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KBN-14-001May 14, 2014

To: Distribution

From: T. J. Ingram

Subject: 2014 Mentor Student Project

Enclosure: Into the Depths of Europa

During my time at The Johns Hopkins University Applied Physics Laboratory (JHU/APL), I conducted research on Jupiter’s moon Europa and its possible sub-surface ocean. I conducted qualitative research by analyzing data and statistics obtained from the joint Jet Propulsion Laboratory and the JHU/APL Pluto probe, New Horizons, and the recent discovery of Europa’s atmospheric water vapor. Mentor Tom D. Milnes assisted in the editing of my research paper.

T. J. IngramMentor Student

TJI/pjw

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Into the Depths of Europa

Introduction

The Solar System is full of surprises and mysteries. Despite the beauty and variety of the planets and their moons, there are many factors that prohibit the development of life outside a narrow band including Earth. In the past, scientists thought it nearly impossible for any organism to develop, let alone survive, outside the safety of this little blue planet. But as it turns out, life could actually be developing right now on faraway Europa. By further understanding the geology and possible biology of Jupiter’s moon of Europa, scientists can determine the best course of action to find life on or beneath its surface.

Discovery

The famed astronomer Galileo Galilei discovered the moon Europa in 1610. Using a 20x power refracting telescope, located at the University of Padua in Italy, he observed the planet Jupiter for days. Initially, Galileo couldn’t differentiate Europa from its sister moon, Io, and both were recorded as a single point of light. Later research established that they were independent orbiting satellites. Like all of Jupiter’s moons, Europa was named after a lover of the Greek god Zeus who was courted by Zeus and declared queen of the Greek island Crete. Some 363 years after Galileo’s discovery, the NASA probe, Pioneer I, became the first spacecraft to analyze the surface of Europa. While analyzing Europa, Pioneer discovered a thick sheet of ice encasing the moon. Many scientists speculated that Europa could

harbor a subsurface ocean but couldn’t provide further hypotheses due to limited data. It wasn’t until 1979 that the Voyager 1 conducted a fly by of Jupiter and detected readings that suggested a large body of liquid beneath a thick layer of ice – one that could potentially harbor life.

Jovian Moons

Europa is one of the most geographically complex satellites in the solar system. The moon orbits the largest known planet in the galaxy and is accompanied by the widest assortment of sister moons. The largest satellites, also known as the Jovian moons (Stevens), consist of Io, Europa, Ganymede, and Callisto. Ganymede is Jupiter’s largest moon and the largest in the solar system. Callisto is the furthest moon from Jupiter and is speculated to have scattered oceans beneath its surface (Stevens). Io is the closest Jovian moon to Jupiter (217,000 mi away) and is the most geologically active body in the solar system (Stevens). Due to its close

FIG. 1: Frederik de Wit’s visual depiction of Europa in Nova et accurata totius Europæ description (New accurate description of Europa)


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proximity to Jupiter, Io is orbitally locked, one side always facing the gas giant. This creates an orbital effect that occurs on Earth called tidal flexing. Io is constantly stretched and relaxed by Jupiter’s immense gravity which creates a large amount of friction and heat internally (Lemonick). The effect has created over 400 active volcanoes on Io’s surface, some taller than Mount Everest, resulting in a thin atmospheric layer consisting mainly of sulfur dioxide SO2

(Lemonick).

Geography

Europa has a large variety of surface features but is considered to be the one of the smoothest objects in the solar system. On a smaller scale, Europa’s equator has been theorized to be covered in 10-meter (32 feet) tall ice spikes called penitents---caused by direct sunlight melting vertical cracks (Tate). Europa’s surface is entirely comprised of ice and rock similar to that of Earth’s glaciers. The crust is speculated to be around 6-19 miles thick and acts like tectonic plates pushing and colliding with one another (Dodd). Europa is in a locked

orbit with Jupiter like Io, so it also experiences tidal flexing which is responsible for the active movement of ice sheets (Tate). Tidal flexing also creates a unique series of dark bands called lineaes that crisscross the entire planet and can be seen from space. The lineaes are large portions of the ice crust colliding and grinding with each other (Dodd). The lines could also have been produced by a series of eruptions of warm ice as the Europan crust spread open to expose warmer layers beneath (Dodd). Because of Europa’s ever-changing surface, it has relatively few impact craters. Many craters are immediately filled with water from Europa’s deeper layers then freeze (Stark). Europa’s ice sheet movement also melts surface ice, which could create small subsurface water lakes and perhaps a large ocean deeper from the surface. These bodies of water will sometimes eject large amounts of water vapor through geysers into the atmosphere, which then stay there.

On 12 December 2013, NASA announced, based on studies with the Hubble Space Telescope, that water

FIG. 2: Solid = no central peak, Open with solid center = central peak, Nested ring = multiring basins. Central peaks in craters consist of deeply buried material uplifted immediately after impact. If the impactor penetrates through the ice layer, a central peak will not form.


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vapor plumes were detected on Europa. Two geysers located within Europa’s southern hemisphere ejected these vapor plumes and could possibly be still active. If there are active water pockets close to the surface then there is a possibility of a larger body of water deeper in Europa’s ice crust.

Past Observations

When Galileo observed Europa over 400 years ago, he found it hard to determine its size and color because of the amount of sunlight being reflected off its surface. By the 70’s, thanks to the Pioneer 10 and 11 space probes, it was generally understood that Europa behaved like this because of the vast amounts of ice covering its exterior. The probes captured the first up close images of Europa that confirmed the presence of ice but not to what extent. More information about Europa wasn’t obtained until 1979, when the Voyager deep space probes conducted a flyby of Jupiter and the Jovian moons. The probes took more detailed images of Europa’s icy surface that sparked the scientific community’s interest as a possible place to harbor life. Scientists

began to theorize that due to Europa’s eccentric orbit and orbital resonance with the other Galilean moons, it could be going through tidal heating. If the ice on Europa was thick enough, and the forces acting upon it were strong enough, the surface ice could melt and produce a large body of water underneath.

Rediscovery

Because of the limited amount of information received from the Voyager probes, scientists were limited in advancing the state of knowledge about Europa. The United States was also beginning to cut funding intended for NASA because its main competitor, the USSR, was fading by the end of the cold war (Renstrom). This all changed when NASA launched its latest probe Galileo to orbit the gas planet Jupiter. Galileo was an unmanned spacecraft sent to orbit and analyze Jupiter and its four largest moons. Galileo possessed the most accurate and detailed instruments at the time along with a high-resolution camera (Melosh). The data and images were better than what was gathered during the Voyager missions and revealed more of Europa than before. Europa’s ice covered twice as much area as previously thought and were lined with odd patterns called lineaes (Melosh). A faint magnetic field was detected emanating from the moons surface. The existence of the induced magnetic moment requires a layer of a highly electrically conductive material in Europa's interior. The most plausible candidate for this role is a large subsurface ocean of liquid saltwater (Melosh).

FIG. 3: Water plumes observed orbiting Europa. White indicates higher concentration of water and most likely location of ejection

FIG. 4: Shows that the magnetic signature required an ocean within ~175 km of the surface of Europa, with a minimum required conductivity of ~ 72 mS/m and magnetic amplitude > 0.7.


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Sub-Surface Ocean

If a subsurface ocean did exist on Europa, it would be one of the most unique surface features in the solar system. The ice sheet that is most likely covering the ocean is very thick mixture of ice and rock that encases another 3 km layer of frozen ice. The crust layer is also exposed in specific areas on the surface but is slightly thicker due to vacuum exposure (Adams). It is predicted that the outer crust of solid ice is approximately 10–30 km (6–19 mi) thick, including a ductile "warm ice" layer (Melosh).

A

water sphere of Europa’s ocean would have a diameter of 1,090 mi, while Earth’s would only be 860 mi (Greenwald).

Europa receives a deadly dose of 5.4 sieverts of radiation from Jupiter compared to 0.0014 sieverts on Earth. The ice sheet would most likely absorb a majority of the radiation and prevent it from entering the oceans. A thin stratosphere separates the liquid water and the ice shell crust. The stratosphere contains stably stratified water which is at the freezing point, and therefore buoyant. If the water is warm, it would explain extensive geological evidence for melt through events (Melosh). This occurs when floating ice randomly sinks or breaks off from a large portion of ice. The water has strange thermo physical properties that


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make the surface ice freezing temperature different from the ocean. Europa’s overall density of 3.02 gm/cm3 indicates that the planet is mainly composed of silicates, which contain radioactive heat producing elements (Melosh).

Life on Europa

According to many scientists, Europa has the greatest probability of any outer body in the solar system to support life. Although Europa has a good area for life to live, there are a great many other building blocks needed for organisms to properly grow.

For all observed life to develop, it needs a consistent source of energy and specific chemical compounds. For a complex organism this includes sunlight for vitamin D, water, and proteins. All organisms begin in their simplest form which requires a substantially smaller amount, the most important being heat. The surface of Europa

has an average temperature of -276o F, which is virtually impossible for life to survive in. Underneath the ice is surprisingly warmer, the temperature theorized to be only around -50o F. This would be possible by the Tidal flexing effect on Europa, which could be warming the moons core and mantle. Europa could also produce heat from the decay of radioactive elements within its interior. Europa is made primarily of silicate rock as are the majority of moons planets in our solar system. From what data scientists have gathered over the past 50 years, Europa does naturally posses a majority of the needed chemicals for life to develop. Some critical compounds that are missing, however, are the element sulfur and phyllosilicate minerals. Because Europa did not obtain these compounds during its development, the only way for it to get them is by a foreign source. Europa’s sister moon Io is the only moon with active geological activity and will often spew large amounts of sulfur and sulfur dioxide out of its atmosphere. Because of how close Io orbit is (around 151,781 miles) to Europa, clouds of sulfur have been confirmed to land on the surface. There is also a possibility that asteroids carrying phyllosilicate clay-like materials have crashed onto the surface and entered a shallow lake with liquid water. In fact, there have been recent discoveries of these “clay-like” materials near the edges of older impact sites that were filled with a fresh sheet of liquid water. If the sulfur or clay found a way into the ocean, there is a definite chance that some form of life exists there.

Parallels to Earth

The chances of life on Europa seem slim, but there are similarities it shares with the Earth. Many scientists believe that

FIG. 5: A function of thickness that shows the melting-point viscosity of ice while calculating heat production and heat flow through the ice crust


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foreign objects like comets and asteroids brought the first bacteria that grew on Earth.

The water on Europa is covered by a thick shell of ice and is not open like Earth’s oceans. So the likelihood that an asteroid entered Europa’s oceans is very slim. There are, however, impact craters on the surface that are filled with fresh linings of ice, which would have to be near a source of water. Almost all life on Earth needs sunlight to survive. Because the thick layer of ice covers Europa’s oceans, it is impossible for light to make it to the water. This is similar to the polar ice caps of Earth. In Antarctica, scientists have uncovered subsurface lakes of water that are estimated to be over 100,000 years old (Scambos). The research team drilled into the sub glacial lake, named Hodgson, which was covered by 3-4 meters of ice using thermal ice penetrators.

These lakes haven’t been exposed to air in centuries but somehow hold traces of prehistoric life. The mud found at the bottom of the lake served as a time capsule and preserved DNA samples of microbes (Scambos). The samples confirmed that microorganisms could survive using a

variety of chemical methods without the need of oxygen or light (Scambos). Some areas of the Arctic Circle are completely cut off from sunlight and also have organisms thriving in below freezing temperatures. Scientists have called these resilient organisms Extremophiles.

Extremophiles

Extremophiles are organisms that can thrive in environments extremely hostile to most living things. There are radioresistant Extremophiles that survive near high levels of radioactivity. There are also thermoacidphiles, Extremophiles that prefer near–boiling acidic water like the Old faithful Geyser in Yellow Stone National Park (Cavicchioli). The newest forms of Extremophiles were found in a -20o C, 36-meter deep, salty arctic lake (Cavicchioli). These Halophilic Extremophiles can survive in below-freezing temperatures and consume proteins in the water as well as sugars like glycerol, by-products of algae living in the upper waters of the lake. These Extremophiles have been through extensive gene swapping, exploiting niches while staying independent of one another. Each Extremophile is slightly dissimilar at different levels and are thus identified as separate species. Halophilic Extremophiles grow very slowly, only producing six generations a year (Cavicchioli). The Extremophiles in Hodgson have the ability to grow under extreme cold and salty conditions similar to environments speculated to be on Europa.

There have also been organisms found in the Earth’s Arctic Circle under thick layers of ice. They survive by absorbing thermal energy from underwater vents on the bottom of the ocean floor

FIG. 6: Scientists drilled approximately 2.2 miles (3540 meters) through Lake Vostok and discovered organisms residing


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(Lemonick). Hydrothermal vents are fissures in a planet's surface from which geothermal heated water is ejected. They are commonly found near volcanically active places, areas where tectonic plates are moving apart, ocean basins, and hotspots (Lemonick).

Life near vents

Geothermal vents would be likely found at the bottom of Europa’s sub-surface ocean. The internal activity could be possible because of the moon’s locked orbit with Jupiter. The stretching and compression by Jupiter’s gravitational field would create internal heat and geological activity similar to the moon Io.

Some of these vents spew soot and other minerals that feed organisms and create complex biological communities around them. Shrimp, tube worms, plankton, and bacteria thrive near these types of vents, completely independent of the surface as well as sunlight on Earth (SETI). If all of these circumstances are possible on Earth and Io, there is quite a possibility that they could be happening on Europa (SETI). If they were, the only way to find out would be some form of exploration or detailed analysis of Europa.

Top Location

Europa is considered by the scientific community to be one of the top locations in terms of potential habitability of hosting extraterrestrial life. Mars used to hold this title but due to recent robotic explorations, its surface has been deemed inhospitable for well over millions of years. If this is the case, then why do space agencies like NASA keep sending probes and rovers there? There are lots of small factors like public interest and media attention but the most significant one is cost. NASA has been the leading innovator in civilian aeronautic and aerospace research since the fall of the Soviet Union in 1991. But since the end of the Apollo moon mission, public interest in space exploration had dipped significantly. Because of this dip of interest, the United States has been cutting NASA’s spending budget significantly to the point that they can only pursue a few projects a year.

Exploration

If scientists want to explore Europa in search of life, they will have multiple methods to do so. Nearly all planetary

FIG. 7: Part of a 360°C black smoker chimney of the Endeavour Hydrothermal Vents in Vancouver Island, Canada. Tube plants and other organisms can be seen taking residence


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exploration missions have had some sort of probe or orbiter sent prior to any landings. Before NASA’s Curiosity rover landed on the surface of Mars in 2012, there had been a great deal of data gathered from the dozens of unmanned spacecraft missions. This information was critical in selecting the proper time and location to land any probe onto the surface. If researchers want to land a rover, there must be a reconnaissance mission beforehand.

There have been a few orbital fly-bys of Europa in the past including the Pioneer probes, Voyager 1 and 2, and finally the Galileo probe, which carried out the most recent and detailed analysis of Europa. All of these spacecraft analyzed Europa as a secondary objective, however. There have never been any probes specifically dedicated to studying Europa. NASA has proposed a concept mission called the Europa Clipper that is set to launch sometime in 2025. The Europa Clipper would orbit Jupiter but make dozens of close flybys of Europa, using a variety of science instruments to study the moon's ice shell, subsurface ocean, and maybe the water cloud ejected by Europa’s geysers.

There have been many proposals for landing on Europa. The best way to analyze

a surface is to actually be on the surface. Scientists have landed plenty of probes on the Moon and Mars. Doing the same for Europa would provide invaluable information. If a probe were going to be developed, it would most likely be immobile because of the harsh and steep terrain that Europa most likely has (Madden). The stationary probe would most likely land in or near one of the impact craters because of the possible clay deposits and isolated water pockets (Madden). It could create a chemical composition mapping of Europa to find out what Europa is made of in detail. The Lander could also possess a small drill to analyze any small lakes found.

The main goal of exploring Europa is to confirm the possibility of extra-terrestrial life. Scientists can speculate as much as they want but the only way researchers can confirm life is to explore the subsurface ocean beneath the ice. This explorer would probably be the size of a small torpedo (Hsu). A radioisotope thermoelectric generator would power the probe; a small nuclear source could be installed around the size of a soda can. This could power the system for more than 2 years without the

FIG. 8: Europa Clipper would conduct detailed reconnaissance of Jupiter's moon Europa and would investigate whether the icy moon could harbor conditions suitable for life.

FIG. 9: Europa’s ocean is covered by 16 miles of ice crust. An explorer would need to travel through ice in order to enter water


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need of sunlight (Jiang). The explorer would have to be mounted onto a lander which would also have to possess a drill. The drill would move through the ice with the explorer inside or behind it and communicate though a fiber optic cable (Nelson).


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Lack of Funds

Cost is one of the main issues when proposing a scientific research process project. Many research teams acquire funding by an approval process through some sort of administrative body. In terms of NASA, a scientist must convince an approval board that their project will make best use of NASA’s limited resources. During the space race, NASA had an annual budget of almost five billion dollars, but this has dropped over three billion dollars as of 2012. Because of the lack of government funding, NASA has had to prioritize resarch projects and limit the amount of space missions.

Costs and Challenges

The reason why exploring Europa is particulary expensive is its great distance from Earth. Mars has been the focus most recently because of its relative proximity and public fascination with it. Europa represents a new research horizon for scientists. Because of Europa’s thick ice, a melt probe would have to be developed that could melt or cut through the ice. Another challenge would be communicating with an ocean explorer. Since the ice is nearly 16 miles thick, a long fiber cable would have to be developed and sent to Europa. Developing such a cable could cost more than the probe itself and transporting it to Europa would not be cheap.

Best Option

In order to explore Europa with acceptable risk, a step-by-step approach would be needed. First, scientists would need to send some sort of reconnaissance satellite to Europa in order to analyze its surface, confirm the presence of the ocean, search for possible landing sites, and be a relay point for communications. This mission could fly through the plumes of water that are being ejected by Europa’s geysers and analyze it for organic material. If the subsurface ocean is confirmed, the next step would be to send a lander containing the melt probe and the AUV. The lander will have to be smart enough to land in rough terrain without being externally controlled. It would take weeks for the melt probe to make its way to the ocean stopping when it reaches the water to relaese the AUV which would automatically inspect the water for life.

Conclusion

Europa is still a very mysterious planetary body. A majority of the current data is from a 40 year old defunct probe. There also isn’t a map of Europa’s surface. This makes sending a lander first nearly impossible. The largest challenge would be achieving the required sophistication at a reasonable cost. If an ocean explorer was sent, the mission would become the most complicated and greatest robotic achievement in history. A mission with such a high risk of failure might be terrifying to some in the scientific community. Obstacles notwithstanding, the discovery of life on Europa would revolutionize biological and planetary sciences and is worth pursuing.


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Europa Mission Concept


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FIG. 10: Reconnaissance probe would have an elliptical orbit of Jupiter and analyze Europa for 5 days every 3 months.

http://www.jpl.nasa.gov/missions/europa-clipper/

FIG. 11: Jupiter’s closest Jovian moon, Io, has extreme volcanic activity making it the most geologically active object in the Solar System. It releases sulfur that could enter Europa’s oceans and build life.

https://solarsystem.nasa.gov/planets/profile.cfm?Object=Jup_Io

FIG. 12: Lander would include an orbiter and lander. Orbiter would orbit Europa and send data back and forth from Earth. The lander will pose a probe that will melt through the ice 20-mile ice crust in a couple of weeks.

http://www.iki.rssi.ru/conf/2009elw/

FIG. 13: Europa has multiple geysers on its equator, which recently ejected plumes of water. These water plumes coated Europa with liquid water for weeks which could be analyzed for organics by a probe.

http://www.nasa.gov/content/goddard/hubble-europa-water


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FIG. 14: Europa is covered with unique surface features called lineae’s, which are caused by its tidal flexing. These lineae’s act as tectonic borders and would be the best landing site for a lander.

http://www.lpi.usra.edu/resources/outerp/euro.html

FIG. 15: When the melt probe reaches the ocean it would release an autonomous underwater vehicle (AUV) that would explore the ocean and search for life. This explorer would return to the probe to recharge and send back data.

http://www.imtp.febras.ru/ anpa_.html


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References

Adams, Henry. “Life on Europa? Subsurface Ocean Found on Moon of Jupiter” Geology. Geology, 11 August, 2012. Web. 23 Sept. 2013

Tate, Karl. “Jupiter’s Icy Moon Explained” Space. Tech media Network, 1 August 2013. Web. 26 September, 2013.

Dodd, Haldane “ Facts and figures on aviation” ATAG. ATAG, Mar 14 , 2012. 17 Nov 2012.Fecht, Sarah. "Hubble Spots Water Plumes on Europa." National Geographic. National

Geographic Society, 12 Dec. 2013. Web. 13 Dec. 2013.

Melosh, H. J., Ekholm, A. G., Showman, A. P., Lorenz, R. D. "The Temperature of Europa’s Subsurface Water Ocean." Europa’s Stratosphere (2003): 1-12. Print.

Schulze-Makuch, Dirk, and Louis Irwin. "Alternative Energy Sources Could Support Life on Europa." Transactions American Geophysical Union 82.13 (2001): 1-3. Print.Scambos, Ted. "Life Found in the Sediments of an Antarctic Subglacial Lake." Phys. Phys, 10 Sept. 2013. Web. 12 Nov. 2013.

Lemonick, Michael. “A living Ocean on a Jovian Moon?” TIME. TIME Inc., 15 March 2013. Web. 26 September, 2013.

SETI Institute. How Might Life Evolve on Other Worlds? Portsmouth: Teacher Ideas, 1995. Print. Life in the Universe Series 1.

Cavicchioli, Rick. "Sub-zero Heroes: Extremophiles Call Salty Antarctic Lakes Home." The Conversion. Conversion trust, 30 Sept. 2013. Web. 21 Oct. 2013.

Madden, Amy. "UT Scientists Design Lander for Jupiter’s Moon Europa." The Alcalde. U of Texas at Austin, 8 Aug. 2013. Web. 18 Oct. 2013.

Cowen, Ron. "The Whole Enceladus." SCIENCE NEWS 6 May 2006: 282-84. SIRS Issues Researcher. Web. 25 Oct. 2013.

Hsu, Jeremy. “Tiny Submersible Could Search for Life in Europa’s Ocean” Astrobiology Magazine. AstroBio, 14 June 2013. Web. 26 September, 2013.

Nelson, Jon. Communicating with Curiosity. NASA Mars Science Laboratory. National Aeronautics and Space Administration, 4 Aug. 2012. Web. 22 Oct. 2013.

Manley, Justin. "What Are AUVs, and Why Do We Use Them?" National Oceanographic Data Center. United States Department of Commerce, 25 Aug. 2010. Web. 22 Oct. 2013.


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Renstrom, Joelle. "How to Convince the Public That We Need to Invest in Space Exploration." Slate. The Slate Group, 5 Jan. 2014. Web. 5 Jan. 2014.

Zeynali, Omid, Daryoush Masti, and Saeed Gandomkar. "Shielding Protection of Electronic Circuits against Radiation Effects of Space." Advances in Applied Science Research 3.1 (2012): 446-51. Print.

Klotz, Irene. "Space X Launches Thai Satellite Into Orbit." NBC News. National Broadcasting Company, 6 Jan. 2014. Web. 8 Jan. 2014

Cichon, Meg “Space X Falcon Launch with Hydrogen Energy” Chicago Tribute . Reuters, Apr 4, 2010. Web. 7 Jan 2014.

Cavicchioli, Rick. "Sub-zero Heroes: Extremophiles Call Salty Antarctic Lakes Home." The Conversion. Conversion trust, 30 Sept. 2013. Web. 21 Oct. 2013. <http://theconversation.com/ sub-zero-heroes-extremophiles-call-salty-antarctic- home- 18734>.

Into the Depths of Europa. Dir. John Greenwald, Jr. The History Channel. A&ETelevision Networks, 9 Dec. 2009. Web. 2 Oct. 2013.<http://www.history.com/shows/the-universe/episodes/alien-faces/342r9732ry37r2gr3>.

Mckay, Chris. "Titan: A Moon with Atmosphere." Astrobio. FirstGov, 27 Oct. 2005. Web. 14 Jan. 2014. <http://www.astrobio.net/ index.php?option=com_retrospection&task=detail&id=1755>.

Stevens, Michael. What Breakthroughs Are Enabling New Space Exploration? Discovery Channel. Discovery Communications, 1 Feb. 2009. Web. 11 Dec. 2013. <http://dsc.discovery.com/tv-shows/curiosity/topics/ what-breakthroughs-are-enabling-new-space-exploration.htm>.

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