1/1/02 Update: Recent Galileo images show what might be convection cells bringing material from deep within Europa to the surface. If this is in fact the case, it might be much easier to identify life on Europa then previously thought. Visit the Galileo project homepage at http://galileo.jpl.nasa.gov/ for the latest information.
The spots in this image could be convection cells bring material to the surface of Europa.
Europa, one of the moons of Jupiter, appears to be one of the few places that we might find extraterrestrial life in our solar system (the others being Mars and Titan, a moon of Saturn). What makes Europa such an attractive place to look for life is the possibility that it has liquid water and volcanic activity. Liquid water is essential for life on earth and is the most probable solvent for life elsewhere. Volcanic activity provides some of the heat necessary to keep the water on Europa from freezing and could provide important dissolved chemicals needed by living organisms.
The surface of Europa is covered with ice. NASA's Galileo space probe has recently sent back a number of high quality images of Europa's surface. These images hint at a layer of liquid water under the ice.
We will probably have to wait for one or more additional missions to Jupiter and Europa to verify the presence of liquid water and life on Europa. The planning for these missions is just getting underway. Current plans call for the use of radar to identify possible ice-water and water-rock interfaces on Europa and for the return samples of the surface ice. The mission, currently called the "Europa Ice Clipper," is scheduled for launch in 2001 and could return ice samples to Earth by 2009.
Europa's distance from the Earth and Sun and its thick layer of ice will make exploration difficult. However, discovering life on Europa would double the number of planets we know of with endogenous life. Even if no evidence of life on Europa is found, its exploration would provide a wealth of information about the chemistry and planetary physics of a very interesting body. Such information could help us better understand the atmospheric chemistry (with implications for global warming models), geophysics and other practical issues here on Earth.
Additional information is available from the following sources --
|Web Sites||Books||Papers & Articles|
The Astrobiology Web Page contains links to a number of astrobiology related sites. The Europa Revealed Web Page contains links to number of specific Europa related sites. Both of this sites are being kept more up to date than mine.
The Galileo space probe is current sending back the best images of Europa ever obtained. The latest information from the mission can be obtained from the NASA JPL Galileo Mission web site.
NASA has decided to extend the Galileo mission for two years. They're calling the extension the Galileo Europa Mission (GEM) and have created a web site describing it. NASA has also put together an Europa Fact Sheet
A collection of Europa images can be found on the Europa Page of Calvin J. Hamilton's Views of the Solar System project.
NASA's Exobiology Branch conducts ongoing exobiology research. The Exobiology Branch is part of the Space Science Division.
Extraterrestrial life in general and life on Europa are often mentioned in papers in Nature magazine and on the Nature web site.
Extraterrestrial life in general and life on Europa are often mentioned in articles in New Scientist and on the the New Scientist Planet Science web site.
If there is life on Europa, it will exist in an ice covered ocean and could cluster around hot springs in the ocean floor and resemble life forms known to exist under similar conditions on Earth. These life forms are described on the USGS web page Exploring the Deep Ocean Floor: Hot Springs and Strange Creatures.
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Anders Hansson. Mars and the Development of Life, 2nd ed. John Wiley & Sons ISBN 0471966061.
Paul Davies. Are We Alone? Philosophical Implications of the Discovery of Extraterrestrial Life. Basic Books, 1996. ISBN 0465004199.
Steven J. Dick. The Biological Universe: The Twentieth-Century Extraterrestrial Life Debate and the Limits of Science. Cambridge University Press, 1996. ISBN 0521343267.
Ben Zuckerman and Michael H. Hart, Eds. Extraterrestrials: Where Are They?, 2nd ed. Cambridge University Press, 1995. ISBN 0521443350.
Terence Dickison and Adolf Schaler. Extraterrestrials: A Field Guide for Earthlings. Camden House 1994. ISBN 0921820879.
Jean Heidmann. Life in the Universe. McGraw-Hill, 1992. ISBN 0070278873.
Emmanuel Davoust (Barbara Jachowicz (Translator)). The Cosmic Water Hole. MIT Press, 1991. ISBN 0262041146.
Arthur C. Clarke. 2010: Odyssey Two. Ballantine Books, 1984. ISBN 0345303067.
Arthur C. Clarke. 2061: Odyssey Three. Ballantine Books, 1991. ISBN 0345358791.
Arthur C. Clarke. 3001: The Final Odyssey. Del Ray, 1997. ISBN 0345315227.
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There are a number of sources of general background information on the origin and versatility of life. Chyba describes his model of impact delivery of volatiles to the rocky planets in "Impact Delivery and Erosion of Planetary Oceans in the Early Inner Solar System" (Nature 343:129-33 January 11, 1990). His conclusion is that it is that comet and asteroid impacts between 4.5 and 3.5 billion years ago could have delivered the water, carbon and nitrogen for Earth's biosphere. Cohen explains his views on alien life in "How to Design an Alien" (New Scientist 18-21 December 21/28, 1991). He develops the useful distinction between Universal and Parochial features of life forms. While I agree with his distinction, I would put a lot more features commonly found in life on Earth in his Universal category. Particularly, for intelligent, technologically capable beings. For example, I would expect any intelligent, technologically capable beings to be bipedal, have a head complete with a nose, mouth and two eyes (binocular vision), have arms and have hands with fingers (but quite possibly not 5 fingers on each hand). The October 1994 issue of Scientific American (Volume 271, Number 4) concentrates on life in the universe. It has a number of excellent articles on the subject. Richard Monastersky describes microbes that have recently been discovered living deep within the Earth in "Deep Dwellers" (Science News 151:192-3 March 29, 1997). Life on Mars and Europe might be similar to these hardy organisms. Michael Crowe scrutinizes the debate on extraterrestrial life in relation to religion, history, science and philosophy in "A history of the extraterrestrial life debate" (Zygon: Journal of Religion & Science 32(2):147-63 June 1997).
The idea that Europa and other ice-covered bodies in our solar system might possess an ocean of liquid water under a crust of ice may have first been proposed by John S. Lewis in his paper Satellites of the Outer Planets: Their Physical and Chemical Nature (which appeared in Icarus, vol.15, 1971). See Ralph Greenberg's History of Europa excellent web page at http://www.math.washington.edu/~greenber/EuropaHistory.html for more information.
Later, Reynolds, et al. ("On the Habitability of Europa," Icarus 56:246-54 1983) published an excellent paper that addresses the general requirements for life and examines possible thermal, solar and electrical energy sources for life on Europa. They estimate a possible biomass density of about 2 x 10-6 g/m2 based on solar energy availability. Ross and Schubert followed up on earlier work and concluded that under present conditions tidal heating is only marginally capable of maintaining a liquid ocean on Europa ("Tidal Heating in an Internal Ocean Model of Europa," Nature 325:133-4 January 8, 1987). Ojakangas and Stevenson published two very detailed models of the thermal and dynamic behavior of a ice shell on Europa ("Thermal State of an Ice Shell on Europa," Icarus 81:220-41 1989 and "Polar Wander of an Ice Shell on Europa," Icarus 81:242-70 1989).
More recent and accessible information on extraterrestrial life in general and life on Europa in particular include the following. Cowen's essay "Visions of Europa" (Science News 150:8-9 July 6, 1996) provides some background and an overview of the debate on life on Europa. The August 17, 1996 issue of New Scientist (Volume 151) focuses on the Martian meteorite ALH84001 and includes a side bar on page 10 by Justin Mullins on possible life on Europa. Crawford reflects on possible reasons why we have not already be connected by extraterrestrial aliens in his essay "Where are all the Extraterrestrials?" (New Scientist 152:52 October 5, 1996). The Galileo mission science team reports their initial findings the October 18, 1996 (Volume 274) issue of Science (starting on page 377) and these results are summarized by Richard Kerr on page 341 of that issue. Tyson (Neil de Grasse, not Mike) summarizes of the case of life on other planets and the search for extraterrestrial intelligence (SETI) in "Is Anybody (Like Us) Out There?" (Natural History 105(9):70- September, 1996). Chown describes Frank Tipler's controversial views on the implications of our lack of contact with extraterrestrial intelligence in "Is Anybody Out There?" (New Scientist 32-5 November 23, 1996). A collection of letters responding to Chown's article appear in New Scientist 152:80-1 December 21/28, 1996.
Williams, Kasting and Wade propose that there could be habitable moons around the recently discovered giant planets orbiting near by stars ("Habitable Moons around Extrasolar Giant Planets," Nature 385:234-6 January 16, 1997). Chyba comments on Williams et al.'s paper and discusses the current thinking on extraterrestrial life ("Exobiology: Life on Other Moons," Nature 385:201 January 16, 1997). Kerr describes recent Galileo data in "An Icy World Looks Livelier (Science 275:478 January 24, 1997). Powell discusses Europa, Williams et al.'s paper (and Chyba's comments) in Nature and Thomas Gold's discovery of microorganisms living deep in the Earth in "The Greening of Europa" (Scientific American 28-9 April 1997). Recent results from the Galileo probe on Jupiter's four Galilean moons are described in "Jupiter's Odd Bunch" (New Scientist 42-5 April 5, 1997). Results from the Annual Lunar and Planetary Science Conference in Houston are summarized in "Biology on Europa" (Science News 151:210 April 5, 1997). A short article including an image of Europa's icy surface showing features resembling those found in the Arctic Ocean on Earth appear in "An Ocean Emerges on Europa" (Science 276:355 April 18, 1997). McKinnon describes recent evidence for liquid water on Europa in "Planetary Explorations: Sighting the Seas of Europa" (Nature 386:765-7) and Zimmeran describes recent Galileo findings and NASA's possible Europa Ice Clipper Mission in "Moon Rivers" (The Sciences 37:11 March/April 1997).
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