvious now... It took me two worlds, Titan and Ganymede, to figure it out! Now, where else might one apply that hard-earned knowledge in this solar system... hum ta tum!) Four images of what looked to me like a gigantic newt with a sail on its back under the sea got me looking seriously at the Huygens images for more Titan life until I broke the perceptual barrier and recognized vegetation.

We all want better, and color, pictures, but we don't have them and we won't for some considerable time. It is up to the viewer to decide whether it is more believable that so many things are illusions that just mimic vegetative forms, or whether they actual plants, and whether rather distant views of land that seems to have vegetation are just that, or flukes of the Titanian landscape, light and shadow. I present them here as if they are what they appear to be, as much as I've been able to make sense of them. Making sense of Titan's plant life has taken some time and I can't claim to have all the answers. While the scale of Titanian vegetation boggles the mind, pause to consider that here on Earth, it is said that a single rye plant can spread up to 400 miles of roots underground and many other examples of kilometric plant root and fungus lengths can be cited.

Vague, murky shapes in the sea, from 25 Km up. How could so many bizarre things huddle together in one place? They appear to be giant aquatic plants! We see huge stems, branches, leaves, and perhaps even some roots. (The "bubbles" are on the camera lens. The light colored band at the top is also a camera trick.) The tidal flow runs East - West through Huygens' channel. The lighter colored areas are likely mats of leaves, or surface reflections, rather than shallower 'water'.
Scale is about 3-1/2 Km left to right; South is towards the top; land is not far below the "bent arrow" feature and the bottom of the image, shallower 'water' perhaps explaining the lighter shade at the bottom. The colorized image attempts to show the real forms in the original image but contains much "artistic licence" as fine points of detail in the Huygens images are often distorted and unclear. The true colors are of course unknown.
 
 

Here we follow the plants down in altitude, obtaining different views of them. Again, various leaves and stems are in view. Following the arrows to a cluster of leaves, in 671 we finally get a vague glimpse of the stem holding that giant "leaf" (or whatever it is) up. The three dimensional nature of the scene - objects in the sea rather than just flat ground - seems to be demonstrated as the appearance changes with differing points and angles of view.
Also some other selected images of aquatic plants are shown: Bottom left, some shots of the "bent arrow". Right side, stems rising up from the sea floor, one at the lower right in 337-mri and more centrally in 388-mri splits into 3 veins at the base of a huge leaf the surface. The whitish "island" towards the right in 337 is probably also a leaf mat - we see it floating above a deep area rather than being shallow 'water' forming a shoreline.

Oodles of seaweed! Titan's waterways seem as choked with giant plants as Earthly duck ponds or swamps are with small ones.

The sprays from the "Seas" chapter again. This time, let's look at the other features. Those seem to be plant leaves or a stem that the flow hits to make that spray. Left: Big leaves are seen in the background. Right: There are many stems in the water; some large light colored ones curving around and some smaller dark, "jagged" ones with leaves.
Having re-examined these as I colorized them, I suspect the main features aren't sprays of liquid at all. The edges as seen on the left (650) are so well defined it seems more like a leaf sticking out of the water. Titan doesn't seem to need study by astronomers so much as by biologists, and bio-chemists!

July 15 2006: Best yet! This image, PIA08115 (here reduced in size) from DISR, was posted almost the same day as my last one. It has generally better quality, the image artifacting has been eliminated, and problem areas have been well treated. The left edge has been cropped, removing the troublesome upper part, but unfortunately also some interesting bits lower down. The view of The Moon on the right gives a sense of the image scale: Things are closer and smaller than expected because Huygens' imagers are quite low to the ground compared to a standing person, and maybe Titan's closer horizon plays a part as well.

Fine MRI and HRI views are shown. There are some interesting features that are probably small plants about at the margin between the SLI and MRI view, though their exact forms remain elusive. Near the bottom of the MRI area is a very peculiar form that proves you can't go fishing anywhere without dredging up an old shoe! The HRI section is inevitably badly out of focus: one can't look clearly at one's feet through a telescope - here we needed instead more of a microscope, or perhaps a magnifying glass!

Some of what I was calling "mud on the glass" at the upper side of the far shore in my image, towards the left, could possibly be big seaweed leaves draped on top of other things, hence the appearance of features crossing over other features without completely obscurring them could be real.

IIRC, the spectroscopes resolved just a few pixels across the entire image view, much larger than the individual fine image features here, so to a great extent we have merely the average of the colors. It's probably better than monochrome, but not by much. One can't discern by color, for example, whether the larger roundish objects at the bottom of the SLI view are similar color to the things that are definitely attached to stems. A greatly different color might indicate they are unrelated, for example they might be clams rather than leaves. The left one especially seems clam shaped.

Grass in an inch of water. Note the reflections that show a few stems are above water, and the shadow of the leaf in the upper corner, and compare these with the shadows in the Huygens surface images above this one.
 

This image shows how difficult interpretation of image features on a living world can be in monochrome. Can you discern which areas are duckweed and which are white foam? Can you tell which blades of grass are vertical and which are horizontal?

(Color image "answer" below.)

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Color image "answer" to monochrome image.

Animal Life

There are promising signs of possible animal life, but nothing that seems reliable beyond serious doubt. There are a couple of things that look perhaps like starfish in the after landing view. One appears to be sitting on a large leaf and weighing it down. Something drifts or swims by while Huygens is on the ground, appearing in one of the MRI frames, but it is pretty small and formless and could be almost anything. And there are a couple of images during the descent that show what may be gigantic sea creatures, though these are highly suspect. One can see creatures in the forms of passing clouds just about as easily.

It only stands to reason that anything but Titanic (huge) animals would have been too distant for Huygens to make out during most of the descent, and alas there are no pictures between 1/2 kilometer elevation and the ground. At some earlier points I thought I could see a the head of a seal, a giant newt and a huge squid in the descent images, but upon further examination they don't seem very convincing. The "seal head" is probably some vegetable apparition similar to the floats put up by kelp only much, much larger. (Image SLI 698. Many large roundish "kelp float balls" are also visible in HRI images.)

The "newt" appears to be a geological formation of some sort (plus the usual sprinkling of seaweed) and anyway is too huge to believe.

The "squid" is more believeable in size but at 100+ meters still bigger than any Earth creature. At least some of its "tentacles" look like seaweed.

Unfortunately for seeing any land life, Huygens descended over the 'water' area, and the last views of land (besides small tide flats or mud or silt bars) are from almost three kilometers up:
 

Almost at the right end of the land, we see a big fat stem of a giant plant, rising from the sea and climbing onto the shore. Such stems creeping onto the shore appear here and there in the images, mostly distant views, and also in the closest Cassini images from space. The plants seem to spread like horizontal vines, stems with branches growing out of them. Or, my Earth viewpoint may be backwards, and these are plant roots on the land, supplying plants in the liquid. A third possibility is that the function of these growths is to collect and metabolize hydrocarbon haze particles drifting down from the upper atmosphere. Whatever, this whole landscape has neither rivers nor roads nor linear fissures, but giant plant growths creeping between the sea and the land! The near point of land looks especially 'bushy' or at least convoluted. The long skinny "islands" offshore also seem to be stems of plants. Other broader islands could be leaves or mats of leaves, or mud/silt bars. The area of strange sea plants shown in photos above is partly in view at the far left, including the "bent arrow". Behind the island are seen the linear features dubbed "cat scratches" when fields of them, lined up, were seen by Cassini radar, and which may be huge plant stems, aligned with the tidal flows. The closest one looks like it is connected to the large root or vine system towards the left side of the island.
(Panorama by René Pascal: http://www.beugungsbild.de/huygens/huygens.html)

A point of indirect evidence in favour of the existence of animal life is something that looks like a large leaf with two spots and some lines on it, seen just above the "shoreline" just right of center. It reminds me of tropical plants whose leaves or flowers mimic very specific flying insect parts, in order that that insect will land on it and try to "mate" with it, thereby (iirc) pollenizing the plant. I can't think of a reason the "leaf" (or is it a flower?) should be so decorated unless there are insects to trick.

My opinion at the moment, barring spotting something more definite, is that Titan probably has animal life just because it has plant life that looks quite far evolved, but anything one might consider to be direct evidence is highly suspect. Is it possible for a world to have evolved all that interesting plant life and yet have no amimal life so far?
 
 

Cassini Views

Having glimpsed the nature of the landscape with Huygens, we can now turn to some more distant views from Cassini and make sense of them, which we wouldn't have been able to do without Huygens. That individual plants appear to be visible from space as far as Cassini must stay from Titan is remarkable to say the least. Color photography from Cassini's VIMS camera shows the colors of the objects within or covering much of the liquid are different from the land surface color.
 
 

ColorCassini VIMSview showing Titan's colorful seascape in "false" infrared colors. (Makes my colorizations look conservative!) It appears to reinforce the Huygens plant views.
Best guesses: The whitish areas are land areas, above liquid. The dotty blue areas on the land are roots or vines. Compare the 'vines' and gaps between islands with the Huygens panorama above. The one at the top may be holding the ground in place with its roots and preventing the tide from washing it away. Irregular dotty linear features in the sea would seem to be aquatic leaves and stems. The scale is mind boggleing.

 

Clippings of Cassini Titan images from space (Top & Left or Middle). The second image was evidently taken from just 1200 Km above Titan's surface which possibly makes the rez 7 meters/pixel - most are from much greater distances. At the finest visible levels, the features vaguely correspond, but exact matches are not seen. This is true in any digital images, but more so here. We are probably seeing finer detail than it might seem when comparing the two images. Factors causing differences from image to image of the same area include (a) atmospheric distortion, "twinkling", which may shift the position of a feature as well as make it more or less visible, (b) the time of day of the image, because the shadows of the vines, especially on land, will move and change in form and intensity, (c) the tidal flow because it may cause aquatic plants to shift in position and orientation, and (d) the actual sea level with changing tide, though I'm still looking for a definitive view of this. For comparison, the image of Enceladus terrain from 5200 Km at 30 meters/pixel (right or below) shows the quality of the optics.
On the northwest island especially (2nd image) as well as elsewhere, the outlines of huge "vine" plants or root systems of sea plants seem to be visible coming out of the sea and spreading across the land, similarly to those on the island Huygens viewed. The dotty patches in the sea also seem to be plant parts - even individual branches of leaves seem visible here and there, though accumulations of duckweed on Earth ponds can have a similar appearance and they are actually composed of many small independent leaves (see duckweed image above). The shorelines seem indistinct probably partly because of the gradually shallowing liquid and beaches, and partly because in that shallower liquid, more plant leaves cover the surface. All those plant leaves on the sea surface probably confuse radar findings, searches for glints of light off open liquid, and spectral readings expecting liquid methane. Note also the streaks of the tidal flows, silt probably creating shallows in the tidal lee of the islands. Titan's tropics may be vast swampy wetlands.
The top image only vaguely corresponds with the view from Huygens, whose landing area is, unfortunately, just to the left of the second image. (More recent imaging has located the actual landing spot within Cassini space views.)
 

This image  of the South- and North- Saturn Seas was taken by Cassini's Visual and Infra-red Mapping Spectrometer. It appears to show colored aquatic plant growth obscurring much of their surface.
(The equator runs between the two seas, South is left, and about the image bottom faces Saturn.)

Discussion of Titan Life

(There may be a bit of repetition between the top section and this one, sorry. Needs editing!)

Biochemistry

 
Methane eventually decomposes in sunlight, and its continuing existence on Titan indicates that it is being replenished. If it is being breathed by animals, even more does it need continuous replenishment. In spite of 12C/13C carbon isotopic readings that might point elsewhere on Earth, a biological source of replenishment seems very likely, and that's where plants come in. It appears that the bulk of Titan's methane was originally locked up underground in combination with water ice, and that geological heating over time in three great epochs cryovolcanically released the liquid and atmospheric methane Titan has today. But it is also reasonable to assume that plant life on Titan replenishes the methane, as Earth plants daily renew Earth's oxygen supply.

Much new information from the Huygens landing was made public in December 2005, including statements about the spectrographic findings. Spectra of the surface were much different than those of the atmosphere, indicating complex organic processes are indeed occurring, unique to the surface. These are the very sort of things one would expect to find if there were abundant life on Titan, just such life as seems to be shown in the Huygens images, but are difficult to explain away on an inert surface. Here are some of the statements:
 

The whole article is here: http://www.esa.int/SPECIALS/Results_from_Mars_Express_and_Huygens/SEMK1TULWFE_0.html

More was published in the journal Nature that same month:

"The reflectivity of the surface at the landing site was measured from 480 nm to 1,600 nm without the interference of methane absorption bands or haze opacity. The peak reflectivity in the dark regions is about 0.18 at 830nm and decreases towards longer and shorter wavelengths. The red slope in the visible is consistent with organic material, such as tholins, but the blue infrared slope is still unexplained. Between 1,500 and 1,600nm the reflectivity is low (0.06) and flat, consistent with water ice. Nevertheless, the decrease in reflectivity from 900 to 1,500nm does not show the expected weak absorption bands of water ice near 1,000 and 1,200 nm, and the identity of the surface component responsible for this blue slope remains unknown." -- Nature04126.pdf

The several Nature articles were found here:
http://www.nature.com/nature/focus/huygens/index.html

My appraisal is that the entire area, if not the entire tropical surface of Titan, is a sort of giant wetlands. Huygens appears to have landed on something like a "silt bar" partly covered with vegetation, probably composed of organic sludge raised by the tides in the sea to just about surface level. I would suggest there was nowhere for the spectrometers to look and Not see organic matter and life, and having viewed the images these findings don't seem surprising. Whence cometh this complex organic chemistry with unexplained spectra if not from life? Can it all be explained by a dead, dry surface with rocks on it?

On a clear day with the sun overhead, sunlight is delivering 100 watts per square foot to the Earth's surface. Saturn and it satellites receive only one watt. Titan under its rather obscurring atmosphere receives considerably less solar energy, currently estimated at around 1/10th watt per square foot. This is still 350 times brighter than Earth under our full moon. In our north on an overcast winter's day there is also only 1 watt. Even on Earth, there are deeper sea plants and perhaps shade-loving plants that thrive with as little light as Titan gets or less. So energy-wise, plants are possible but likely to be slower-growing. On the other hand, the limiting factor to plant growth on Earth is not sunlight but the availability of that vital trace gas, carbon dioxide (CO2). If extra CO2 is introduced in a greenhouse, plants grow faster.

There is probably a trace gas or multiple trace gasses plants need for photosynthesis on Titan, too, so if that is somewhat more abundant than our CO2, it does not necessarily follow that Titanian plant growth is hundreds of times slower than Earth's. Indeed, one may suspect from their size that they must grow rapidly indeed, or else live a very long time. Plants could also filter out various trace organic aerial compounds for their carbon, and combine the carbon with the hydrogen to produce... you guessed it, CH4, methane. One report suggests that Titanian plants could gain indirect solar energy by converting the energetic particles formed by ultraviolet induced methane breakdown in the upper atmosphere (where the sunlight is full strength), and thence drifting down to the surface, back into methane, and that this cycle could actually provide more energy than direct photosynthesis itself.

Two factors limit the size of trees on Earth: gravity and wind. Titan has only 1/8 of our gravity but the air is thicker, so how tall plants and tress can grow on Titan is likely to be limited by their resistance to being uprooted or broken by the wind, which in turn is related to the highest normal wind speeds. Huygens measured 15 Km/hour surface winds, but we have little idea whether more severe weather is to be expected frequently, rarely or never. But Titan does not currently seem to have trees as such. Instead, various types of gigantic vines, or the root systems of various aquatic plants, grow out of the sea and spread over the land. They all seem to originate or end in the sea. Perhaps the land is currently too dry to support plant life. Earth was very dry in the Permian period and the early Triassic period on Earth.

Other aquatic plants prefer to stay in the methane, growing leaves up their long stems or growing up to the surface and forming giant "water lilly" mats. Whatever else they are, some Titan plants are Titanic! (What a well-named planet!) It is possible Cassini has been seeing beds of them from space, and it seems small wonder that the shallow, very transparent seas with mats of leaves on the surface don't provide very distinct shorelines to Cassini's imagers.

I should mention some forms of Titanian plant life I've noted but haven't touched on elsewhere.

One is "Titanian Kelp". On Earth, beds of kelp grow in shallower ocean areas with strong waves. These annuals consist of anchor roots, a very long stem, a float bulb, and limp leaves. The float bulb drags the leaves up to the surface where there is the most light. Titanian kelp is probably similar, but the float bulbs and their waving leaves seen in the descent images are gigantic, instead of bulbs just a few inches across. Features in SLI 698 (below left) may be a bulb and some leaves. The possible "bulb" looks like it has eyes, and double eyelike features are seen in a number of other places as well.

Another is, for want of a better word, "horsetails". There are what appear to possibly be striped stems at various sizes from huge in the descent images to small at the bottom center of the SLI after landing images. This and other vaguer ones on the ground are too close to the camera and out of focus, and may be ordinary dark stems with leaves at intervals (they may be "horse tales" instead!), but the ones in the descent images certainly have much the appearance of horsetails.

Finally, features dubbed "cat scratches" in Cassini RADAR images seem to be giant horizontal floating stems, aligned with the tidal flows. Two match up between the RADAR and distant Huygens views. One in the Huygens views appears to connect with the huge root or stem crossing the land area and once dubbed the "landing strip". What may be a smaller specimen of one of these is seen floating on the sea in image SLI 710. (Note the "horsetail" stripes on the stem.)

We can probably expect primitive animal life such as shellfish, sea worms and so on to be as abundant on Titan as on Earth. Many species might be similar to Earth's, or there might be species dissimilar to any we've encountered here. Evolutionary potential seems to be essentially "pre-programmed" into the genes of the first life according to some recent studies, and the species that evolve depend on the ever-changing environmental conditions, and to some extent, "luck". Obviously, if there were no oceans, there would be no sea life, and if the air was too thin, there would be no birds. Earth's flying reptiles could perhaps have outlived the dinosaurs if they had evolved a bit differently, and if they had, we might have a few small species of them in warmer climates today. If we saw flying reptiles or quite unfamiliar creatures on Titan amongst other more familiar forms of life, we shouldn't be too surprised.

The potential size of animals to be expected is interesting. Intuitively, if the world is smaller, the life will be smaller, but this does not follow. In fact, with only 1/7 gravity pulling it down, much larger animals might be expected. For example, on Earth a person twelve feet tall would have to be built somewhat like an elephant to support his own weight. On Titan, a twelve foot tall person could be quite lightly built, and might have longer legs in proportion to his body than an Earth person. We might also anticipate many species of birds and other flying creatures with small wings, as the light gravity and thicker air should make flying rather effortless. The motions of the animal life would probably be slow and graceful by Earth standards, as the muscle mass we need to exist and move around just isn't required on Titan. It would probably be more important for animals in their quest for survival to use less energy and hence need less food. (Earth's sloths do something of this nature, but they doubtless shouldn't be considered a close parallel.) The entire pace of life would seem to be slower on Titan, with the lazy gravity, the low temperature, and the extraordinarily long day and year.

However, the only possible signs of Titanian animal life are sketchy at best.

July 2006: I've just looked at PIA08112 and other recently released COLOR images from the Huygens probe. PIA08112 is a bear to download and try to view, but it is six of the best views ever done of Titan looking downwards as Huygens descended. It appears the spectrographic data was incorporated into the imager data to provide actual if low-rez color, but the caption is unenlightening. I can't say with any sort of assurance, but there are some patches, especially at the right end of the "oval", that are most reminiscent of "bio-diverse" beds of mussels and clams with seaweed and snails, attached to rock outcroppings. (but if so, they are gigantic!) Mussels and clams are of course animals, with freeswimming larvae, so this (along with the idea that some of the roundish objects in the after landing view may be clams) is another bit of - very tentative - evidence of animal life on Titan. Or it could all be seaweed or even boulders, giant gravel bars. This excerpt is from 8112's third view (middle left):

Excerpt from PIA08112-c. Huygens' landing site is towards the lower left. Near the shores, one seems to get some idea of the depth of the liquid, and there is the sense that liquid is flowing, pouring over the rock, from left to right, Eastwards. This is in fact the correct direction for the tidal flow at the time of the landing.

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Copyright 2005 Craig Carmichael  all rights reserved