Astronomy: The Jovian Moon Europa

Subject: Sciences
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Study level: Undergraduate


Ten years from now the National Aeronautics Space Administration of the United States of America popularly known as NASA is planning to send an orbiter to the Jovian Moon Europa (Silber, p.1). NASA is coordinating an international fleet of probes to once again invade the environs of Jupiter and study it even more closely (Silber, p.1) One of the major purposes for the said mission is to know more about Europa. There is only one simple reason why many are interested in landing a probe unto the said Jovian moon – there is evidence of a watery ocean in there. Water means life and if there is an ocean of it in Europa; therefore there is a tremendous possibility of extraterrestrial life. But a closer examination of current data will reveal that scientists hoping to find life outside the planet Earth may have set their hopes too high on Europa.

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Jovian Moon

Every time there is an article or a news flash written about Europa one almost always reads the label Jovian moon. This is because Europa is a satellite or a moon of a distinct type of planet. In the world of astronomy, there are two types of planets: jovian or Jupiter-like and terrestrial planets, those that are like planet Earth and Mars with a solid mass (Ulmschneider, p. 24). Jupiter-like planets are massive alright but they are made up of gas. This will provide some background information on what type of environment Europa is in. Even an amateur astronomer will come to realize that Europa is much farther from the sun than Mars, this will be a crucial piece of information when it comes to determining if life is possible on Europa.

Before going any further it is interesting to note that Europa was not a recent discovery or even an accidental discovery made by a NASA probe. This moon and even Jupiter was discovered by Galileo Galilei on January 7, 1610, when he trained his self-designed and self-manufactured telescopes into the night sky and he did not only noticed the distinct shape of Jupiter but also four brilliant pinpoints of light around the planet (NASA CIT, p.9). Galileo also noticed that these bright lights changed positions in a few hours and made the conclusion that these are four moons of Jupiter.

Galileo was considered the discoverer of the four moons but there was another rival observer in Germany named Simon Marius who also claimed credit, and it turns out that Marius indeed discovered the same four moons just a day late after Galileo did and so it was just fitting that today astronomers are using the names that he used to label the four moons based on classical mythology: Io, daughter of the River Inachus, Callisto of Lycaon, Europa of Agenor and Ganymede the handsome son of King Tros (NASA CIT, p.9). This is a brief explanation as to why the world has come to know this moon as Europa. More importantly, this is the reason why one of the spacecraft sent to observe this particular region on the solar system was called Galileo.

Vital Water

As mentioned earlier there is only one reason why space probes are aimed towards Europa – scientists believed that there is an ocean of water present in the said moon. This simply means that if there are vast amounts of water in Europa then there is indeed a possibility that life can occur there or that there was once extraterrestrial life on Europa – something that scientists still consider as amazing and therefore needed to verify and study.

Water is essential to life, without it there is no way that organisms big and small can survive. Water is needed by plants, animals, insects and even microorganisms. It is needed as a means to dissolve minerals and transport food and wastes to and outside of the body. Urine will never be possible without water. The digestion of solid food is impossible without water. The existence of blood and everything that it contains is impossible without water. In fact, the body is composed of more or less 70% water underscoring its great importance to life.

In order to highlight even further the importance of water one can examine a neighboring planet known as Venus. This planet is near the sun and within the region called the habitable zone. It is the right planet size as compared to Earth and it is not a gaseous planet like Jupiter and yet it could not support life because there is no water.

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However, it is not merely enough to have water on Earth, in order to sustain life this planet must contain liquid water. This is because many organisms live in it and “…all organisms maintain an inner aqueous environment within which life’s chemical reactions occur and by which life’s materials, such as food, gas, and waste are transported” (Hays, p.1). It is not enough to simply have water, there should be liquid water.

Temperate Zone

This is the reason why there is an idea of habitable zones that was identified by astronomers. This zone is in relation to the distance of the planets to the sun and at the same time the effect it has on water. As many are aware water can appear in three different phases. It can appear as liquid, vapor, and solid. Water is solid when it turns to ice and the reason why it is in ice form is due to absence of heat. When the temperature is very low then the water freezes turning it to ice. If the planet is far away from the sun or at the lower end of the habitable zone then water turns to ice.

On the other hand if the distance of the planet relative to the sun is on the other extreme which is very close to the sun then water is superheated and evaporate. There will be no trace of water if the blazing heat of the sun can easily heat up water. This is one of the reasons why Mercury the planet closest to the sun is a lifeless planet. Interestingly the concept of the habitable zone is not really determined by the distance of the planet to the sun but also by the luminosity of the sun (Goldsmith & Owen, p. 402). This means that the power of the sun to melt ice is a major factor and not just the ability of the planet to keep it water in liquid form. This is because much of outer space is dark and cold. The absence and presence of the light of the sun is a more determining factor in maintaining water in liquid state.

According to experts the luminosity of the sun is the reason why habitable zones can be expanded or reduced. The higher the energy of the star then the greater is the habitable zone. This phenomenon was highlighted even further by the following statements:

If we apply the concept of a habitable zone to all stars in the Milky Way, we naturally find that the more luminous stars have the larger habitable zones. The stars’ greater energy output per second enlarges both the inner and outer boundaries of the habitable zone. A cook K or M star, far less luminous than the sun, will have a habitable zone smaller than the orbit of Mercury….(Goldsmith & Owen, p.403).

This habitable zone is therefore fixed, the propensity for life is determined not just by the size of the planet or other features but by its relationship to a sun-like star that gives light and regulates temperature. In order to completely understand the favorable position that one can find the planet Earth, astronomers revealed the extremes in temperatures on the outer edges of the habitable zone and they said that on the interior closest to the sun:

…the temperature rises above 100 degrees Celsius, and on the outside by the vast volume in which the temperature never rises above approximately 0 degrees Celsius. For a star like the sun, the habitable zone extends from about 0.85 AU, well outside the orbit of Venus, to about 2 AU, well beyond the orbit of Mars (Goldsmith & Owen, p.402).

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It is easy to see that while it is true that the habitable zone is considered beyond the orbit of Mars, the position of the Red Planet is not very ideal of living things to thrive as evidenced by the absence of life. Furthermore, repeated visits to the planet using space probes and even rovers that landed on it gave the general impression that Mars is a lifeless planet. This simply means that as one considers the relative position of Europa on the habitable zone then it is unlikely that water can stay liquid for long in order to support life.

Extraterrestrial Life

When the Voyager and Galileo spacecraft that were sent to observe Jupiter took pictures of the surface of Europa, scientists back on Earth were astonished to discover that there could be evidence of large plates of ice that broke apart and moved away from each other and they even added by way of explaining the unusual surface markings of Europa: “The easiest way for these movement to occur is if the plates are floating on water, just like ice floes that fracture and shit in the polar seas on Earth. If the plates can be fit back together like a jigsaw puzzle, with their edges matching up neatly, it will provide strong evidence that the material beneath them was once liquid, or at least warm, slushy ice (NASA CIT, p.1). This is the reason why they are excited to go in there and finally land a rover and determine once and for all the truth beneath Europa’s atmosphere is really because the spacecraft Galileo was only able to take pictures far away from the surface.

Those who wanted to believe that there is extraterrestrial life on Europa were given a major boost when scientists discovered that life can exist without light. In the past it was considered impossible to support life without the direct or indirect contribution of the sun but when man was able to develop and perfected the use of highly-sophisticated and highly-maneuverable submarines it is now possible to go even deeper into areas of the Earth’s oceans where sunlight cannot penetrate (Fischer,190). After a series of experiments and research underwater scientists were able to prove that there are life forms deep into this planet’s oceans that are flourishing in the complete absence of sunlight (Fischer, p.190). And the explanation given was that there were volcanic springs that provide the necessary nutrients and minerals needed by fish, crabs and even worms that live in that supposedly inhospitable environment (Fischer, p.190). It does not take a stretch of the imagination to consider the possibilities of life in Europa.

Aside from the possible presence of liquid water on Europa scientists are also making the assertion that the interaction of the moon to Jupiter has created what they call as “tidal heating” and the tremendous forces that has been applied to Jupiter’s satellite is enough to heat the frozen ice and therefore turn it into liquid (NASA, CIT, p. 2). In addition it can also be hypothesised that comets had crashed into the surface and as a result there is a great possibility that these comets had brought with the basic chemicals needed to support life (Fischer, p.191). This has fueled the desire to send a mission to Europa as soon as possible.

Desperate Need to Believe

It must be acknowledged that indeed it is possible to discover extraterrestrial life forms on Europa, however it must be said with much caution knowing very well the intricate balance of life’s necessities needed to be present in order to have a planet just like the Earth. There are so many requirements that in one glance absent in Europa. For example Europa is slightly smaller than the Earth’s Moon (Pater, p.193). This has tremendous implications because even a grade school student is aware that the Earth’s Moon does not have enough gravitational force to hold on to an atmosphere that is essential to support life.

Water is not the only ingredient necessary for life. The moment life is formed it has to be protected and nurtured from harsh elements coming from outer space. The atmosphere is the one that screens out harmful radiations. There is not even clear proof that Europa has a viable atmosphere ready to sustain whatever life form was present in the very beginning. There is also the absence of the real effect of the size of Jupiter. No one knows if the strong gravitational pull of Jupiter is beneficial or detrimental to life. One can argue that Europa is not only a place hostile to life but a heavenly body that is so much unlike Earth that if one will take out the possibility of liquid water then no one will even dare begin the discussion of the possibility of extraterrestrial life on this Jovian Moon.

Based on pictures taken by Galileo one can see that the surface of Europa was marked by a very powerful force, as if a giant baby scribbled something on it according to one clever writer. But in a scientific way of looking at it there is indeed one acceptable explanation which is the movement of heavy objects aided by water just like heavy ice floes or icebergs would break and float and move around in the arctic. Looking at the behavior of the planet Earth this one good way of explaining the “scribble marks” that one can find in Europa. However, there can be other explanations as to why these marks are present in the said Jovian moon.

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It was pointed out earlier that the habitable zone as described by scientists can reach beyond Mars. However, this can be read as a mere estimate and even as the boundary, the extreme part of the habitable zone. This assertion is backed by evidence of two lifeless planets side-by-side the planet Earth. If indeed Venus and Mars are still located in the same zone that can support life then at least there should be evidence of ancient life forms that used to thrive in the said planets. Even if these organisms died a long time ago then at least there should be remains. But there is none.

If it has already been proven that the atmosphere and the circumstances surrounding Venus and Mars could not support life, then, how is it possible to even consider life on Europa a moon that is farther from the sun than Mars? Depending on which group is asked the answer differs with regards to the certainty of having water on Europa. In a very harsh criticism one commentator said, “People tend to see on Europa whatever they are used to seeing” (Greenberg, p.229). Therefore the basis for understanding it is dependent on how people see scientific phenomenon on Earth. But it has to be made clear that Europa has an alien environment much different from what one can see on Earth and it has to be acknowledge that how elements and chemicals behave on Earth could not be said to be the same on Europa.

For those who are so eager to jump on the bandwagon that there is the possibility of extraterrestrial life on Europa caution is needed. Although there belief is rooted in one fundamental fact that there is water on Europa and this is a good start although a path that is still riddled with problems for water is not the only thing needed to support life. Lost in the discussion is the probability that the estimates are all wrong and just like Mars the scientists and space explorers will find their hopes dashed against a lifeless piece of rock that is too far away from the ideal habitable zone that it is just impossible for even a single bacterium to survive, even for one second.

Everyone it seems is caught up in the excitement that it is not common to hear the admission that a “lander” or an equipment that can land on the surface and gather samples can be launched so that scientists can provide what some scientists call as “the ground of truth” (Silber, p.1). This is because until an unmanned robot can land in Europa much of what is known about the planet can be considered pure speculation up until a mission can be sent out there to retrieve physical evidence. In one honest assessment one scientist remarked that: “It is not certain if there is a liquid water ocean on Europa at present” (Hamilton, p.1). It has remained a theory up to this time.

Going back to the discovery of life forms that exist in a very inhospitable environment such as the deepest parts of the Earth’s oceans, evidence has surfaced that can dash the hopes of those who believe that extraterrestrial life forms is possible even in the toughest of space environs. But those who pin their hopes using the aforementioned discovery of life in the deep oceans where the absence of sunlight was not hindrance to the flourishing number of fish, crabs, and worms in there are now in a more desperate situation because scientists discovered something else. In 1999 when biologists looked at the chemistry that exist in that level where sustenance was only due to volcanic springs, they also discovered that: “…the Earth’s oceans are only hospitable for life because they are constantly supplied with oxidants from the upper oceans…” (Fischer, p.192). This is a tremendous reality check for those hoping against hope that life can be discovered in Europa.


It is good to hope that there could be extraterrestrial life forms present in Europa whether in its recent history or ancient past. This is because of evidence that water exists in the surface and even the sub-surface of Europa. However, it was also made clear that water is not the only requirement needed to support life. There is the need for liquid water which is the universal solvent and the means of transport in the aqueous world of living cells. This is only possible if the planet or in this case Moon is within the habitable zone where a sun-like star can melt water and maintain it in a liquid form to be used by organisms – animals, vegetation, insects and even microbes. These things are not present in Europa. At this point life is almost impossible to exist there.


Goldsmith, Donald. The Search for Life in the Universe. CA:University Science Books, 2002.

Greenberg, Richard. Europa: The Ocean Moon: Search for an Alien Biosphere. UK: Springer, 2005.

Hamilton, Calvin. “Europa.” n.d. Web.

Hays, J.D. “Water: The Vital Fluid.” Columbia University. n.d. Web.

NASA. “Europa: Jupiter’s Icy Moon.” Jet Propulsion Laboratory California Institute of Technology. n.d. Web.

Pater, de Imke. Planetary Sciences. UK: Cambridge University Press, 2006.

Silber, K. “Target Europa: Ambitious Plans Aim for Jupiter’s Ocean Moon.” n.d. Web.

Ulmschneider, Peter. Intelligent Life in the Universe. UK: Springer, 2006.