Enceladus: The Best Hope Yet for Extraterrestrial Life

When the Cassini spacecraft (launched October 15,				from the sun) and shielding (parts of the moon’s
1997) flew within 175 km (109 miles) of Enceladus in				surface are shielded by Saturn because of its
July 2005, everything believed known about the				synchronous rotation) factors.
Saturnian moon had to be discarded. With the				Cryophiles
unexpected discovery of a huge water geyser and				Living and fossilized cryophilic (cold-loving) microbes
the heavy presence of water vapor in its atmosphere,				have been found in frigid Arctic environments where
a satellite previously believed to be small and				temperatures can drop as low as -90°Fahrenheit
“dead” (meaning no geological activity)				(Greenland and northern Siberia) to lower than
became the best hope to date for finding				-125°Fahrenheit (Antarctica). They have even
extraterrestrial life. Even though everything must be in				been found to exist at Sverrefjell Volcano located on
place to support the existence of life – water,				Svalbard, an island group north of Norway where
“an adequate heat source, proper chemical				“no living organisms would have been expected
nutrients, and precise environmental conditions [that]				[to exist, having] adapted to extremely cold
result in the necessary chemical				conditions.”[15]
reactions…”[1], Dr. Robert Brown, a planetary				Examples include a moss “that remained alive
scientist at the University of Arizona and a senior				yet dormant while frozen for 40,000 years in the
scientist working on the Cassini project “told a				permafrost of the Kolyma Lowlands of northeastern
major conference in Vienna, Austria [that] Enceladus				Siberia,”[16] orange mosses covered with black
contains… the ingredients for life.”[2]				films of cyanobacteria” have been found
History and Description:				growing “on the ice of the Matanuska Glaciar in
Enceladus, discovered on August 28, 1789 by German				Alaska” as well as actinomycetes
born British Astronomer Sir William Herschel				(“filamentous or
(1738-1822), best known for his discovery of Uranus, is				rod-shaped…microorganisms [that] resemble
the sixth largest moon of Saturn, with a mean				bacteria and fungi”) and other metabolically
diameter of 504 km (313 miles), approximately seven				diverse microbes found in ancient ice samples
times smaller than the Earth’s moon. It orbits				retrieved from Beacon Valley, Antarctica and other
Saturn “at a distance of 238,000 km (147,886				arctic locales.[17]
miles) from the planet’s center and 180,000 km				The recent discovery of “a new species of
(111,847 miles) from its surface, between the orbits of				polychaete worm (also known as pink “ice
Mimas and Tethys (two other Saturnian moons),				worms” that are about 1 to 2 inches in length)
rotating “synchronously… keeping one face				found living on the exposed surface of methane (CH4)
pointed towards Saturn” and completes each				gas hydrate mound[s]” in frigid waters deep
revolution in 32.9 hours.[3]				beneath the ocean surface are another positive
Based on findings from Cassini, Enceladus consists of				sign.[18] However, the greatest encouragement comes
a core with a higher percentage of irons (FE) and				from the discovery of chemosynthetic cryophiles that
silicates (compound consisting of Silicon (Si) and				require no energy source for metabolism. In lieu of
Oxygen (O), one or more metals, and possibly				such a source, these organisms obtain energy merely
hydrogen (H)) that may have undergone more heating				from “chemical reactions between rock and
from radioactive decay than the interiors of				water (H2O).”[19]
Saturn’s other mid-sized icy moons. Enceladus				Thermophiles
has a light gravitational field, yielding a density of 1.61				Living and fossilized microbes have been found in
grams per cubic centimeter.				geothermal or geologically active environments. One
Though known to exist for nearly two centuries,				example is the existence of chemosynthetic,
Enceladus, “one of only three outer solar system				thermophilic (heat-loving) microbes that exist in
bodies (along with Jupiter’s moon Io and				Yellowstone’s Norris Geyser Basin where
Neptune’s moon Triton) where active eruptions				temperatures consistently exceed 158°Fahrenheit
have been observed” remained a mere speck				and photosynthesis cannot occur. Accordingly they
until the Voyager program. When Voyager I flew by				use hydrogen (H2) to fuel their metabolism. This is
within 202,000 km (125,517 miles) of Enceladus on				especially encouraging since hydrogen (H) is a major
November 12, 1980, it revealed “a highly reflective				component of water (H2O) found in Enceladus’
surface devoid of impact craters, [indicative of] a				geysers and because the sunlight reaching
youthful surface.” Voyager II, which flew by				Enceladus’ surface is likely insufficient for
within 87,010 km (54,065 miles) of Enceladus on				photosynthesis.
August 26, 1981 revealed a diverse surface –				In addition, chemosynthetic, thermophilic or
some of it older and heavily cratered (mid-to-high				hyperthermophilic (extreme-heat-loving) microbes
northern latitude region), others lightly cratered (near				utilizing hydrogen sulfide (H2S) for metabolic functions
the equator) and the remainder generally smooth and				(e.g. bacterium Aquifex aeolicus) and prokaryotic
youthful.[4]				bacteria and cyanobacteria, along with larger
The February 17, March 9, and July 14, 2005 flybys of				organisms such as giant tube worms (Rifita pachyptila),
Cassini revealed Enceladus’ surface in				huge clams (Caliptogena), and mussels), have also
significantly greater detail. “Smooth plains				been found by the Earth’s deep water
resolved into relatively crater-free regions filled with				geothermal vents where temperatures can reach
numerous small ridges and scarps. …Numerous				716ºFahrenheit and sunlight cannot penetrate.
fractures (possibly caused by the build up of pressure				When it comes to bacterium Aquifex aeolicus, its
from the temperature differential between the				requirements are very simple. These heat-loving
moon’s warm subsurface and frigid surface and				microorganisms “need little more than hydrogen
exterior environment) were found within the older,				(H), oxygen (O), carbon dioxide (CO2) and mineral salts
cratered terrain… and several additional young				to grow” [20] improving the odds that similar or
terrain were discovered… such as… near the				like-kind chemosynthetic organisms may exist on
[moon’s] South Pole …[including] intriguing				Enceladus, especially in its geothermal pressure
dark spots, 125 and 750 meters (410 and 2461 feet)				chambers below the surface.
wide, which appear to run parallel to narrow fractures				Other Extremophiles
[and are believed to be] collapse pits” filled with				Along with thermophilic and cryophilic extremophiles
thick blue ice. Cassini also imaged the moon’s				(organisms that thrive in harsh “un-lifelike”
smooth plains (Sarandib Planitia and Diyar Planitia)				environments), a third form also exists –
leading to the estimate that this terrain is between 170				anaerobic life that thrives in non-oxygen environments
million to 3.7 billion years old, as well as the surface				beneath the Earth’s crust. Their existence
area facing Saturn, which was found to be				further improves the chances that extraterrestrial life
“covered in numerous criss-crossing sets of				may exist on Enceladus, especially since the most
troughs and ridges,” and the geologically active				likely habitat for such life may be below the Saturnian
South Pole, which revealed the presence of an active				moon’s surface.
geyser whose gushing water adds to Saturn’s				“Lunar” Microbes
e-ring, and a “distinctive tectonically-deformed				Perhaps the most fascinating example that points to
region [estimated to be between 10 to 100 million years				the possibility of life on Enceladus is the proven fact
old that reaches] as far north as 60° south				that exposed microbes can survive in the harshness
latitude… covered in tectonic fractures and ridges				of space. When the Surveyor 3 probe landed on the
[including four such fractures bounded on each side by				Moon (Earth’s moon) on April 20, 1967, it had
ridges called ‘tiger stripes’ covered in ice				been inadvertently populated by between 50 to 100
and even boulders ranging from 10 to 100 meters (33				microbes (Streptococcus mitis) that “survived
to 328 feet) wide, which appear to be less than 1000				launch, space vacuum, 3 years of radiation exposure,
years old].”[5]				deep-freeze at an average temperature of only
The discovery of the cryovolcanism (“eruption of				20º above absolute zero
water and/or other liquid or vapor-phase volatiles,				(-453ºFahrenheit), and no nutrient, water or
together with gas-driven solid fragments onto the				energy source.”[21] These organisms were still
surface of a planet or moon due to internal				alive when the contaminated camera of Surveyor 3
heating”)[6] at Enceladus’ South Pole, in				was retrieved and returned to Earth by the Apollo 12
which a geyser gushes water and other volatiles				crew on November 12, 1969.
instead of silicate rock, along with the presence of an				Conclusion:
inconstant atmosphere (thickest around the South				The prospects of finding extraterrestial life on
Pole) that consists mainly of water vapor (H2O)(91%)				Enceladus are exceptionally encouraging.
along with smaller amounts of molecular nitrogen (N)				“Enceladus… has the fundamental chemical
(4%), carbon dioxide (CO2)(3.2%) and methane (CH4)				recipe for life. Add a pinch of phosphorous and you
(1.7%) provides the greatest hope for the existence of				have all you need to make DNA – or perhaps
life somewhere on or beneath the moon’s				some other DNA-like molecule,” Robert Brown,
surface despite a mean surface temperature of about				declared.”[22]
-325° Fahrenheit.				Based on the existence of critical ingredients of life, the
Enceladus’ Water Geysers:				diverse adaptability and growing numbers of
When Cassini flew over Enceladus in November 2005,				discovered extremophiles thriving in places that appear
it confirmed the January 16, 2005 discovery of				uninhabitable and hostile to life, along with the amazing
numerous geyser-like jets of water and ice particles				survival of the Surveyor 3 microbes, Enceladus
(the composition was determined during the July 2005				appears to be the best hope yet of finding
flyby when Cassini flew directly through the plume),				extraterrestrial life. However additional exploration,
rising from multiple numbers of fractures or vents				analyses and research need to be conducted to
(“tiger stripes”) in the moon’s icy				confirm the existence of this life, the age-old quest of
crust. One of the plumes rose as high as 500 km (311				planetology, since in the words of Carl Sagan
miles), powered by pressurized sub-surface chambers,				(1934-1996), a legendary scientist, astronomer and
temperature differentials, the moon’s weak				author, “extraordinary claims require
gravity – about 12½ times weaker than the				extraordinary evidence.”[23]
Earth’s gravitational force, and to some degree				While Cassini will conduct flybys of Enceladus in 2006
the gravitational pull of Saturn.				and 2007, the greatest prospect for confirming the
Based on “the combined analysis of imaging,				existence of extraterrestrial life or moving closer in this
mass spectrometry, and magnetospheric data,” it				direction lies with the March 12, 2008 rendezvous. On
is likely that Enceladus’ plumes of water and ice				this day, Cassini will fly through the moon’s plume
particles emanate from “pressurized sub-surface				of water and ice particles, passing within 23 km (15
chambers [located less than 100 meters (328 feet)				miles) of Enceladus’ surface (if mission control
below the moon’s icy surface that consist of				deems it safe enough). However, the likely two-year
near pure water heated to about				extension of Cassini’s mission scheduled to end
26°-32°Fahrenheit prior to ejection], similar to				in 2008 and additional missions including landing probes
geysers on Earth.”[7] Further confirmation that				(especially at Enceladus’ south pole) will be
the water is liquid beneath the surface came from an				needed, since in the words of Carolyn Porco, a Cassini
analysis conducted by Cassini on the ice surrounding				imaging team leader at the Space Science Institute,
the “tiger stripe” fractures. “That ice				“It’s not clear that Cassini has the means
was amorphous and virtually crater-free, indicating that				to determine if the ice crystals themselves contain
it welled up relatively recently.”[8]				microbes. It may require a device with much greater
Furthermore, because of the absence of ammonia				compositional precision than we have, so that may
(NH3), which can serve as anti-freeze for water, it is				have to be left for a future mission [since] we will want
also likely that the moon’s sub-surface water is				to do a better job of determining the composition of
heated by tidal (frictional forces arising from flexure or				the ices comprising the fractures, which contain the
shifting caused by the gravitational pull of Saturn, 2:1				simplest organic compounds not found anywhere
“mean motion orbital resonance with				else.”[24]
Dione,”[9] a nearby moon, meaning that				_____________
Enceladus completes two orbits of Saturn for every				[1] Jeffrey Zweerink, Ph.D. Enceladus: Liquid Water But
one by Dione, and to a lesser degree the gravitational				No Life.
pull of Tethys, another nearby moon) or radiogenic				[2] Richard Black. Saturn’s moon ‘best bet
(caused by radioactivity or a radioactive				for life.’
transformation) sources, since Enceladus’ South				[3] Enceladus (moon).
Pole temperature is about -177°Fahrenheit versus				[4] Enceladus (moon).
the frigid -298° to -325°Fahrenheit for much				[5] Enceladus (moon).
of the rest of the moon’s surface and because				[6] David Darling. cryovolcanism.
the water and ice-particles must “have a certain				[7] Enceladus (moon).
density… that implies surprisingly warm				[8] Alan Boyle. Liquid water on Saturn moon could
temperatures” to be carried aloft.[10] The				support life.
difference is too great to be explained by solar heating				[9] Enceladus (moon).
since Enceladus’ icy surface reflects more 90%				[10] Enceladus Erupting. Astrobiology Magazine.
of the sun’s weak energy back into space.				[11] Bill Arnett. Enceladus. Saturn II.
Accordingly the moon “has the highest albedo				[12] Hydrothermal Environments on the Ocean Floor.
(ratio of reflected to incident light) of any body in the				and
solar system” with a measurement of >0.9.[11]				[13] Peter N. Spotts. Life beyond Earth? Potential
According to research presented at a European				habitats in the solar system keep popping up.
Geosciences Union (EGU) conference in April 2006,				[14] Michael Schirber. How Life Began: New Research
Enceladus’ core of molten rock may be as hot				Suggests Simple Approach.
as 2060°Fahrenheit further bolstering the theory				[15] David L. Chandler. Mars-bound instruments detect
that the moon’s geological activity is fueled by				Arctic microbes.
tidal and radiogenic sources.				[16] Search for life on Mars will start in Siberia.
Likely Life Forms on Enceladus				[17] Astrobiologists To Hunt Small Game in Siberia. and
If life is to be found on Enceladus, it is likely to be in the				[18] Cold Methane Environments on the Ocean Floor.
form of extremely simple microbes that can exist in				[19] Life in Extreme Environments.
harsh, seemingly uninhabitable environments as long as				[20] Hydrothermal Environments on the Ocean Floor.
chemical nutrients, biomolecules such as amino acids,				[21] On Earth: Extreme Environments.
an energy source and liquid water are present, which				[22] Peter N. Spotts. Life beyond Earth? Potential
appears to be the case in when it comes to the				habitats in the solar system keep popping up.
pressurized chambers that provide geothermal				[23] Alan Boyle. Liquid water on Saturn moon could
warming to the moon.				support life.
The Case for Possible Extraterrestrial Life:				[24] Leonard David. Saturnian moon inspires a gusher
Ingredients For Life:				of questions.
Two important ingredients for life are water (H2O) and				_____________
an energy source (though it has been found to be				Sources:
unnecessary for some chemosynthetic cryophiles) to				Alan Boyle. Liquid water on Saturn moon could support
fuel and sustain an organism’s metabolism. Both				life. 9 March 2006.
are present on Eceladus. Resevoirs of liquid water run				Alfred S. McEwen. Cassini Unveils Saturn. Astronomy.
beneath the moon’s surface while about 99.9%				July 2006 (Kalmbach Publishing Co., Waukesha, WI.,
of its topography is covered in water (H2O) ice that is				USA).
constantly refreshed by the shooting geysers that rain				Astrobiologists To Hunt Small Game in Siberia.
down as ice particles and snow. At the same time, the				Science@NASA. 27 July 1999. 13 June 2006.
hydrothermal jets that power Enceladus’				Astrobiology Research Program – (ii) Origins of
geysers provide an optimal habitat for microorganisms				Life. Origins Institute at McMaster University. Hamilton,
in the same way the deep-water and Yellowstone				Ontario, Canada. 2006. 13 June 2006.
National Park’s hydrothermal vents do on Earth.				Bill Arnett. Enceladus. Saturn II. 17 February 2005. 13
A third ingredient is Nitrogen, which is present on				June 2006.
Enceladus and in its atmosphere. “Nitrogen is an				Calvin J. Hamilton. Enceladus. Saturn II. 2005. 13 June
essential ingredient of amino acids (“organic				2006.
compounds containing an amino group (NH2), a				Cold Methane Environments on the Ocean Floor. 13
carboxylic acid group (COOH), and any of various side				June 2006. [
groups, especially any of the 20 compounds that have				Craig Levin. Life on Ice: The Possibility of Life on
the basic formula NH2CHRCOOH, and that link				Europa and Enceladus. 1990. 13 June 2006. [
together by peptide bonds to form proteins or that				David L. Chandler. Mars-bound instruments detect
function as chemical messengers and as intermediates				Arctic microbes. 5 October 2005. 13 June 2006.
in metabolism”), commonly referred to as the				David Darling. cryovolcanism. The Encyclopedia of
building blocks of life) and nucleic acids (“complex				Astrobiology and Spaceflight. 16 June 2006.
compounds found in all living cells and viruses,				Lexico Publishing Group, LLC. 2006. 15 June 2006.
composed of purines, pyrimidines, carbohydrates, and				Earth microbes on the moon. Science@NASA. 1
phosphoric acid. Nucleic acids in the form of DNA and				September 1998. 15 June 2006.
RNA control cellular function and heredity”).[12]				Elizabeth Svoboda. Saturn Moon Has Water Geysers
A fourth ingredient is the presence of organic				and, Just Maybe, Life. National Geographic News. 10
compounds, substances consisting of carbon (C), the				March 2006. 13 June 2006.
signature element of life. Based on Cassini’s				Enceladus Erupting. Astrobiology Magazine. 7
flybys, the existence of simple organic compounds				December 2005. 13 June 2006.
have been detected along the “tiger stripe”				Enceladus (moon). 2006. 13 June 2006.
fractures and in the plumes of water and ice crystals				Exploring the deep ocean floor: Hot springs and
gushing from the moon’s geysers. Small				strange creatures. USGS. 13 June 2006.
amounts of methane (CH4), carbon dioxide (CO2) and				Henry Bortman. Some Like It Hot. 7 March 2001. 13
propane (C3H8) have been detected in the plumes				June 2006.
while small amounts of carbon dioxide (CO2) and				Hydrothermal Environments on the Ocean Floor. 13
methane (CH4) have been found in Enceladus’				June 2006. [
atmosphere. In addition, Cassini also detected the				J. Parnell, et al. Simple Devices For Concentration of
presence of ethane (C2H6) and ethylene (C2H4) two				Microbial Life… 13 June 2006. [
additional organic compounds.				Jeffrey Zweerink, Ph.D. Enceladus: Liquid Water But
A fifth ingredient is the existence of some kind of				No Life. 2005. 13 June 2006. [
“basis for complex chemistry.”[13] When				Jonathan Amos. Saturn moon delights and baffles. 30
viewing scientific theories about the beginning of life on				August 2005. 13 June 2006.
Earth, such a chemistry is not unattainable for bodies				Leonard David. Saturnian moon inspires a gusher of
elsewhere in the space. In both the “primordial				questions. 3 April 2006. 13 June 2006.
soup” (in which biological compounds such as				Life in Extreme Environments. 2005. 13 June 2006.
amino acids emerged from an “organic				Mark L. Skidmore et al. Microbial Life beneath a High
broth”) and “metabolism first” (in				Arctic Glacier. American Society for Microbiology.
which life emerged from small molecules, even tinier				August 2000. 13 June 2006.
than RNA, recently bolstered by the discovery of				Michael Schirber. How Life Began: New Research
Methanosarcina acetivorans, an undersea microbe,				Suggests Simple Approach. Live Science. 9 June 2006.
“which eats carbon monoxide (CO) and expels				13 June 2006.
methane (CH4) and acetate (CH3COO)”[14]				Microbes in Colorful Yellowstone Hot Springs Fueled
using only “two very simple proteins” for				By Hydrogen, CU-Boulder Researchers Say. University
chemosynthesis to sustain its metabolism) theories, the				of Colorado at Boulder. Boulder, CO. 24 January 2005.
prerequisites for the beginning of life on Earth were not				13 June 2006.
insurmountably great, especially since this life originally				On Earth: Extreme Environments. 13 June 2006. [
arose under harsh conditions when the Earth’s				Peter N. Spotts. Life beyond Earth? Potential habitats in
atmosphere consisted primarily of toxic substances				the solar system keep popping up. The Christian
such as ammonia (NH3), carbon dioxide (CO2),				Science Monitor. 29 September 2005. 13 June 2006.
methane (CH4), and steam.				Richard Black. Saturn’s moon ‘best bet for
The prospects for life may also be enhanced because				life.’ BBC 10 April 2006. 13 June 2006. [
Enceladus does not have an intense radiation field and				Search for life on Mars will start in Siberia.
because of the reduced potency of the sun’s				Science@NASA. 27 May 1999. 13 June 2006.
harmful ultraviolet (UV) rays due to time (longer to				Tiny Enceladus May Hold Ingredients of Life. 5
reach), distance (1.427 billion km or 886 million miles				September 2005. 13 June 2006.

Dophins

Enceladus: The Best Hope Yet for Extraterrestrial Life