Europa Archives

November 11, 2010December 24, 2015 by Nancy Atkinson

Europa’s Tidal Processes Give Hints to Our Moon’s Far-side Bulge

The Moon's crust is thickest on the central farside, and becomes thinner towards the north pole in a manner described by a simple mathematical function. Early in lunar evolution, when a magma ocean was present, tides from the Earth could have heated the floating crust nonuniformly, such that the crust thinned at the poles and thickened at the equator. Today, the magma ocean has solidified, but the thick farside crust remains. Figure not to scale. Image © Science/AAAS

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A self-conscious Moon might ask, “Does my far side look big?” To which lunar scientists would have to reply in the affirmative. They have long known there is a bulge on the Moon’s far side, a thick region of the lunar crust which underlies the farside highlands. But why that bulge is there has been a mystery, and the fact that the far side always faces away from Earth hasn’t helped. Now, a group of international scientists have found that perhaps the tidal processes of Jupiter’s icy moon, Europa, can provide a clue.

“Europa is a completely different satellite from our moon, but it gave us the idea to look at the process of tidal flexing of the crust over a liquid ocean,” said Ian Garrick-Bethell, the lead author of a new paper that offers an explanation for the lop-sided Moon.

Since the Apollo 15 laser altimeter experiment, scientists have known that a region of the lunar far side highlands is the highest place on the Moon. Additionally, the far side has only highlands and no maria.

Like Europa’s icy crust that sits over an ocean of liquid water, the Moon’s crust once floated on a sub-surface ocean of liquid rock. So, could the same gravitational forces from Jupiter that influence Europa also apply to the Earth’s influence on the early Moon?

Garrick-Bethell, from UC Santa Cruz, and his team found that the shape of the Moon’s bulge can be calculated by looking at the variations in tidal heating as the ancient lunar crust was being torn away from the underlying ocean of liquid magma.

Map of crustal thickness. Credit: Garrick-Bethell, et al.

With Europa in mind, the scientists looked at global topography and gravity data sets of the Moon, trying to determine the possibility of how about 4.4 billion years ago, the gravitational pull of the Earth could have caused tidal flexing and heating of the lunar crust. At the polar regions, where the flexing and heating was greatest, the crust became thinner, while the thickest crust would have formed in the regions in line with the Earth.

To back up their theory, they found that a simple mathematical function — a 2-degree spherical harmonics function — can explain the phenomenon. “What’s interesting is that the form of the mathematical function implies that tides had something to do with the formation of that terrain,” said Garrick-Bethell.

The far side of the Moon, photographed by the crew of Apollo 11 as they circled the Moon in 1969. The large impact basin is Crater 308. Credit: NASA

However, this doesn’t explain why the bulge is now found only on the farside of the Moon. “You would expect to see a bulge on both sides, because tides have a symmetrical effect,” Garrick-Bethell said. “It may be that volcanic activity or other geological processes over the past 4.4 billion years have changed the expression of the bulge on the nearside.”

Garrick-Bethell said his team hopes to continue to do more modeling and calculations to fully describe the far side’s features.

“It’s still not completely clear yet, but we’re starting to chip away at the problem,”he said.

The paper will be published in the November 12, 2010 issue of Science.

(Paper not yet available — we’ll post the link when it goes online).

October 4, 2010July 20, 2018 by Nancy Atkinson

Acid Rain-Like Chemistry Could Occur in Europa’s Ice Crust

Europa, a moon of Jupiter, appears as a thick crescent in this enhanced-color image from NASA's Galileo spacecraft. Credit: NASA

A new look at how chemicals on Jupiter’s moon Europa may be reacting together could provide new insight to how chemical reactions could be occurring in the moon’s icy crust, despite frigid temperatures. Researchers have found that water and sulfur dioxide react together very quickly, even at temperatures hundreds of degrees below freezing. Because the reaction occurs without the aid of radiation, it could take place throughout Europa’s thick coating of ice. If this is occurring, it would revamp current thinking about the chemistry and geology of this moon and perhaps others.

Europa has temperatures around 86 to 130 Kelvin (minus 300 to minus 225 degrees Fahrenheit), and in those extremely cold conditions, most chemical reactions require an infusion of energy from radiation or light. On Europa, the energy comes from particles from Jupiter’s radiation belts. Because most of those particles penetrate just fractions of an inch into the surface, models of Europa’s chemistry typically stop there.

“When people talk about chemistry on Europa, they typically talk about reactions that are driven by radiation,” says Goddard scientist Reggie Hudson. “Once you get below Europa’s surface, it’s cold and solid, and you normally don’t expect things to happen very fast under those conditions,” said Reggie Hudson, from NASA Goddard’s Astrochemistry Laboratory.

“But with the chemistry we describe,” said Mark Loeffler, who is first author on the paper being published in Geophysical Research Letters, “you could have ice 10 or 100 meters [roughly 33 or 330 feet] thick, and if it has sulfur dioxide mixed in, you’re going to have a reaction.”

Spectroscopy shows there is sulfur in Europa’s ice, and astronomers believe it originates from the volcanoes of Jupiter’s moon Io, then becomes ionized and is transported to Europa, where it gets embedded in the ice. But originally, astronomers thought not much of a reaction could occur between water ice and the sulfur.

Loeffler and Hudson sprayed water vapor and sulfur dioxide gas onto quarter-sized mirrors in a high-vacuum chamber. Because the mirrors were kept at about 50 to 100 Kelvin (about minus 370 to minus 280 degrees Fahrenheit), the gases immediately condensed as ice. As the reaction proceeded, the researchers used infrared spectroscopy to watch the decrease in concentrations of water and sulfur dioxide and the increase in concentrations of positive and negative ions generated.

Even with the extremely cold temperatures, the molecules reacted quickly in their icy forms. “At 130 Kelvin [about minus 225 degrees Fahrenheit], which represents the warm end of the expected temperatures on Europa, this reaction is essentially instantaneous,” said Loeffler. “At 100 Kelvin, you can saturate the reaction after half a day to a day. If that doesn’t sound fast, remember that on geologic timescales-billions of years-a day is faster than the blink of an eye.”

To test the reaction, the researchers added frozen carbon dioxide, also known as dry ice, which is commonly found on icy bodies, including Europa. “If frozen carbon dioxide had blocked the reaction, we wouldn’t be nearly as interested,” said Hudson, “because then the reaction probably wouldn’t be relevant to Europa’s chemistry. It would be a laboratory curiosity.” But the reaction continued, which means it could be significant on Europa as well as Ganymede and Callisto, two more of Jupiter’s moons, and other places where both water and sulfur dioxide are present.

The reaction converted one-quarter to nearly one-third of the sulfur dioxide into different products. “This is an unexpectedly high yield for this chemical reaction,” said Loeffler. “We would have been happy with five percent.”

What’s more, the positive and negative ions produced will react with other molecules. This could lead to some intriguing chemistry, especially because bisulfite, a type of sulfur ion, and some other products of this reaction are refractory-stable enough to last for quite some time.

This new finding will certainly prompt new remote observations of Europa to see whether evidence of any reaction-based products can be found.

Source: JPL

July 22, 2010December 24, 2015 by Ryan Anderson

Europa Analog Deep-Sea Vents Discovered in the Caribbean

A team recovers the hybrid robotic vehicle Nereus aboard the research vessel Cape Hatteras during a partially NASA-funded expedition to the Mid-Cayman Rise in October 2009. A search for new hydrothermal vent sites along the 110-kilometer-long ridge, the expedition featured the first use of Nereus in "autonomous," or free-swimming, mode. Image credit: Woods Hole Oceanographic Institution

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White sand, blue water, sunny skies, pina coladas. When you think of “extreme environments” I doubt the Caribbean is high on your list. But a team of scientists from Woods Hole Oceanographic institute and NASA’s Jet Propulsion Laboratory, exploring the 68-mile-long Mid-Cayman rise deep beneath the surface of the Caribbean, have discovered the deepest known hydrothermal vent in the world, along with two other distinct types of vents.

The mid-Cayman rise is a much smaller version of the mid-ocean ridge system, a chain of submarine mountains that encircles the globe. These ridges form in locations where tectonic plates are pulling apart, allowing mantle rocks to melt and emerge at the surface as lava. Seawater, percolating through the hot rocks at these spreading centers, is superheated and emerges at vents, bearing a rich bounty of dissolved nutrients to support thriving ecosystems that can live without any sunlight.

“This was probably the highest-risk expedition I have ever undertaken,” said chief scientist Chris German, a Woods Hole Oceanographic Institution geochemist who has pioneered the use of autonomous underwater vehicles to search for hydrothermal vent sites. “We know hydrothermal vents appear along ridges approximately every 100 kilometers [62 miles]. But this ridge crest is only 100 kilometers long, so we should only have expected to find evidence for one site at most. So finding evidence for three sites was quite unexpected – but then finding out that our data indicated that each site represents a different style of venting – one of every kind known, all in pretty much the same place – was extraordinarily cool.”

In addition to the deepest hydrothermal vent yet discovered, at a depth of 5,000 meters (16,400 feet), the team also found a shallower low-temperature vent. Only one other vent of this type has been discovered: the famous “Lost City” vent in the Atlantic.

“We were particularly excited to find compelling evidence for high-temperature venting at almost 5,000 meters depth,” said Julie Huber, a scientist in the Josephine Bay Paul Center at the Marine Biological Laboratory in Woods Hole. “We have absolutely zero microbial data from high-temperature vents at this depth.”

The ecosystems encrusting the deep sea vents on the mid-Cayman rise provide valuable clues to how life could arise and thrive elsewhere in the solar system. “Most life on Earth is sustained by food chains that begin with sunlight as their energy source. That’s not an option for possible life deep in the ocean of Jupiter’s icy moon Europa,” said JPL co-author Max Coleman.

With an airless sky, intense radiation, icy crust, and no pina coladas, the surface of Europa is about as different from the Caribbean as you can get. But deep on the sea floor, they may be remarkably similar.

“Organisms around the deep vents get energy from the chemicals in hydrothermal fluid, a scenario we think is similar to the seafloor of Europa,” Coleman said. “This work will help us understand what we might find when we search for life there.”

An artist's depiction of a future Europa mission. Image credit: NASA

October 8, 2009July 20, 2018 by Nancy Atkinson

Europa Capable of Supporting Life, Scientist Says

Europa. CThe cracked, icy surface of Europa. The smoothness of the surface has led many scientists to conclude that oceans exist beneath it. Credit: NASA/JPLredit: NASA

The global ocean on Jupiter’s moon Europa contains about twice the liquid water of all the Earth’s oceans combined. New research by Richard Greenberg of the University of Arizona suggests that there may be plenty of oxygen available in that ocean to support life, a hundred times more oxygen than previously estimated.

The chances for life there have been uncertain, because Europa’s ocean lies beneath several miles of ice, which separates it from the production of oxygen at the surface by energetic charged particles (similar to cosmic rays). Without oxygen, life could conceivably exist at hot springs in the ocean floor using exotic metabolic chemistries, based on sulfur or the production of methane. However, it is not certain whether the ocean floor actually would provide the conditions for such life.

Therefore a key question has been whether enough oxygen reaches the ocean to support the oxygen-based metabolic process that is most familiar to us. An answer comes from considering the young age of Europa’s surface. Its geology and the paucity of impact craters suggests that the top of the ice is continually reformed such that the current surface is only about 50 million years old, roughly 1% of the age of the solar system.

Greenberg has considered three generic resurfacing processes: gradually laying fresh material on the surface; opening cracks which fill with fresh ice from below; and disrupting patches of surface in place and replacing them with fresh material. Using estimates for the production of oxidizers at the surface, he finds that the delivery rate into the ocean is so fast that the oxygen concentration could exceed that of the Earth’s oceans in only a few million years.

Greenberg says that the concentrations of oxygen would be great enough to support not only microorganisms, but also “macrofauna”, that is, more complex animal-like organisms which have greater oxygen demands. The continual supply of oxygen could support roughly 3 billion kilograms of macrofauna, assuming similar oxygen demands to terrestrial fish.

The good news for the question of the origin of life is that there would be a delay of a couple of billion years before the first surface oxygen reached the ocean. Without that delay, the first pre-biotic chemistry and the first primitive organic structures would be disrupted by oxidation. Oxidation is a hazard unless organisms have evolved protection from its damaging effects. A similar delay in the production of oxygen on Earth was probably essential for allowing life to get started here.

Richard Greenberg is the author of the recent book “Unmasking Europa: The Search for Life on Jupiter’s Ocean Moon.” He presented his findings at the 41st meeting of the American Astronomical Society’s Division for Planetary Sciences.

Source: AAS DPS

November 12, 2008April 26, 2016 by Nancy Atkinson

Europa Submarine Prototype Gets Another Test

ENDURANCE submarine. Credit: John Rummel, NASA

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A submersible probe that could possibly be used on Jupiter’s icy moon, Europa is taking the next step to test its capabilities. The Environmentally Non-Disturbing Under-ice Robotic Antarctic Explorer, also known as ENDURANCE, will swim untethered under ice, and collect data to create three-dimensional maps of underwater environments. The probe also will take samples of microbial life. Earlier this year, it operated successfully in a 25 meter frozen lake in Wisconsin, USA. Now it will plunge under a permanently ice covered lake in Antarctica that is 40 meters deep. ENDURANCE isn’t like the Mars Rovers or other remote-operated probes. Once deployed, it’s on its own to systematically explore, take water samples, and find its way back. “It will have to think on its own,” said Peter Doran, an Earth scientist at the University of Illinois in Chicago.

In the February 2008 test, ENDURANCE successfully found its way around the bottom of the lake and back to the hole that drilled in the ice to get the probe in and out of the lake. It also demonstrated that its electronics functioned perfectly well in cold water.

At Lake Bonney in Antarctica, ENDURANCE will not only map the lake and explore its biology, but also take a close look at the base of a feature called Blood Falls, where reddish, iron-containing salts spill out of the face of a glacier at the lake’s upper end.

If all goes well the next test would have the probe or an improved version descend through 3.5 km of ice to one of the world’s largest, deepest and most mysterious lakes, Lake Vostok, also in Antarctica.
But even that pales in comparison to what a probe might encounter at Europa. Scientists believe that Europa’s ocean could be up to 100 kilometers deep, under 6 kilometers of ice.

Hot water drills will bore a hole for ENDURANCE to enter the water in Antarctica. If all goes well, the probe will be tested again in 2009.

But many hurdles remain before an underwater vehicle could possibly head to Europa. Presently, Endurance is too massive to send on interplanetary travel. Engineers will also have to come up with a way to drill through Europa’s icy crust and lower the sub safely through the ice.

But many scientists feel that an orbiting spacecraft would be the best way to study Europa, before sending an underwater probe. The Jet Propulsion Laboratory is currently working on a concept called the Europa Explorer which would deliver a low orbit spacecraft to determine the presence (or absence) of a liquid water ocean under Europa’s ice surface. It would also map the surface and subsurface for future exploration.

Source: COSMOS

May 14, 2008December 24, 2015 by Nancy Atkinson

Pole Shift on Europa?

Curved features on Jupiter’s moon Europa may indicate that its poles have wandered by almost 90°, a new study reports. Researchers believe the drastic shift in Europa’s rotational axis was likely a result of the build-up of thick ice at the poles. â€œA spinning body is most stable with its mass farthest from its spin axis,” says Isamu Matsuyama of the Carnegie Institution’s Department of Terrestrial Magnetism. “On Europa, variations in the thickness of its outer shell caused a mass imbalance, so the rotation axis reoriented to a new stable state” An extreme shift like this also suggests the existence of an internal liquid ocean beneath the icy crust.

The research team, led by Dr. Paul Schenk of the Lunar and Planetary Institute and joined by Matsuyama and Dr. Francis Nimmo of the University of California, Santa Cruz, used images from the Voyager, Galileo, and New Horizons spacecraft to map several large arc-shaped depressions that extend more than 500 kilometers across Europaâ€™s surface. With a radius of about 1500 kilometers, Europa is slightly smaller than the Earthâ€™s moon.

By comparing the pattern of the depressions with fractures that would result from stresses caused by a shift in Europa’s rotational axis, the researchers determined that the axis had shifted by approximately 80°. The previous axis of rotation is now located about 10° from the present equator.

Such a change is called “true polar wander” as opposed to apparent polar wander caused by plate tectonics. There is evidence for true polar wander on Earth, and also on Mars and on Saturn’s moon Enceladus. “Our study adds Europa to this list,” says Matsuyama. “It suggests that planetary bodies might be more prone to reorientation than we thought.”

The study also has implications for liquid water inside Europa. Many scientists believe Europa has an extensive subsurface ocean based on spacecraft photos showing a fractured, icy surface. The ocean beneath the crust would be kept liquid by heat generated by tidal forces from Jupiter’s gravity. The presence of heat and water may make life possible, even though the subsurface ocean is cut off from solar energy.

“The large reorientation on Europa required to explain the circular depressions implies that its outer ice shell is decoupled from the core by a liquid layer,” says Matsuyama. “Therefore, our study provides an independent test for the presence of an interior liquid layer.”

Original News Source: EurekAlert

February 9, 2008December 26, 2015 by Nancy Atkinson

Testing a Europa Probe Prototype

While NASA doesn’t have any definite plans to send a probe to study Jupiter’s moon Europa, many planetary scientists consider the exploration of this enticing moon to be a high priority. Evidence from the Voyager and Galileo spacecraft suggests Europa contains a deep ocean of salty water under an icy outer shell. NASA is, however, helping to fund a prototype of an underwater autonomous vehicle to investigate ice covered lakes here on Earth, to demonstrate if such a vehicle could operate in an environment similar to Europa. The next test of the vehicle will take place Feb. 12-15, 2008 in Lake Mendota on the campus of the University of Wisconsin, Madison.

The Environmentally Non-Disturbing Under-ice Robotic Antarctic Explorer, also known as Endurance, will swim untethered under ice, and collect data to create three-dimensional maps of underwater environments. The probe also will look at the conditions in those environments and take samples of microbial life. Later this year, researchers plan to ship the probe to a permanently frozen lake in Antarctica for more operations. The probe is a follow-up to the Deep Phreatic Thermal Explorer, a NASA-funded project that completed a series of underwater field tests in Mexico in 2007.

“We’re using extreme environments on Earth as our laboratory,” says Peter Doran, associate professor at the University of Illinois at Chicago. “Ice-covered lakes are good, small-scale analogs to what we might find on Europa.”

Mendota Lake is only 25 meters deep, while the lake in Antarctica, West Lake Bonney is 40 meters deep. Scientists believe that Europa’s ocean could be up to 100 kilometers deep.

Hot water drills will bore a hole for Endurance to enter the water. If all goes well, the probe will be tested again in 2009.

But many hurdles remain before an underwater vehicle could possibly head to Europa. Presently, Endurance is too massive to send on interplanetary travel. Scientists will also have to come up with a way to drill through Europa’s icy crust and lower the sub safely through the ice.

And before a probe would be sent to land on Europa, many scientists feel that an orbiting spacecraft would be the best way to study the moon. The Jet Propulsion Laboratory is currently working on a concept called the Europa Explorer which would deliver a low orbit spacecraft to determine the presence (or absence) of a liquid water ocean under Europa’s ice surface. It would also map the surface and subsurface for future exploration.

Original News Sources: NASA Press Release, Washington University Press Release

December 14, 2007December 26, 2015 by Fraser Cain

Making the Case for Europa

Nick had an article last week about a new technique that might help scientists figure out just how deep the oceans on Europa are. Deep oceans with a thin crust might give a rover, or a submarine, a fighting chance to get down to that precious H2O, and sample it for evidence of life. Researchers are seriously discussing the benefits of exploring Europa at the annual meeting of the American Geophysical Union in San Francisco.

According to William McKinnon, a professor of Earth and Planetary Sciences at Washington University in St. Louis, Mo, “Weâ€™ve learned a lot about Europa in the past few years.

“Before we were almost sure that there was an ocean, but now the scientific community has come to a consensus that there most certainly is an ocean. Weâ€™re ready to take the next step and explore that ocean and the ice shell that overlays it. We have a number of new discoveries and techniques that can help us do that.”

What advances have been made?

There’s the research we talked about; how detailed observations of the Moon’s flexing under Jupiter’s intense gravity, as well as the magnetic variations can tell just how deep the ocean goes.

And new radar sounding techniques have been developed for other spacecraft that would be very useful at Europa. The high-resolution radar system installed on the Mars Reconnaissance Orbiter would be able to peer right through an ice shell on Europa, and give researchers a cross section of the ice. It would be able to locate liquid water under and within the shell, and put the controversy to rest forever.

Engineers are also working on future explorers, such as a project called Endurance, developed by Peter Doran, associate professor of Earth and Environmental Sciences, University of Illinois at Chicago and Stone Aerospace. They’ll be testing an exploration vehicle in Wisconsin in February 2008, and then in Antarctica.

This robotic explorer will be able to create three-dimensional maps of the subsurface lakes in Antarctica and even map out the biochemistry in the water. If there’s life there, Endurance will find it.

Obviously, sending a probe like this to Europa is a long, long way off. But people are chipping away at the problem on both ends. Scientists are making the case that Europa is one of the most enticing scientific targets in the Solar System. And engineers are working out the technologies that could actually make the discoveries.

The future for exploration on Europa is looking brighter every day.

Original Source: University of Texas at Austin News Release

December 4, 2007December 26, 2015 by Nicholos Wethington

Europa’s Ocean: Thick or Thin?

How do you determine the thickness of an ocean that you can’t see, let alone know how salty it is? Europa, the sixth satellite from Jupiter, is thought to have an ocean of liquid water underneath its icy surface. We know this because of its remarkably uncratered surface and the way its magnetic field reacts with that of Jupiter. New results that take into consideration Europa’s interaction with the plasma surrounding Jupiter â€“ in addition to the magnetic field â€“ give us a better picture of the ocean’s thickness and composition. This will help future robotic explorers know how deep they need to tunnel to reach the oceans underneath.

“We know from gravity measurements made by Galileo that Europa is a differentiated body. The most plausible models of Europa’s interior have an H2O-ice layer of thickness 80-170km. However, the gravity measurements tell us nothing about the state of this layer (solid or liquid),” said Dr. Nico Schilling of the Institut fÃ¼r Geophysik und Meteorologie in KÃ¶ln, Germany.

The water in Europa’s ocean â€“ just like the water in our own ocean â€“ is a good conductor of electricity. When a conductor passes through a magnetic field, electricity is produced, and this electricity has an effect on the magnetic field itself. It’s just like what happens inside an electric generator. This process is called electromagnetic induction, and the intensity of the induction gives a lot of information about the materials involved in the process.

But Europa doesn’t only interact with the magnetic field coming from Jupiter, however; it also has electromagnetic interactions with the plasma surrounding Jupiter, called the magnetospheric plasma. This same thing happens on Earth in a way that is very familiar: Earth has a magnetosphere, and when plasma coming from the Sun interacts with our magnetosphere we see the beautiful Aurora Borealis phenomenon.

This process, happening intermittently as Europa orbits Jupiter, has an effect on the induction field of the subsurface ocean of the moon. By combining these measurements with the previous measurements of the interaction between Europa and Jupiter’s magnetic field, the researchers were able to get a better picture of just how thick and how conductive Europa’s ocean is. Their results were published in a paper titled, Time-varying interaction of Europa with the jovian magnetosphere: Constraints on the conductivity of Europa’s subsurface ocean, which appears in the August 2007 edition of the journal Icarus.

The researchers compared their models of Europa’s electromagnetic induction with the results of Galileo’s magnetic field measurements, and found that the total conductivity of the ocean was about 50,000 Siemens (a measure of electrical conductivity). This is much higher than previous results, which placed the conductivity at 15000 Siemens.

Depending on the composition of the ocean, though, the thickness could be between 25 and 100km, which is also thicker than the previously estimated lower limit of 5km. The less conductive the ocean is, the thicker it must be to account for the measured conductivity, and this depends on the quantity and type of salt found in the ocean, which still remains unknown.

Taking into account the interactions with the magnetospheric plasma are important when studying the composition of planets and moons.

Dr. Schilling said, “The plasma interaction effects the magnetic field measurements, but not e.g. the gravity measurements. So in every case in the Jupiter system, where magnetic field measurements were used to get some informations from the interiors of the moons, the plasma interaction has to be considered. An example is for instance Io, where the first flybys suggested that Io may have an internal dynamo field. It turned out that the measured magnetic field perturbation was not an internal field but was created by the plasma interaction.”

Europa and Io, though, are not the only place where magnetic fields and plasma interactions can tell us about the nature of a planet’s interior; this same method was also used to detect the geysers of Enceladus, one of Saturn’s moons.

“The first hints of an active south polar region came from the magnetic field measurements and the simulations of the plasma interaction, before Cassini actually saw the geysers,” Dr. Schilling said.

With the discovery of entire ecosystems at the bottom of oceans here on Earth – ecosystems entirely cut off from sunlight – the discovery of oceans on Europa gives scientists hope that there could be life there. And this new discovery helps researchers understand what kind of ocean they could be dealing with.

Now, we just have to tunnel down through the shell of ice and look for ourselves.

Source: Icarus

August 29, 2007December 26, 2015 by Nancy Atkinson

A Submarine for Europa

Many planetary scientists believe that Jupiter’s moon Europa is our solar system’s best contender to share Earth’s distinction of harboring life. Evidence gathered by the Voyager and Galileo spacecrafts suggests Europa contains a deep, possibly warm ocean of salty water under an outer shell of fissured ice. In a paper published in the July 2007 Journal of Aerospace Engineering a British mechanical engineer proposes sending a submarine to explore Europa’s oceans.

Carl T. F. Ross, a professor at the University of Portsmouth in England offers an abstract design of an underwater craft built of a metal matrix composite. He also provides suggestions for suitable power supplies, communication techniques and propulsion systems for such a vessel in his paper, “Conceptual Design of a Submarine to Explore Europa’s Oceans.”

Ross’s paper weighs the options for constructing a submarine capable of withstanding the undoubtedly high pressure within Europa’s deep oceans. Scientists believe that this moon’s oceans could be up to 100 kilometers deep, more than ten times deeper than Earth’s oceans. Ross proposes a 3 meter long cylindrical sub with an internal diameter of 1 meter. He believes that steel or titanium, while strong enough to withstand the hydrostatic pressure, would be unsuitable as the vessel would have no reserve buoyancy. Therefore, the sub would sink like a rock to the bottom of the ocean. A metal matrix or ceramic composite would offer the best combination of strength and buoyancy.

Ross favors a fuel cell for power, which will be needed for propulsion, communications and scientific equipment, but notes that technological advances in the ensuing years may provide better sources for power.

Ross concedes that a submarine mission to Europa won’t occur for at least 15-20 years. Planetary scientist William B. McKinnon agrees.

“It is difficult enough, and expensive, to get back to Europa with an orbiter, much less imagine a landing or an ocean entry,” said McKinnon, professor of Earth and Planetary Sciences at Washington University in St. Louis, Missouri. “Sometime in the future, and after we have determined the ice shell thickness, we can begin to seriously address the engineering challenges. For now, it might be best to search for those places where the ocean has come to us. That is, sites of recent eruptions on Europa’s surface, whose compositions can be determined from orbit.”

The Jet Propulsion Laboratory is currently working on a concept called the Europa Explorer which would deliver a low orbit spacecraft to determine the presence (or absence) of a liquid water ocean under Europa’s ice surface. It would also map the distribution of compounds of interest for pre-biotic chemistry, and characterize the surface and subsurface for future exploration. “This type of mission,” says McKinnon, “would really allow us to get the hard proof we would all like that the ocean is really there, and determine the thickness of the ice shell and find thin spots if they exist.”

McKinnon added that an orbiter could find “hot spots” that indicate recent geological or even volcanic activity and obtain high-resolution images of the surface. The latter would be needed to plan any successful landing.

Slightly smaller than Earth’s moon, Europa has an exterior that is nearly craterless, meaning a relatively “young” surface. Data from the Galileo spacecraft shows evidence of near-surface melting and movements of large blocks of icy crust, similar to ice bergs or ice rafts on Earth.

While Europa’s midday surface temperatures hover around 130 K (-142 C, -225 degrees F), interior temperatures could be warm enough for liquid water to exist underneath the ice crust. This internal warmth comes from tidal heating caused by the gravitational forces of Jupiter and Jupiter’s other moons which pull Europa’s interior in different directions. Scientists believe similar tidal heating drives the volcanoes on another Jovian moon, Io. Seafloor hydrothermal vents have also been suggested as another possible energy source on Europa. On Earth, undersea volcanoes and hydrothermal vents create environments that sustain colonies of microbes. If similar systems are active on Europa, scientists reason that life might be present there too.

Among scientists there is a big push to get a mission to Europa underway. However this type of mission is competing for funding against NASA’s goal of returning to our own moon with human missions. The proposed Jupiter Icy Moon Orbiter (JIMO) a nuclear powered mission to study three of Jupiter’s moons, fell victim to cuts in science missions in NASA’s Fiscal Year 2007 Budget.

Ross has been designing and improving submarines for over 40 years, but this is the first time he’s designed a craft for use anywhere but on Earth.

“The biggest problem that I see with the robot submarine is being able to drill or melt its way through a maximum of 6 km of the ice, which is covering the surface,” said Ross. “However, the ice may be much thinner in some places. It may be that we will require a nuclear pressurized water reactor on board the robot submarine to give us the necessary power and energy to achieve this”

While Ross proposes using parachutes to bring the submarine to Europa’s surface, McKinnon points out that parachutes would not work in Europa’s almost airless atmosphere.

Ross has received very positive responses to his paper from friends and colleagues, he says, including notable British astronomer Sir Patrick Moore. Ross says his life has revolved around submarines since 1959 and he finds this new concept of a submarine on Europa to be very exciting.

McKinnon classifies the exploration of Europa as “extremely important.”

“Europa is a place is where we are pretty sure we have abundant liquid water, energy sources, and biogenic elements such as carbon, nitrogen, sulfur, phosphorus, etc,” he said. “Is there life, any kind of life, in Europa’s ocean? Questions don’t get much more profound.”

Written by Nancy Atkinson