Astronomy Online

Life on Europa - an Essay by Ricky Leon Murphy:

Seeing the frozen surface of Europa for the first time must have been an extraordinary event. Telescopic observation and Voyager data reveal what is to be a frozen water-ice surface. Could liquid water exist below this surface? Liquid water is an essential ingredient for life, and water seems to be located in more and more places as we explore the solar system. Data from the Galileo probe indicate what might be some geologic activity on Europa, and with activity comes the possibility of organic material. Meteorites like ALH 84001 raise the question that organic material may exists outside the Earth. Further exploration of Europa could prove that water and organic material exist under the frozen surface. Information gathered from Europa and its possible evidence of life can give us further insight as to how life on Earth evolved, and further advance our current knowledge of how the solar system formed.

Earth is a special case since life already exists here. We have an atmosphere that sustains life, and we see living organism in a variety of environments. The formation of Earth and its ocean of water are still not clearly understood, but the most accepted theory is water being introduced by comet impacts as our planet continued to evolve. With a predominantly carbon dioxide atmosphere and a liquid ocean – thanks to the size and location of Earth – atmospheric evolution was able to begin. Volcanic activity introduced carbon dioxide as the oceans absorbed the carbon dioxide to create carbon containing minerals (Beatty, et. al., page 187). With active plate tectonics and underwater volcanic activity, carbon material with water and methane – expelled by under water volcanoes – were able to evolve and form complex amino acids as shown by the Miller-Urey experiment (Freedman, pg 691). Carbon is capable of conglomerating into larger molecules, and as carbon material began to form more complex molecules, life was able to begin (Beatty, et. al., pg 690). Eventually, plant life evolved and began to absorb carbon dioxide and release oxygen in the atmosphere in a process called photosynthesis. Liquid water on Earth plays a key role since water is required for life. Water is a part of a living organism and is responsible for transporting and combing nutrients and controls metabolic break down and facilitates waste removal (Microsoft Encarta Reference Library 2003). This process is called hydrolysis.

It is commonly believed that comets provided the water on Earth. This seems to be the case since water is being found in surprising locations. In an effort to fill the gap of missing data left by the Magellan space probe of the surface of Mercury, radar imagery from Earth has discovered what appears to be water-ice within the craters of the north and south poles of Mercury (Beatty, et. al., pg 95). The Clementine probe scanning the surface of the moon has found similar water-ice on its poles (Beatty, et. al., pg 77). The polar caps of Mars are a familiar site, and with the sublimation of the frozen carbon dioxide during seasonal changes, the water-ice north pole is revealed (Freedman, pg 268, 269). A meteorite originating from Mars has shown to include some water, though not that much (http://www.jpl.nasa.gov/snc/nasa2.html). Comets have formed at the same time as the solar system, and comet impacts on the planetesimals were fairly common. These water-ice balls may show a higher deuterium level than the water here on Earth (Beatty, et. al, pg 335), however with water seen on other bodies as well as Earth lead to the speculation that water originated from this source. Enough carbon material could have also been introduced by comet impacts as well (Freedman, pg 690). These carbonaceous chondrites have shown the presence of enough carbon material to possibly allow the catalyst to begin the cycle of life. Europa, with a water-ice surface, has also been subjected to comet impacts as the other planets. The appearance of few impact craters today give evidence to some geologic activity (Beatty, et. al., pg 253).

Organic material does exist here on Earth deep in the ocean. However, new discoveries of previously unseen organisms thrive in locations where we would least expect them. Lithoautrophic organisms have been discovered near volcanic vents deep in the ocean where sunlight fails to penetrate (Beatty, et. al., pg 369). The volcanic vent provides the energy and carbon material. It was initially thought that sunlight was a key factor on the formation of life, but these organisms prove otherwise. More extreme environments have also revealed some strange life signs. Worm-like organisms deep in the Gulf of Mexico survive from the underwater source of methane and without sunlight. These organisms are dubbed “extremophiles” (Beatty, et. al., pg 368). Even more surprising is the recent discovery of organisms that do not need volcanic heat to survive, and live by processing methane instead of carbon dioxide or oxygen (http://nai.arc.nasa.gov/news_stories/news_details.cfm?ID=52). These hydrogen-oxide bacteria evolve and survive in temperatures of only 40C to 75C, far below the heat of a volcanic source.

The discovery of a meteor in Antarctica dubbed ALH 84001 has brought forth questions of the possibility of life from a source other than the Earth. While controversy surrounds this meteorite, proponents of ALH 84001 maintain the microscopic fossils of bacteria found on this meteorite originated from Mars. Skeptics have shown the microscopic bacteria resemble bacteria found under the ice of Antarctica (Beatty, et. al, pg 371, 372), and therefore was introduced on this meteor upon impact thousands of years ago. While the data remains controversial and inconclusive, this teaches us three very important lessons. The first lesson is life is possible (in this case on Mars) although the possibility is remote and unconfirmed. The second lesson is that scientific scrutiny plays a vital role in the evaluation of data. And the third lesson is to create a list of standards when evaluating the possibility of life. A standards organization can be organized to draw on disciplines such as medical science and research, pharmaceutical companies, and the biological sciences. These groups deal with life on a daily basis, and can provide valuable data in generating a list of standards. It is clear in the case of ALH 84001, contamination from an outside source is certainly possible. Every effort must be made to remove any outside influence, conscious or unconscious, when evaluating organic material. Gravity influence, heat, radiation, and bacteria from other sources could dramatically affect the outcome of data.

Recent Galileo data shows there is some internal heating emanating from Europa. With this heat as an energy source, the prospect of life becomes exciting. Such heating can be attributed to several sources, such as the normal decay of radioactive material; however, the majority of heating is thought to occur from tidal flexing as a result of Jupiter’s enormous gravity pull (Beatty, et. al., pg 254). Using the moon Io as a model, we see prominent volcanism as a result of this tidal energy from Jupiter (Beatty, et. al., pg 245). The same effects of tidal flexing may also cause volcanism on Europa, called cryo-volcanism (Beatty, et. al, pg 254). The friction heat caused by this flexing will also allow the water to remain liquid under the icy surface. The smooth surface and the presence of bulging and fractures point to some active geology that could indicate cryo-volcanism. Further evidence of cryo-vulcanism is present in the form of localized bulging, triple fracture bands and resurfacing (Beatty, et. al., pg 260, 261). Reddish material seen in photography from Galileo could indicate material from the mantle being stirred up in the presumed liquid ocean by the active geology. With a water-ice surface and the presence of a heat source, a liquid ocean almost seems very likely. Knowing that organic life can exist in some extreme environments and knowing that volcanism can release carbon material make the prospect of life on Europa more likely. Even more remarkable is the discovery of a tenuous oxygen atmosphere. This data provided by the Hubble Space Telescope (http://jpl.nasa.gov/galileo/europa/hst.htm) could be the result of liberated oxygen from the magnetosphere of Jupiter; however this new information is added to the list of questions to be answered by further exploration. With the Europa Orbiter scheduled to arrive in the year 2008 (http://www.jpl.nasa.gov/europaorbiter/EO_info.htm), our answers to the presence of liquid water and geological activity will be revealed. It is clear that given the questions of life Europa, further exploration is necessary.

Water is important to life. Life in our deep oceans should become a template in which we evaluate the possibility of life on Europa. Organisms can survive in extreme environments, and organic material in our solar system is available either by comet impact or active volcanism. With the possibility of a liquid ocean and the presence of internal heat, and evaluating the presence of life in our own deep oceans and recognizing alternate sources of energy and organic material, the possibility of life on Europa is likely. Further exploration will continue to answer our questions and may generate more questions to be answered. The key to unlocking the origin of life on Earth may exist deep in the sub-surface oceans of Europa. We may have a chance to witness the early stages of life that was once present on Earth millions of years ago. Only by continuing our exploration of our solar system will we begin to understand our own humble beginnings. However, great care must be given when evaluating the possible presence of life. Every effort must be made to scrutinize the results of exploration so controversy can be avoided.

References:

Beatty, Kelly J., Petersen, Carolyn C. and Chaikin, Andrew, ed. The New Solar

System. Cambridge: Sky Publishing Corp, 1999.

Freedman, Roger A. Universe 6^th Edition. W.H. Freeman and Company, 2002

Microsoft Encarta Reference Library 2003. 1993 – 2002 Microsoft Corporation

NAI Features Archive. “Life without Volcanic Heat.” Internet. 11 Jan 2002.

http://nai.arc.nasa.gov/news_stories/news_detail.cfm?ID=52

Public Information Office, Jet Propulsion Laboratory. “Europa Orbiter: Mission

At a Glance.” Internet. 11Sep 2002.

http://www.jpl.nasa.gov/europaorbiter/eo_info.htm

Public Information Office, Jet Propulsion Laboratory. “Hubble Finds Oxygen

Atmosphere on Europa.” Internet. 23 Feb 1995.