"Life resists arbitrary boundaries, distributing itself
according to the conditions of the environment rather
than to man's measure of geography."
-Jacques Cousteau, "The Ocean World" 1979
Since man came to the realization that he was on but one of several terrestrial planets in our solar system, he wondered if there was life on the others. We looked for neighbors in our own solar system; from the fact that Venus looked similar to Earth, we believed she could be a tropical sister. From the trenches and strange faces on Mars, we believed a vast civilization could be dwelling just out of reach. Even the term "Martian" which has become synonymous with "space invader" means one who has come from Mars.
With our space probes, we discovered that Venus was a hostile world where no life could possibly exist. The planet was in constant turmoil beneath clouds which rained sulfuric acid below. We found that whereas Mars might have held life long ago, we were too late to have seen it and that there were clearly no Martian cities awaiting us. We became disillusioned to the thought of life in our own universe. We once again receded to the medieval view that life on Earth is special and must appear nowhere else in the universe.
But what is our premise for this? The study of two terran planets in our nearest backyard. There is not only an entire galaxy, but an entire universe left to consider. We have yet to even look beyond our asteroid belt - and we are ruling out life beyond our own.
In the following pages I will attempt to prove that life as we know it could easily exist in our universe outside of Earth. I wish to prove not only is it clearly possible- it is possible in our own solar system. For this I have chosen to examine two moons of Jupiter: Io, a volcanic moon pock-marked with craters and surface activity; and Europa, a frozen ice ball locked in orbit around the gas giant. These two moons are large enough that if they orbited the sun instead of Jupiter, they would count as planets. What, then, might they hold?
First, to examine Io. Io is covered in volcanoes and mountains and is a constant source of tectonic activity. This is due to the slightly elliptical orbit it holds around Jupiter. The gravitational pull on the moon from both Europa and Jupiter causes it to flex and stretch, friction heating it up. This is called tidal heating. It is important to take this into account because as far out from the sun as Jupiter is, heat is a commodity. Not enough warmth from the Sun reaches the moons and so an alternate source of warmth must be located for any life that may be present. Io, which produces more than 200 times the heat of Earth's geological movements, by comparison seems to have no problem keeping warm.
Io is the size of our own moon, with a synchronous orbit to Jupiter. The volcanic activity on Io is constant, shaping new mountains on the surface. These pock-marked volcanic peaks are actually quite similar to those on Earth and Mars. Io appears as a planet which is attempting to look like our own Earth, a fiery surface swept in metamorphosis like the Earth was before life had a chance to evolve. Because of this I believe there is no life on Io at current- it is simply too violent and ever-changing to allow life to develop in any way we are familiar with. However, because it looks so much like primal Earth, what of the possibility of life in the future?
All this heat and volcanic activity means that many gasses are being expelled into the atmosphere, but are they staying with the moon or being swept away by Jupiter's pull? When the Galileo spacecraft visited Io, it flew through a high altitude ionosphere. What it found was that 555 miles up, the ionosphere consisted of ionized oxygen, sulfur and sulfur dioxide. The ionosphere was not stripped by Jupiter as they thought it would be- it, in fact, stayed with Io. Earlier spacecraft Pioneer did not see this and so it was unknown before Galileo. Many other things had changed between Pioneer and Galileo's visits, not just the ionosphere. The surface too was extremely different. Io is a world in progress. The implications of the changes in the ionosphere that Galileo saw are that it and the atmosphere -that which will be needed for life- will probably change over time with periods of more or less volcanic activity.
Still, much about Io is different from Earth. Io's tectonic motions are influenced more strongly by its elliptical orbit than Earth's had been by the pull of the Sun and Moon. While Earth's tectonics move on a lateral plane, Io moves on a vertical. Magma moves upwards to the surface where it spreads outward over the old lava. The old surface is buried and compressed down further and further until it breaks apart, leaving new pathways for magma to reach the surface. However, on a planet of such constant change there are some permanent fixtures. There are mountain ranges that are as high as nine kilometers. This means that to a degree, Io is attempting to stabilize itself. However, because of its orbit with Jupiter, this process is taking a far longer time than it originally would. In fact, Io will probably never stop with its constant activity. The same forces which induced the tectonics are those which ensure they will never stop.
So is life possible on Io? Io has the potential to suit life as we know it, but in a far and distant future, and only if something drastic breaks its elliptical orbit. In the lifetime of Humans, life will probably never be found or capable of surviving on the volcanic and ever changing moon Io.
What of Europa, then? At first glance it seems little more than a frozen ball of ice in an elliptical orbit around Jupiter. Its tidal heating is less than Io's, but still most likely the main source of heat for the moon at its current distance from the sun. While she is covered in ice, it may not be water ice. Is this small frozen moon somewhere life could potentially develop?
First, the surface and the crust of Europa is indeed made up of water ice. Water is the essential piece of life on Earth, and human beings ourselves are made up of mostly water. Life originated in the seas and would probably remain strictly there today too were it not for the presence of land. Tidal heating could, in fact, melt much of Europa's ice into liquid form below the surface. If this were the case, Europa would have an ocean over 100 kilometers deep. That is twice the depth of all of Earth's oceans combined.
Some researchers believe that below the surface there may simply be warm convecting ice rather than water. However, what Galileo found indicates otherwise. The spacecraft observed that Europa had a magnetic field. Moons seldom have magnetic fields of their own. Galileo also noted that the magnetic field of Europa changed in tandem with Jupiter's field. What this means is that Europa would have to be made of an excellent conductant- a conductant like water. Ice or slush would not yield this result. Better still, because of the extent of the conductant needed, it is suspected that Europa is not only water but salt water. This water can not simply exist in pockets between the ice, either. In order to conduct to such an extent, water must be present throughout the entire moon. The uniform salinity and the level at which the magnetic field is conducted indicates that Europa's ocean is about as saline as our own. To confirm this, Galileo found salty compounds on the surface of Europa.
Thus we come to the second problem concerning life on Europa. Indeed, the salt water could support life. However, there is far too little sunlight available to the water moon to justify what we commonly think of as oceanic life. Until recent years, this would have stopped any theories of life on Europa dead in their tracks. However, with the discovery of hydrothermal vents on Earth comes a plethora of new knowledge about aquatic life.
A hydrothermal vent is like a small underwater volcano, far deeper in the ocean than light from the sun will ever reach. It was believed prior to the discovery of hydrothermal vents that once light and heat had ceased to be present in measurable amounts, life ceased existing in the ocean. There was an imaginary line drawn. However, Jacques Cousteau, inventor of the SCUBA gear and renowned oceanographer turned the marine biological world on its head when in the 90s he discovered the hydrothermal vent. Not only was there life in the deep, cold ocean- there was life that had previously never been heard of before. The tube worm, an animal that lived without ever seeing sunlight and subsisted in colonies around the hydrothermal vents. New varieties of crustaceans were found, new fish as well. These animals lived so deep in the ocean that they had to be brought to the surface in pressurized containers, otherwise they would explode as the pressure dropped. Even so, none of the specimens Cousteau brought up were able to survive. These animals had lived far deeper than any Human had ever even dreamt of life existing. Their entire ecosystem was worked around the heat and minerals put out by these underwater volcanoes.
Because Europa has the same kind of elliptical orbit which causes Io to be a never-ending wasteland of volcanic activity, it is fairly safe to guess that far beneath Europa's icy surface and salt oceans there are hydrothermal vents. Due to its composition, water holds in heat and loses it slowly. The areas around hydrothermal vents could easily remain warm enough for creatures similar to tube worms to develop. The gasses expelled through these vents are dissolved in salt water- salt water on Earth holds all the pieces necessary for life. Carbon dioxide, one of the gasses needed for plant life, is in much greater concentrations in water than in the air. While we have been taught in classrooms all our lives that plants require sunlight to survive, Jacques Costeau himself writes in his 1979 book The Ocean World that plants are capable of oxidizing in darkness.
All the pieces are in place on Europa for life as we know it at the current time. Chances are there will be no dolphins or other mammals in Europa's oceans- warm blooded animals require much more oxygen than cold blooded creatures and without a surface area, they probably could not obtain it. However, if a program to examine Europa's oceans arrived there this very moment and searched the oceans, it is quite possible they could find nothing. This is not because life is nonexistent. Some ocean animals are so small that they could fit between grains of sand. Not only is size a factor in their discovery, but the water itself poses an obstacle. Even in the clearest of sea water, with bright sunlight, trained divers can only see about 100 feet around themselves in any direction. At a depth of a mere 2000 feet on Earth there is no Human perceivable light. In the far off depths of Europa's dark waters, how can Human perception even hope to find life? We would be blundering hopelessly. Unless something found us first (which is unlikely, as the dwellers of hydrothermal vents hardly leave their own area), we would likely find nothing due to current biological and technological limitations. We can not even reach the bottom of the Marianess Trench, let alone the bottom of a 100 kilometer deep ocean.
Is there life on Io? No, but the potential is there for a far and distant future. Is there life on Europa? There is no reason to believe otherwise due to evidence present in our own Earth oceans. The quest, then, is not whether or not there is life in our own solar system beyond our own- it is how can we go about finding it?
In trying to answer this timeless musing, we only find ourselves present with another and larger question. If there is potential for life twice over in our own little solar system, what about the next one over? What about neighboring galaxies, how much life can be found in them? In the universe all told, how many creatures are dwelling, breeding and evolving in ways that we already can understand - just doing so out of our sight?