Inhabited Ganymede

Ganymede was discovered by Galileo Galilei and also by Simon Marius in 1610 along with Jupiter's other three moons, the first worlds found orbiting another world instead of directly about the sun. As is the case with many major discoveries, the established universities, and the church, wouldn't believe it was so. It was pointed out that "although the telescope acted well enough for terrestrial objects, it was altogether false and illusory when applied to the heavens." Galileo heard the professor of philosophy at Pia "labouring before the grand duke with logical arguments, as if with magical incantations, to charm the new planets out of the sky." But afaik, no one born since has tried to discredit the existence of the Jovian worlds, which are quite visible with binoculars and would be visible to the naked eye if they weren't drowned out in Jupiter's glare. (Anyone wishing to see the orbits for themself can note the positions of the four satellites next to Jupiter, then look again the next night, and see that their positions have changed.)

Seeing a world as a distant point of light and seeing what's on it, however, are two different things. Aside from their existence and, in time, "whole globe" statistics (orbit, mass...), little was known about Ganymede and Jupiter's other worlds for almost 400 years, until Voyagers 1 & 2 flew by in the 1970's and discovered they weren't just the balls of jumbled ice and rock they had been presumed to be. The Galileo Spacecraft finally photographed and otherwise examined it in somewhat more detail in the late 1990's. The Galileo discovered that Ganymede had not only ozone, but also its own magnetic field, both valuable assets for a life sustaining environment. And since Ganymede orbits inside Jupiter's Van Allen belts, Jupiter's magnetic field may also provide some protection. Although the ozone layer surely must hover right on the ground instead of being held aloft by an atmosphere, it is there to do its job of protecting living things against an excess of short-wave UV and higher energy solar radiation.

Another way Ganymede is lucky is that Io's volcanos give off particles of sulfur and sodium that are IOnized (another well-named world!) by Jupiter's magnetic field, and the Io plasma torus around Io's orbit is so radioactive that an unprotected human would almost immediately be exposed to a lethal dose of radiation. (That's what did in Galileo's camera.) Even the next moon out, Europa, is within the danger zone. It is unlikely that however far our technology advances humans will ever visit Europa, much less Io. Planet Ganymede (larger than Mercury and 1/2 the size of Mars) is evidently out of this killing zone and in a quiet space region.

There are important things Ganymede isn't protected against, however. One is bombardment by micro-meteors. Over a million of these high-speed bullets, most no larger than a grain of sand, stream into the Earth every day and are burned up in our protective atmosphere. On an airless world, they must surely constitute the greatest of all hazards to life and health. Our spacecraft and space suits are designed to hopefully withstand a stray hit or two, but "space walk" time is rightly considered hazardous. Another, perhaps the other, environmental hazard on an airless world is space weather, those occasional electro-magnetic, energetic coronal mass ejections of the sun that so threaten Earth's communications satellites orbiting above atmospheric protection.

We in our Earth-centric views have considered that an atmosphere and liquid are essential to life. In the past, many went further and were sure liquid water, H2O, is the only liquid for life and that the temperature must be Earthlike, but that myth has been dispelled in the botanical splendour of Titan's methane seas at 94ºK, just 1/3 of Earth's thermal energy level (285ºK) (In degrees Kelvin, water freezes at 273º and boils at 373º, and molecular motion ceases at 0º - absolute zero.)

We atmospheric beings had no reason to believe that life on an airless, and hence liquidless, world was possible until we noticed it in view on Ganymede. This in spite of the Apollo 12 crew having brought back a still alive microbe from from Earth's moon, riding on a piece of a previous unmanned moon landing craft, Surveyor 3. So little did we suspect the possibility of airless life that in the several years since the images were taken no one has taken much notice (but see the "Prior Rumours" section). If I am able to dredge up any theories about the chemistry of life in what is essentially a vacuum, I'll reserve the discussion for the Ganymedian Life Speculation chapter. When I was young (1960's) I heard that earlier reports of UFO's often coincided with certain Earth-Jupiter alignments. Since I was sure there could be no life of Jupiter, that sounded silly - such was our presumption that the moons were just small chunks of jumbled ice and rock that life on one of them wasn't even "on the radar screen". I once read an interesting science fiction story about an astronaut finding life on a moon with no air, but I can't recall the author, or the moon in question if he named it. (The difference in lighting between sun and shade on airless worlds was very much overstated, a popular misconception in the early 1960's being that in the shadows everything would be pitch black.)

Ganymede's temperatures are naturally in between Titan's and Earth's as it is between them in distance from the sun. Ganymede gets only 1/25th of Earth's solar energy (4 watts/sq.foot versus 100 watts/sq.foot), but there is no atmosphere to attenuate it as happens on overcast Earth days. It get four times as much as the 1 watt per square foot that strikes Titan's atmosphere - of which only 1/10th reaches Titan's surface as sunlight through the methane vapour. On an overcast day in northern latitudes, Earth's insolation can also be as low as 1 watt per square foot. In the shade, insolation is also attenuated to Ganymede-like figures, and plants do grow in the shade. Some deep-sea plants evidently grow with even less sunlight than Titan gets.

However, there is a great difference between temperatures on an atmospheric world and a non-atmospheric one. Heat radiates more slowly through a vacuum because there is no direct contact with material of a different temperature, but there is no blanket of air to hold heat in at night. Earth would be too cold for life at night without the atmosphere, and Titan with its somewhat denser air stays pretty much the same temperature 384 hours a day. While Ganymede may attain to 140ºK and probably considerably more in selected locales in the daytime sun, it drops to about 90º - 95º during its 86 hour night, as cold as or colder than Titan, which is twice as far from the sun. (Airless moons of Saturn, for comparison, are 70ºK (icy) to 80ºK (darker surfaced): Titan's methane seas, like Earth's water oceans, would freeze without the atmosphere.)

Viewed as a globe, Ganymede appears to have two types of terrain, darker and lighter. The darker terrain evidently has more meteor cratering and so must be geologically older, while the lighter terrain was probably liquid welling up from the interior at a later date, perhaps as extensive icy lava flows. This lighter terrain is ice-rich, or mineral poor depending on your point of view. An unusual feature of the ground that sets Ganymede apart is the grooves. Huge grooves, small grooves, rows of newer grooves splitting and criss-crossing older grooves. Grooves like long sand dunes or waves on the sea, but all (it is believed) frozen into place 100s of millions of years ago as Ganymede became geologically more inert. Only later meteor and comet deposits would have brought other, including heavier, minerals to these areas, whereas the darker terrain that didn't get overturned and mixed into the interior beyond an early date has less ice and more heavy minerals. But some of the grooves appear to be natural rows of vegetation.

Since nobody imagined there could be life on the surface of an airless world - and I have no plausible theories about the chemistry myself - few evidently paid close attention to the images that were returned; everyone concentrated instead on the exciting volcanos of Io and the strange seas of Europa! There has been no Ganymede lander or orbiter, and current plans are vague. The Galileo, on its trips by each of Jupiter's moons, was moving very fast relative to them, and many images (evidently) were lost from the closest pass-by of Ganymede on orbit 29 owing to camera malfunction. (Io's radiation even killed the radiation-resistant camera!) Nevertheless, since Ganymede has no atmosphere, it was possible to whiz by quite closely, unlike Titan where atmospheric turbulance could cause loss of control if Cassini came within about 700-1000 Km. Although there are only nine images with a resolution of less than about 60 meters per pixel and the three closest are badly saturated, there are a number of very interesting Galileo images of Ganymede from a close enough distance to show that while craters, rocks and ice are present, they are not the most interesting features of Ganymede's surface.

Ganymede's gravity is only about 1/7 of the Earth's, about the same as Titan's. This is even less than our moon's gravity (1/6) even though Ganymede is 3-1/2 times the size of our moon, because Ganymede's core contains many lighter materials such as ice, and so it is less dense. Ganymede's 7 Earth-days day is long to us, but not so long as Titan's 16 days day.

I read in The Urantia Book many years ago (1982) that there is an essentially airless world "in close proximity" to ours that a race of "non-breather" people call home. But if it was true, where could such a world possibly be? A survey of the solar system at the time didn't seem very promising, yet what else could "close proximity" mean but a world in our solar system? Our moon and Mercury looked pretty dead, Venus had air. Surely nothing beyond Saturn could be warm enough for life. Titan had air, so unless it was some absurdly tiny moon like Iapetus or Rhea, that just left three of the four moons of Jupiter, which we knew little about except from some awesome but rather distant Voyager images. As our space explorations continued, it eventually became pretty easy to narrow it down to Ganymede or Callisto, Io and Europa being in space zones too radioactive, among other things, for serious consideration.

Then I read that organic "tholins" had been detected on Callisto. Callisto had a strange surface variously described as "fluffy", "gritty", "mobile" and "dark". Craters seemed to have oozed flat by some process that seemed more like "mudflows" than "landslides", and any small surface features were obliterated or hidden. Surely here we had an airless world where things out of the ordinary were transpiring! But this was all circumstantial evidence, and on Galileo's 30th orbit, some very hi-rez pictures were taken, which simply showed more inscrutable black surface and some steep ice hills. I had conjectured some odd things in certain more distant images might be very large trees, but these close-ups showed that such features would actually have been more of the steep hills.

Strange to tell, I didn't take any more serious look at Ganymede than anybody else. I glossed over a few images, and I thought they looked "fuzzy". Too much contrast: must be glare ice! All this was in the period from 1996 or so, when Galileo began to return wondrous pictures of Jupiter and its moons, to 2001, but mostly 2000 and 2001. After 2001, all sat in limbo until January 14th 2005, when the Huygens lander descended on Titan. I didn't immediately see any life on Titan and I didn't expect to see any. But I did see liquid methane, which, contrary to the visual and instrumental evidence, people had decided wasn't real. I started studying the images to prove that it was. But there was this odd thing that looked like a seal's head in one image, and it had some strange companions. So I decided to look for things that looked like life. There was a giant newt, clear as day, in four images. And some other things. On the land, there was something I thought at first looked like cleared land with roads and houses. Shouldn't such things be visible on "the non-breather" world? It was at that point I decided that, having seen nothing definitive on Callisto, I would go back and look at the Ganymede images.

Sure enough! There they were - bizarre creatures on tentacles, "craters" or "rings" with "tongues" licking out of them. Poles in rows. What looked like a giant house. Landscapes that looked something like coral reefs. Holes burrowed into the ground, and underground "tunnels" exposed on the side of a cliff. Strange things like sheets of polyethylene - or electric fields - strung up for miles. And most bizarre of all, a giant "face of E.T.", much more believable and detailed than the so-called "face on Mars", but definitely not an Earthman's face.

I didn't know what was going on on Ganymede, but it sure needed another look! Poles don't erect themselves in rows or circles by themselves! I decided I'd finish my studies of Titan (which is actually in a primitive evolutionary era) and then revisit Ganymede, and this visit is what this web site is about.

Even more than with Titan, I make no claim that every brush stroke is correct, but I firmly believe I'm showing the astounding Real Ganymede... as far as I've been able to make sense of it, which isn't very far.

Size	5276 Km Diameter; 30% larger than Mercury; about the same size as Titan; almost half the size of Mars; 1/14 the size of Earth (by volume). The total surface area is 17% of Earth's, or 3/5 of our Land area, or 87 million square Km.
Density	1.94 - about twice that of water. (Earth, the densest planet, is about 5.5.) Surface gravity is 1/7 that of Earth.
Atmosphere	No appreciable atmosphere. The exosphere contains oxygen and ozone. The ozone is generated by sunlight striking ice; Ganymede also has a magnetic field. These factors protect life from some of the violent solar energies our star emits. ...But not from micrometeors!
Seas	Open liquid is not possible without an atmosphere: all materials go directly from solid to gaseous state at their melting point where there is no air pressure.
Surface Temperatures	up to about 140-160 degrees Kelvin during the day, 90-95 K at night. This is less than 1/2 the thermal energy of Earth. (Earth is around 280-290 K.)
Distance from Jupiter	1.07 Gm (Giga-meters); Earth's moon is 400 Mm (Mega-meters) from Earth
Length of day	7 days, 4 hours (Earth days); Ganymede orbits gas-giant Jupiter once in that time, and keeps the same face always towards Jupiter. (Europa, the next world in, orbits Jupiter in exactly half that time, and Io, the closest, in exactly half the time of Europa. These orbits are termed "tidally synchronous" and they cause internal heating of the three bodies, especially Io and to a lesser extent Europa. Ganymede is affected least.
Distance from Sun	780 Gm (Giga-meters); Earth is 150 Gm
Year	Almost 12 Earth Years; Ganymede is 5.2 times as far from the sun as Earth. The small orbital inclination and axial tilt essentially means Ganymede has no seasons as we know them on Earth.
Inclination of Equator to the Sun (Seasons)	.2 degrees; Earth is 23-1/2 degrees. This effectively means that if Ganymede has any seasons at all, they are caused by any eccentricity of Jupiter's orbit around the Sun. (On Earth, the northern summer occurs when Earth is farthest from the Sun [94 million miles, versus 92 million in December], showing that equatorial tilt is the main climatic factor.)

Welcome to the Living Ganymedeweb site