Chemicals of Europa

As we mentioned at the end of our previous blog post, there are certain chemicals we know Europa would need to have in order for there to be life.

Detection Of Chemicals

At first it may seem strange to be talking about the chemicals of Europa at all. To date, no probes have skimmed the atmosphere of Europa, let alone landed and taken samples for chemical analysis. Yet here you are about to read about the chemicals that are present. This is made possible by of one of the most basic tenets of quantum mechanics, namely the idea that electrons have quantized energy levels. This means that electrons can only exist in certain regions of an atom, with a specific energy inherent to that region. In order to move from one of these energy levels to another an electron must either emit or absorb a photon whose energy is the difference between the energy levels. The energy, and also color of a particular photon is determined by its frequency. Therefore, if you look at the light emitted by a heated substance, you will see distinct bands of colors indicating the electron transitions occurring. What makes this useful for identifying chemicals is that the energy levels that are available to the electrons and the transitions that occur are completely dependent upon the element or compound. Moreover, each unique compound has its own emission and absorption spectra, the features of which can be detected even amongst a whole moon full of chemicals nearly 400 million miles away. This method has discovered the presence of two important chemicals on Europa: oxygen and hydrogen peroxide.

Europa1

The Importance of Oxygen and Hydrogen Peroxide

The reason that scientists think that finding evidence of hydrogen peroxide and oxygen on Europa is important is because they are among the best oxidation agents known to exist. Oxidation agents are essential to every form of life that we know exists. They are most important because of their role in redox, or oxidation-reduction, reactions. In a redox reaction one compound takes electrons from another.  The compound that gains the electrons becomes reduced, and the compound that loses the electrons is oxidized. Examples of redox reactions include everything from the rusting of iron (where iron is oxidized and oxygen is reduced) to the reaction between glucose and oxygen.

Europa2

Respiration- Both Simple and Complex

Perhaps the most important redox reactions for living organisms are those involved in respiration. Just like all compounds, organic compounds, such as the proteins and carbohydrates that make up organisms, have energy stored in the bonds that hold it together. Taken as a whole, respiration works a lot like combustion, in which a hydrocarbon is oxidized and energy is realized in the form of heat. However, if fires were constantly starting in our mitochondria, we would have some significant problems. Fortunately, the process is broken into many steps, each of which releases a relatively small amount of energy. In complex multicellular life on Earth, this process is done through a series of increasingly powerful oxidizing agents known as the electron transport chain. The electron transport chain transfers electrons from the organic compound being brought down through a series of complex compounds until it ends up being captured by oxygen, the final electron acceptor.

Europa3

Water

Perhaps the most important substance for life to exist is liquid water. In the first blog post, we talked about how and why scientists suspect that there is liquid water on Europa. Now we are going to talk about why water in particular is so important.

Polarity

Anyone who knows anything about electronegativity can tell you that water is a polar molecule. The oxygen atom takes on a partial negative charge (denoted 𝛿-) and each of the hydrogen atoms takes on a partial positive charge (denoted 𝛿+). These partial charges allow water to dissolve countless polar and ionic solids, hence why it is referred to as the universal solvent. Most biological reactions will only happen if all of the reactants are in the aqueous state. There is a tendency for polar compounds to dissolve other polar compounds and for non-polar compounds to dissolve other non-polar compounds, and this allows for the easy storage of water. Non-polar molecules like lipids are used to form membranes in cells that are capable of retaining water.

Europa4.jpg

Water’s efficacy as a solvent is part of why it is so vital to life on Earth. All (known) living organisms contain liquid water in their bodies. Water is used to transport nutrients and other vital substances (e.g. glucose) to the areas of our body in need. Other compounds, such as salts are also transported via water. In most animals, blood forms the primary method of active nutrient transfer in the body, and blood’s ability to transport the nutrients depends on water’s solubility.

Hydrogen Bonding

Because water contains hydrogen atoms bonded to oxygen atoms, it contains in what is called “hydrogen bonds”, the strongest type of intermolecular force. This leads to a series of interesting and important properties of water. For one, each water molecule is strongly attracted to the other water molecules around it, making it hard for water molecules to break away and evaporate into the vapor phase. This gives water a relatively high boiling point (100°C) for such a small molecule. This means that it would take very serious changes in the environment to cause a phase change for large amounts of water. Hydrogen bonding is also responsible for water’s unusual property of having it’s solid phase (ice) be less dense than its liquid phase (water). The optimal bond lengths for the hydrogen bonds are actually greater than the distances water molecules usually are from each other causing them to expand as they freeze. This allows for the phenomenon of underwater oceans to exist because the less dense ice essentially floats on top of the water.  The ice basically thermally insulates the rest of the water from the surrounding freezing conditions. In Europa’s case, the ice acts as an insulating blanket, trapping the internal heat generated by Europa’s movement around Jupiter. This insulated layers allow for the possibility of a liquid ocean existing.

Europa5Europa6.png

Future

Future missions to explore Europa, like NASA’s proposed Europa Clipper aim to analyze the surface of Europa. The mission would launch a satellite to orbit Europa, performing repeated close flybys of the moon’s surface. Various scientific instruments would be used to analyze the surface and trace atmospheric composition of Europa. High-resolution cameras would also enable exquisitely detailed surface imaging of Europa’s icy outer layer. Additionally, there exists the possibility for radar to be included on the satellite, which would allow NASA to determine the depth of Europa’s surface ice.

Europa7

Advertisements

What Might Life On Europa Be Like?

Image From A Fictional Movie, Not Intended to Be Realistic

Hydrothermal Vents

 

Before speculating about what kinds of life could conceivably live on Europa, we should first talk about where it’s most likely going to be. At first, you might think that because life on Europa couldn’t possibly have access to adequate sunlight, there isn’t going to be any source of food for any potential lifeforms. However if you’ve been reading our blog posts from the beginning, you’ll know that Europa possibly has an underground liquid water ocean that stays liquid due to heat from its tidal interactions between Jupiter and the other moons. Because of this Europa likely has Plate Tectonics just like Earth. At the plate boundaries, magma can get exposed to the water creating incredibly hot hydrothermal vents.

On Earth

 

When hydrothermal vents are on land, they become better known as hot springs and geysers. However, we are more interested in the vents at the bottom of the ocean. The conditions around those vents more closely approximate the conditions that any life on Europa would have to endure than anywhere else on Earth. Despite the extreme pressures, heat, and complete lack of sunlight, biodiversity flourishes in these environments.

Bottom of the Food Chain

Despite having next to no energy from the sun, bacterial life surrounding hydrothermal vents flourishes. These organisms get their energy from Chemosynthesis rather than photosynthesis. Chemosynthesis is the creation of energy rich organic compounds using energy from non-organic chemicals rather than light. Chemosynthesis cannot one set of chemical equations like photosynthesis because there are many different types of it.

One of the very important forms of chemosynthesis here on Earth is Hydrogen Sulfide Chemosynthesis. This form of energy production is the source of most of the energy feeding the communities surrounding Earth’s hydrothermal vents.  Microscopic organisms like the Purple Sulfur Bacteria are capable of oxidizing the sulfur in hydrogen sulfide to elemental sulfur and forming glucose as described in the chemical equation below. This yellow elemental sulfur can actually be seen in cytoplasm of the bacteria

12H2S + 6CO2 → C6H12O6 + 6H2O + 12S

Methanogenesis on the other hand involves the reduction of the carbon in CO2 to methane and the oxidation of some of the hydrogen in hydrogen gas to water. Unlike hydrogen sulfide chemosynthesis, Methanogenesis is very common in less extreme environments. Bacteria that undergo methanogenesis are found everywhere from plants to the human digestive system. It is also considered by many scientists to be a very possible source of energy for life on Europa and might be able to explain the amount of methane in Europa’s atmosphere.

CO2 + 4 H2 → CH4 + 2 H2O

Infrared Photosynthesis

Another completely different way to produce energy at the bottom of the ocean actually relies on the same principles that life elsewhere does. As everyone knows, if you heat a metal enough, it will begin to emit red light. It turns out that it actually was emitting light the entire time just not in the visible spectrum. As the metal got hotter and more energetic, the energy of the light it emitted became higher in frequency, lower in wavelength, and more energetic.This phenomenon, known as blackbody radiation, occurs in all matter at all temperatures including heated water near hydrothermal vents. This water is still not hot enough to emit visible light. However, some species of bacteria, like green sulfur bacteria have adapted a method of photosynthesis that works off of infrared wavelengths, light that has too large a wavelength to see.

Large Organisms

With the bacteria converting just about any energy they can get their hands on into food, larger organisms are able to feed off of them creating complex ecosystems surrounding these hydrothermal vents. The same could be true of Europa, meaning that any kind of microscopic life could lead to much more interesting alien ecosystems. For instance the Giant Tube Worm that inhabit many of the hydrothermal vents have a symbiotic relationship with chemosynthetic bacteria that live inside a specialized organ in the tube worm. The bacteria then provide nutrients to the tube worm that would otherwise not be present at the bottom of the sea. While most of the animals inhabiting these depths of invertebrates like the tube worm, a community of eel’s has even been found near American Samoa.

 

Life on Europa

Europa

Europa

Europa

Europa, a moon of Jupiter, is thought to be one of the best bets for extraterrestrial life in the solar system. At first it seems crazy to think that something so far from the sun could possibly support life, yet there are numerous reasons to believe that Europa can do just that. However, to understand the nature of life on Europa, we must first review the origins and unusual circumstances of this moon of Jupiter.

Formation of Europa

The prevalent theory for the formation of the eight planets of our solar system (and any planets outside our solar system too) is called Nebular Collapse Theory. This theory states that in a protostellar nebula (a cloud of hydrogen, helium, and trace amounts of other elements that will one day form a solar system) a region of high density will begin to collapse in upon itself and, due to the conservation of angular momentum, rotate faster and faster as it collapses. While shrinking, due to a complex mixture of collisions, gravity, and gas pressure the nebula flattens itself into a disk. While the center continues collapsing and heating as predicted by the ideal gas law until it ignites into a hydrogen-fusing star, little conglomerations of silicates and metals close to the center and hydrogen compound ices farther from the center begin to form. These objects, called planetesimals, are the first stages of most things in the solar system, from tiny asteroids to the massive Jovian planets. Some of them are able to accrete mass through chemical bonding until they can hold themselves together gravitationally, and the most massive of these become the cores of planets. You can read some more about that topic here.

It turns out, while this is not how our Moon formed, the same mechanics are behind the formation of Jupiter’s major moons. Jupiter is so massive that when its planetesimal was gravitationally capturing hydrogen and helium gas, the gas cloud acted similarly to a nebula.

Nebular Collapse Theory

What do Volcanoes of Io and Oceans of Europa Have in Common?Europa is in a relatively crowded part of the solar. It is stuck in orbit around the second most massive object in the Solar System (after the sun) with a bunch of other massive moons (like Io and Ganymede) that may be considered planets or dwarf planets if they were to orbit the Sun instead of Jupiter. Europa is so close to Jupiter that there is actually a significant difference between the gravitational pull on the side of Europa facing Jupiter and the gravitational pull on the side of Europa facing away from Jupiter. This causes what is called a tidal bulge in Europa. Its sister moons also play a big role in Europa’s characteristics. This is because the three moons are in a 4:2:1 resonance which means that for every one orbit Io makes, Europa makes two, and Ganymede makes four. This forces Europa into a pretty eccentric (non-circular) orbit. An eccentric orbit means that there are times that Europa is fairly close the Jupiter and other times when it is farther away. This difference in the orbital radius causes the gravitational pull of Jupiter and the size of the tidal bulge to be variable. The periodic growth and shrinking of Europa causes heat to be generated due to friction and are thought to enable the existence of an underground ocean on this moons. These same forces called Tidal Heating cause Io (the first moon of Jupiter) to be incredibly volcanically active.

Illustration of Tidal Forces Acting on Europa

Note the first part of this video, from the Science Channel’s Into the Universe with Steven Hawking, where it describes tidal heating.

The Evidence

To some, even with the presence of tidal heating, the idea of a liquid water ocean so far from the sun seems implausible. However, this theory is backed up by data collected from passing Voyager and Galileo spacecraft. Perhaps the most readily observable, albeit difficult to quantify, evidence is the presence of scars on Europa’s surface that look a lot like cracks in a sheet of ice, exactly what they are theorized to be. These linae, as they are technically called, are indications of deformities in Europa’s icy shell, caused by the tidal stresses imposed on Europa’s not insignificant mass. Another important piece of evidence is the 2010 flyby of NASA’s Galileo spacecraft, which detected changes in Europa’s magnetic field, indicating the presence of a layer of an electrically conductive material, namely, an ocean of salt water.