NASA Cassini: Europa's atmosphere is thinner than previously thought

Data collected by NASA's Cassini spacecraft during its 2001 flyby of Jupiter shows that Europa's tenuous atmosphere is thinner than had been thought.

Europa is considered one of the most exciting destinations in the Solar System for future exploration because it shows strong indications of having an ocean beneath its icy crust.

Long, linear cracks and ridges crisscross Europa's surface, interrupted by regions of disrupted terrain where the surface ice crust has been broken up and re-frozen into new patterns.

Colour variations across the surface are associated with differences in geologic feature type and location.

The polar regions are bluer than the more equatorial latitudes, which appear more white. This colour variation is thought to be due to differences in ice grain size in the two locations.

Europa has a crust made up of blocks, which are thought to have broken apart and 'rafted' into new positions, as shown in the image on the left. 

Image Credit: NASA /JPL /University of Arizona

Europa is surrounded by very tenuous hot, excited gas. Indications of possible plume activity were reported in 2013 by researchers using NASA's Hubble Space Telescope.

Data collected by Cassini's ultraviolet imaging spectrograph (UVIS) as Cassini sped through the Jupiter system en route to Saturn, shows that most of the plasma around Europa originates not from the moon itself, but from volcanoes on the nearby moon Io.

Cassini's ultraviolet imaging spectrograph (UVIS)

The researchers calculate that Europa contributes 40 times less oxygen than previously thought to its surrounding environment, making it less likely that the moon is regularly venting plumes of water vapour high into orbit.

"Our work shows that researchers have been overestimating the density of Europa's atmosphere by quite a bit," said Don Shemansky, a Cassini UVIS team member with Space Environment Technologies, who led the study.

The moon's tenuous atmosphere, which was already thought to be millions of times thinner than Earth's atmosphere, is actually about 100 times less dense than those previous estimates.

The data shows no evidence of plume activity occurring at the time of the flyby, so if there is plume activity, it is likely intermittent.

Ongoing plume activity at Europa, as Cassini has observed at Saturn's moon Enceladus, would inject large amounts of water vapour into the area around Europa's orbit if the plumes were large enough, but that is not what UVIS observed.

"It is certainly still possible that plume activity occurs, but that it is infrequent or the plumes are smaller than we see at Enceladus," said Amanda Hendrix, a Cassini UVIS team member with the Planetary Science Institute, who co-authored the new study.

Missions that visited Jupiter prior to Cassini provided strong indications that Io is the major contributor of material to the environment around Jupiter, and indicated a hot, low density plasma surrounding Europa. The new results confirm that. "Io is the real monster here," Shemansky said.

"Europa is a complex, amazing world, and understanding it is challenging given the limited observations we have," said Curt Niebur, Outer Planets program scientist at NASA Headquarters.

"Studies like this make the most of the data we have and help guide the kinds of science investigations NASA should pursue in the future."

The Hubble Space Telescope is currently conducting an extensive six-month long survey looking for plume activity, and NASA is studying various possible Europa missions for future exploration.

Europa's salty lakes may harbour simple life forms - video

Jupiter's moon Europa is thought to have a vast ocean beneath its frozen surface.

NASA Cassini and other past missions have shown proof of salty water, which from our experience, has life-bearing potential.

Exploration of Europa is still stated as a high priority for NASA and is definitely a place of interest for science.

The video is presented by Kevin Hand, Astrobiologist and Deputy Chief Scientist at JPL.

The puzzling, fascinating surface of Jupiter's icy moon Europa looms large in this newly-reprocessed colour view, made from images taken by NASA's Galileo spacecraft in the late 1990s. 

This is the colour view of Europa from Galileo that shows the largest portion of the moon's surface at the highest resolution. 

The view was previously released as a mosaic with lower resolution and strongly enhanced colour. 

To create this new version, the images were assembled into a realistic colour view of the surface that approximates how Europa would appear to the human eye. 

The scene shows the stunning diversity of Europa's surface geology. Long, linear cracks and ridges crisscross the surface, interrupted by regions of disrupted terrain where the surface ice crust has been broken up and re-frozen into new patterns. 

Colour variations across the surface are associated with differences in geologic feature type and location. 

For example, areas that appear blue or white contain relatively pure water ice, while reddish and brownish areas include non-ice components in higher concentrations. 

The polar regions, visible at the left and right of this view, are noticeably bluer than the more equatorial latitudes, which look more white. 

This colour variation is thought to be due to differences in ice grain size in the two locations. Images taken through near-infrared, green and violet filters have been combined to produce this view. 

The images have been corrected for light scattered outside of the image, to provide a color correction that is calibrated by wavelength. 

Gaps in the images have been filled with simulated color based on the colour of nearby surface areas with similar terrain types. 

This global colour view consists of images acquired by the Galileo Solid-State Imaging (SSI) experiment on the spacecraft's first and fourteenth orbits through the Jupiter system, in 1995 and 1998, respectively.

Image scale is 2 miles (1.6 kilometers) per pixel. North on Europa is at right. 

Credit: NASA/JPL-Caltech/SETI Institute

Cubesats Payload on Europa Clipper Mission

Artist's impression of cubesats exploring Europa.

Credit: NASA/JPL-Caltech

NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif., has selected proposals from 10 universities to begin investigating the possible use of cubesats as auxiliary components to missions to Europa and beyond.

Cubesats are small, low cost space probes that can be used to collect scientific data by themselves or part of a “flock.”

They have been used extensively in the low-Earth orbit, providing a low-cost means for universities and institutions to carry out experiments in this microgravity environment.

As cubesat technology is maturing, so does the scope of their application.

So, as NASA steps up its plans for the Europa Clipper concept to visit the icy Jupiter moon, JPL has asked for cubesat proposals from universities that could complement the primary Clipper payload.

As we have a mission going to Europa, why not attach some cubesats for the ride?

NASA has outlined some key science objectives these axillary cubesats should be able to carry out, including “reconnaissance for future landing sites, gravity fields, magnetic fields, atmospheric and plume science, and radiation measurements.”

“We’ve seen some innovative and quite creative surprises among the CubeSat ideas submitted by these universities,” said Barry Goldstein, pre-project manager for the Europa Clipper mission.

“Using CubeSats for planetary exploration is just now becoming possible, so we want to explore how a future mission to Europa might take advantage of them.”

The chosen proposals have been awarded $25,000 each to develop their cubesat concepts to be included in the study, which is expected in the summer of 2015.

Europa is known to possess a sub-surface ocean of liquid water protected by a thick icy shell. As we learn more and more about this little world, our fascination with its life-giving potential is only amplified.

We now know that, combined with the oceans of water, nutrients are actively cycling to and from the surface. The icy surface appears to have plate tectonics.

Also, scientists believe there’s an abundance of oxygen in the ocean that’s heated by the tidal squishing of Europa’s orbit around Jupiter.

All of these factors point to a possibly habitable world where it has been hypothesized that multicellular life could thrive, but to test this hypothesis, we need to start sending missions to Europa so a close-up picture of its life-giving potential may be formulated, a mission that could be accelerated by the introduction of hitchhiking cubesats to the next big NASA missions to Jovian orbit.

Jupiter's Moon, Europa mimics Earth tectonics

False-colour image of Europa’s trailing northern hemisphere, where subduction zones are hypothesised (?) to exist. 

Credit: NASA /JPL /University of Arizona

Jupiter's icy moon Europa may have active tectonic plates similar to those that shape the Earth, which had long been thought unique in this respect, scientists said Sunday.

They used images captured by NASA's Galileo spacecraft, which orbited Jupiter and its moons from 1995 to 2003, to study the criss-cross of ridges and fractures on Europa's ice shell.

The moon, slightly smaller than the one orbitting Earth, has one of the youngest surfaces in the Solar System, implying "rapid recycling", said the team.

They found evidence that a piece of the surface had disappeared along a boundary between two ice plates, possibly when one sunk under the other.

They took this as evidence of surface material being recycled into the moon's interior, similar to parts of Earth's crust which sink into the underlying mantle at so-called subduction zones where tectonic plates converge.

This conceptual illustration of the subduction process (where one plate is forced under another) shows how a cold, brittle, outer portion of Europa’s 20-30 kilometer (roughly 10-20 mile) thick ice shell moved into the warmer shell interior and was ultimately subsumed. 

A low-relief subsumption band was created at the surface in the overriding plate, alongside which cryolavas may have erupted.

Image Credit: Noah Kroese, I.NK

The team studied an area of 134,000 square kilometres (51,700 square miles), using the images and a reconstruction of geological features.

They found that a 20,000 km2-portion of surface was missing.

"We propose that Europa's ice shell has a brittle, mobile, plate-like system above convecting warmer ice," they wrote in the journal Nature Geoscience.

"Hence, Europa may be the only Solar System body other than Earth to exhibit a system of plate tectonics."

Europa is one of the four largest moons of Jupiter, the fifth planet from the Sun and the largest in our Solar System.

Close-up view of a proposed zone of mid-ocean-ridge-like plate spreading on Europa (unrelated to the region studied in this work). 

This dilational band called Phaidra Linea, located in Europa’s trailing hemisphere near Argadnel Regio, shows internal striations related to spreading and bilateral symmetry about a central axis. Older geological features can be matched perfectly to either side of the spreading zone. 

The black strip in the center of the image is a narrow region where the images overlap and there is no image coverage. 

Credit: NASA/JPL

More information: Nature Geoscience, dx.doi.org/10.1038/ngeo2245

Giant Geysers Mysteriously Disappear on Jupiter's ice-covered moon Europa

This artist's concept image depicts a water vapour geyser erupting from the surface of Jupiter's icy moon Europa.

Credit: NASA/ESA/K. Retherford/SWRI

The huge plumes of water vapour erupting from Jupiter's ice-covered moon Europa seem to have vanished, and scientists aren't sure why.

In December 2013, researchers using NASA's Hubble Space Telescope announced that they had spotted evidence of geysers blasting into space from Europa's south polar region.

The discovery sparked a great deal of excitement among space scientists, as it suggested that a robotic flyby probe might be able to sample Europa's subsurface ocean of liquid water without even touching down.

However, follow-up Hubble observations in January and February of this year showed no signs of the plumes, which were estimated to reach about 125 miles (200 kilometers) into space.



There are several possible explanations, researchers said. For example, Europa's geysers may be sporadic, more like volcanoes here on Earth than the plumes blasting pretty much constantly from the south pole of Saturn's icy moon Enceladus, which harbours a subsurface ocean like Europa.

It's also possible that Europa's plumes are only visible to Hubble's instruments at certain times.

"It could be just the way that we use the auroral emissions coming from those plumes at the UV [ultraviolet] wavelengths of light that we use with Hubble," discovery team member Kurt Retherford, of the Southwest Research Institute in San Antonio, told reporters.

"These things depend on Jupiter's plasma environment," Retherford added.

"Maybe there were just a lot of particles, atoms, getting excited by electrons and ions in Europa's atmosphere, more so than at other times, and [they] just lit up the plumes more than they usually do."

Further, the plumes may sometimes simply be too small to see, Retherford said. (Enceladus' geysers have been observed relatively close-up by NASA's Saturn-orbiting Cassini spacecraft, but scientists are relying on the Earth-orbiting Hubble to study the features on Europa.)

This NASA image shows the location of water plumes on Jupiter's icy moon Europa as seen by NASA's Hubble Space Telescope in December 2012. 

The discovery marked the first time strong evidence of water geysers on Europa.

Credit: NASA/ESA/L. Roth/SWRI/University of Cologne

Another possibility is that the geysers don't exist, that the detection by Hubble, which was based primarily on observations the telescope made in December 2012, was an artifact or misinterpretation of some sort but Retherford stressed that this is unlikely.

"The best explanation still is plumes for that dataset, no doubt about it," he said.

Retherford and his colleagues are going to look for the plumes again soon. They'll train Hubble on Europa from November through April, in a more comprehensive attempt to confirm the existence of the water-vapour geysers and to characterise their behaviour.

"The question is the variability aspect of the plumes. Why do we see them in some observation sets and not others?" Retherford said.



Learning more about the plumes is a key priority for astrobiologists and for NASA, which is eyeing a mission to Europa in the mid-2020s.

The leading candidate for that mission at the moment is probably a probe called the Europa Clipper, which would make multiple flybys of the icy satellite.

"This is the kind of thing that could have a profound impact on how we explore Europa," Curt Niebur, outer planets program scientist at NASA headquarters, said during a NASA planetary sciences subcommittee meeting Wednesday (Sept. 3).

"With an ocean that is tens of kilometers below the ice, most likely, if you can have a plume that's possibly bringing material from that ocean up to orbit, well, that's going to affect how you explore," Niebur added.

Jupiter's Icy Moon Europa: Best Bet for Alien Life

Under a thick crust of ice, Europa might have an ocean warmed by tidal interactions with Jupiter. 

This tidal flexing could also produce a geologically active core that might in turn create hydrothermal vents on the ocean floor.

Credit: NASA/JPL/Ted Stryk

Jupiter's moon Europa doesn't look like a particularly inviting place for life to thrive; the icy satellite is nearly 500 million miles (800 million kilometers) from the sun, on average.

But beneath its icy crust lies a liquid ocean with more water than Earth contains. This ocean is shielded from harmful radiation, making Europa one of the solar system's best bets to host alien life.

That's one of the reasons Europa is so alluring to scientists. It has all the elements thought to be key for the origin of life: water, energy, and organic chemicals, the carbon-containing building blocks of life, scientists said at an event called "The Lure of Europa," held here last month.

"All the ingredients are there to make us think Europa is the next place to go," NASA Chief Scientist Ellen Stofan said at the event, which was organized by the Planetary Society, a nonprofit organization headed by scientist and TV host Bill Nye.



Just as a layer of ice over a pond allows the water beneath it to stay liquid through the freezing winter, Europa's icy crust shields its enormous ocean despite the moon's great distance from the sun.

As Europa travels around Jupiter, the massive planet bends and flexes the satellite, generating interior heat that keeps its water from freezing completely.

Beneath Europa's surface, active volcanoes may also heat the water, providing vents where bacterial life may thrive as it does on Earth.

"With that combination of volcanism and water, good things are going to happen," Stofan said.

Radio Signals from Jupiter Aids Search for Life and Liquid Water

This artist's impression shows Jupiter and its moon Europa using captured Jupiter and Europa images in visible light. 

The Hubble ultraviolet images showing the faint emission from the water vapour plumes have been superimposed, respecting the size but not the brightness of the plumes. 

Image courtesy NASA, ESA, and M. Kornmesser, University of California, Santa Cruz.

Powerful radio signals that Jupiter generates could be used to help researchers scan its giant moons for oceans that could be home to extraterrestrial life, according to a recent study submitted to the journal Icarus (In PDF format).

Jupiter, the largest planet in the Solar System, possesses 67 known moons, including three giant icy moons that might possess liquid oceans underneath their frozen surfaces.

Astrobiologists want to investigate Europa, Ganymede and Callisto for extraterrestrial life, as there is life virtually wherever there is liquid water on Earth.

Of Jupiter's three largest icy moons, Europa, which is roughly the size of Earth's moon, is favored as having the greatest potential to sustain life.

Magnetic readings captured by NASA's Galileo spacecraft provided compelling hints that it has an ocean, and radio scans by the probe suggest a water-rich layer beneath the surface between 50 to 105 miles (80 to 170 kilometers) thick.

Recent findings even suggest its ocean could be loaded with enough oxygen to support millions of tons worth of marine life.

Scientists would like to analyze Europa's ocean directly, perhaps with missions to bore into Europa's icy shell using heat to melt through the ice, whirling blades to clear away rocks, and robot subs to explore the ocean.

However, it remains uncertain how thick this shell is, complicating any plans to penetrate it.

Models of its thickness, based on the amount of heat the shell receives from the Sun and Europa itself, predict it to be roughly 18 miles (30 kilometers) thick.

In contrast, analyses of the Galileo spacecraft's data suggest the shell is no more than 9 miles (15 kilometers) thick, and maybe as little as 2.5 miles (4 kilometers) thick.

True colour and feature-highlighted photos of Europa. 

The bright feature towards the lower right of the disk is the 45 km diameter crater Pwyll. 

Credit: NASA.

Ice-penetrating radar is currently the most promising technique to directly confirm the existence of any ocean hidden within Jupiter's icy moons.

Radar works by transmitting radio signals, detecting any radio signals that reflect back, and analyzing these signals to deduce details about what they reflected off of, much like how a person might use a flashlight to illuminate objects hidden in the dark.

Ice and ground-penetrating radar systems look for signals that indicate buried objects and boundaries between layers.

In Europa's case, this means looking for the boundaries between the icy crust and any hidden ocean, and between such an ocean and Europa's rocky core.

To detect these oceans with ice-penetrating radar, low-frequency signals of less than 30 megahertz are needed to overcome radio wave absorption by the ice, as well as the unpredictable scattering of radio waves by the crinkled surfaces of these moons.

The low-frequency radio waves that researchers would like to use are decametric, meaning they have wavelengths tens of meters long.



Jupiter's Decametric waves
One problem with attempting ice-penetrating decametric radar on Jupiter's moons has to do with the powerful decametric radio bursts coming from Jupiter itself.

Altogether, these signals are more than 3,000 times stronger than any leaking into the Solar System from the rest of the galaxy.

Jupiter's decametric waves come from clouds of electrically charged particles trapped in Jupiter's magnetic field.

To overcome Jupiter's loud radio signals, a mission probing Jupiter's moons would need a relatively strong transmitter, a massive device that might be difficult to power and fit aboard the limited confines of a spacecraft.

Read the full article about how the research team plan to overcome the difficulties of Jupiter's natural emanation and generation of decametric waves.

More Information: A Passive Probe for Subsurface Oceans and Liquid Water in Jupiter's Icy Moons - Authors: Andrew Romero-Wolf, Steve Vance, Frank Maiwald, Essam Heggy, Paul Ries, Kurt Liewer

NASA RFI: External Concepts for mission to Europa - the oceanic Jovian moon

This image shows two views of the trailing hemisphere of Jupiter's ice-covered satellite, Europa. 

The left image shows the approximate natural colour appearance of Europa. 

The image on the right is a false-color composite version combining violet, green and infrared images to enhance colour differences in the predominantly water-ice crust of Europa. 

Credit: NASA/JPL/DLR

NASA has issued a Request for Information (RFI) to science and engineering communities for ideas for a mission to Europa that could address fundamental questions of the enigmatic moon and the search for life beyond Earth.

The RFI's focus is for concepts for a mission to Europa that costs less than $1 billion, excluding the launch vehicle that can meet as many of the science priorities as possible recommended by the National Research Council's 2011 Planetary Science Decadal Survey for the study of Europa.

"This is an opportunity to hear from those creative teams that have ideas on how we can achieve the most science at minimum cost," said John Grunsfeld, associate administrator for the NASA Science Mission Directorate at the agency's headquarters in Washington.

"Europa is one of the most interesting sites in our solar system in the search for life beyond Earth. The drive to explore Europa has stimulated not only scientific interest but also the ingenuity of engineers and scientists with innovative concepts."

NASA has studied a variety of mission designs and concepts in previous years and currently is funding the development of technologies that will be needed for the science instruments for a Europa mission.

Congress appropriated $80 million for this work in Fiscal Year 2014, and the Fiscal Year 2015 budget proposal requests an additional $15 million.

Previous scientific findings point to the existence of a liquid water ocean located under the moon's icy crust. This ocean covers Europa entirely and contains more liquid water than all of Earth's oceans combined.

The Decadal Survey deemed a mission to the Jupiter moon as among the highest priority scientific pursuits for NASA.

It lists five key science objectives in priority order that are necessary to improve our understanding of this potentially habitable moon.

The mission will need to:

• Characterise the extent of the ocean and its relation to the deeper interior
• Characterise the ice shell and any subsurface water, including their heterogeneity, and the nature of surface-ice-ocean exchange
• Determine global surface, compositions and chemistry, especially as related to habitability
• Understand the formation of surface features, including sites of recent or current activity, identify and characterise candidate sites for future detailed exploration
• Understand Europa's space environment and interaction with the magnetosphere.

Although Europa and Jupiter's other moons have been visited by other spacecraft, they were each limited to a single distant flyby of these satellites.

NASA's Galileo spacecraft, launched in 1989 by the space shuttle, was the only mission to make repeated visits to Europa, passing close by the moon fewer than a dozen times.

In December 2013, ESA /NASA's Hubble Space Telescope observed water vapor above the moon's frigid south polar region.

This provided the first strong evidence of water plumes erupting off the moon's surface, although researchers are still working to verify the existence of these plumes.

Any mission to Europa must take into account the harsh radiation environment that would require unique protection of the spacecraft and instruments.

In addition, spacecraft must meet planetary protection requirements intended to protect Europa's potentially habitable ocean.

These requirements are very strict and involve ensuring that a viable Earth organism is not introduced into the Europa ocean.

The RFI is not a request for proposal or formal procurement and therefore is not a solicitation or commitment by the government. Deadline to submit the mission concepts is May 30.

Jupiter's moon Europa: The Importance of Plumes

Plumes on the closest of the jovian moons, Io, are a common phenomenon. Credit: NASA/JPL

The Hubble Space Telescope is famous for finding black holes.

It can pick out thousands of galaxies in a patch of sky the size of a thumbprint.

The most powerful space telescope ever built, the Hubble provided evidence that the Universe isn't slowing down in its infinite rush into whatever lies beyond.

But the Hubble's cosmic firepower was recently put to a new purpose: searching for a billowing cloud of water vapor on Jupiter's moon Europa.

The plumes are a sign that extraterrestrial life could be lurking within our own Solar System.

Before we head way out there, we need to know a little about the eruptions happening at home.

Plumes: Warm and Nearby
On Earth, the plumes are a hallmark of energy in motion. Here, active geology often takes the form of pyroclastic eruptions. Pyro is Greek for "fire," while "clastic" derives from "broken."

Pyroclastic eruptions feature solid rock, semi-solid fragments and hot gases expelled from the mantle through areas of weakness in the crust.

They create the plumes of ash and smoke we typically associate with volcanos. Even when volcanos are underwater, as many are, they send up steaming columns of lava fragments, bits of rock and heated gas.

These underwater plumes of hot material rise hundreds of meters. The heated underwater plumes that make it to the surface of the ocean can be seen from space.

While these displays are impressive, not all that explodes from the Earth's crust is pyroclastic. Geysers are long columns of water.

Their bases lie close enough to the mantle to be heated by its 1,000° C (1,832 ° F) temperatures.

The heated water expands and rises, forcing its way to the surface. Once the water and steam reach the surface, the pressure falls, as does the plume of vapour, after inertia shoots it briefly into space.

In all of these formations, heated gases escape from the interior and reach the surface. There, they rapidly expand and cool, dissipating the fierce energies that drove them to erupt.

In this way, volcanism reflects the build-up of pressure within a planet or other large body on which it is known to occur.

In March of 2006, geysers were discovered spewing water from the surface of Enceladus, one of Saturn's icy moons.

Thus began a race to explain how a moon with surface temperatures of -330° Fahrenheit (-201° Celsius) could have active geology, and to discover if those geysers could signal a warm core for Enceladus and other icy moons.

More information: "Transient Water Vapour at Europa's South Pole." Lorenz Roth, Joachim Saur, Kurt D. Retherford, Darrell F. Strobel, Paul D. Feldman, Melissa A. McGrath, and Francis Nimmo. Science 10 January 2014: 343 (6167), 171-174.Published online 12 December 2013 [DOI: 10.1126/science.1247051]

Read the full article here

NASA Considers Ambitious Mission to Jupiter's Icy Moon Europa by 2025

Under a thick crust of ice, Europa might have an ocean warmed by tidal interactions with Jupiter. 

This tidal flexing could also produce a geologically active core that might in turn create hydrothermal vents on the ocean floor.

Credit: NASA/JPL/Ted Stryk

NASA hopes to launch a mission to the Jupiter moon Europa, perhaps the solar system's best bet to host alien life, a decade or so from now, officials announced Tuesday (March 4).

The White House's 2015 federal budget request, which was released Tuesday, allocates $15 million to help develop a mission to Europa, which harbors a potentially life-supporting ocean of liquid water beneath its icy shell.

"Europa is a very challenging mission operating in a really high radiation environment, and there's lots to do to prepare for it," NASA chief financial officer Beth Robinson told reporters Tuesday. "We're looking for a launch some time in the mid-2020s."



The $15 million — which represents a tiny fraction of the $17.5 billion allocated to the space agency in the 2015 request — would fund very early "pre-formulation" work for a potential Europa mission, Robinson added.

"I know people have asked about the total size [of the possible mission], and we're frankly just not sure at this point," she said, adding that agency officials will reach out to the scientific community to help map out the mission.

Galileo: Ocean Currents Shaping Europa's Icy Shell, Critical for Potential Habitats

Zonal flows in Europa-like ocean simulation. 

Image credit: University of Texas Institute for Geophysics.

In a finding of relevance to the search for life in our solar system, researchers at the University of Texas at Austin's Institute for Geophysics, the Georgia Institute of Technology, and the Max Planck Institute for Solar System Research have shown that the subsurface ocean on Jupiter's moon Europa may have deep currents and circulation patterns with heat and energy transfers capable of sustaining biological life.

Scientists believe Europa is one of the planetary bodies in our solar system most likely to have conditions that could sustain life, an idea reinforced by magnetometer readings from the Galileo spacecraft detecting signs of a salty, global ocean below the moon's icy shell.

Without direct measurements of the ocean, scientists have to rely on magnetometer data and observations of the moon's icy surface to account for oceanic conditions below the ice.

Regions of disrupted ice on the surface, known as chaos terrains, are one of Europa's most prominent features.

As lead author Krista Soderlund and colleagues explain in this week's online edition of the journal Nature Geosciences, the chaos terrains, which are concentrated in Europa's equatorial region, could result from convection in Europa's ice shell, accelerated by heat from the ocean.

The heat transfer and possible marine ice formation may be helping form diapirs, or warm compositionally buoyant plumes of ice that rise through the shell.

In a numerical model of Europa's ocean circulation, the researchers found that warm rising ocean currents near the equator and subsiding currents in latitudes closer to the poles could account for the location of chaos terrains and other features of Europa's surface.

Such a pattern coupled with regionally more vigorous turbulence intensifies heat transfer near the equator, which could help initiate upwelling ice pulses that create features such as the chaos terrains.

"The processes we are modeling on Europa remind us of processes on Earth," says Soderlund, where a similar process has been observed in the patterns creating marine ice in parts of Antarctica.

The current patterns modeled for Europa contrast with the patterns observed on Jupiter and Saturn, where bands of storms form because of the way their atmospheres rotate.

The physics of Europa's ocean appear to have more in common with the oceans of the "ice giants" Uranus and Neptune, which show signs of three-dimensional convection.

"This tells us foundational aspects of ocean physics," notes co-author Britney Schmidt, assistant professor at the Georgia Institute of Technology."

"More importantly, adds Schmidt, if the study's hypothesis is correct, it shows that Europa's oceans are very important as a controlling influence on the surface ice shell, offering proof of the concept that ice-ocean interactions are important to Europa.

"That means more evidence that the ocean is there, that it's active, and there are interesting interactions between the ocean and ice shell," says Schmidt, "all of which makes us think about the possibility of life on Europa."

Soderlund, who has studied icy satellites throughout her science career, looks forward to the chance to test her hypothesis through future missions to the Jovian system.

The European Space Agency's JUICE mission (JUpiter ICy moons Explorer) will give a tantalizing glimpse into the characteristics of the ocean and ice shell through two flyby observations.

NASA's Europa Clipper mission concept, under study, would complement the view with global measurements.

Soderlund says she appreciates the chance "to make a prediction about Europa's subsurface currents that we might know the answer to in our lifetimes - that's pretty exciting."

New computer model may explain moon Europa's chaotic terrain

This rendering shows the temperature field in a simulation of Europa’s global ocean dynamics, where hot plumes (red) rise from the seafloor and cool fluid (blue) sinks downward from the ice-ocean interface. 

More heat is delivered to the ice shell near the equator where convection is more vigorous, consistent with the distribution of chaos terrains on Europa. 

Credit: Model image created by K. M. Soderlund with the image of Europa taken from NASA/JPL/University of Arizona

A team of researchers at the University of Texas with assistance from a computer modeler at the Max Planck Institute in Germany has put together a computer model that might just explain the peculiar surface of Jupiter's moon Europa.

In their paper published in the journal Nature Geoscience, the team suggests the odd surface terrain patterns likely come about due to convection. Jason Goodman of Wheaton College offers a perspective on the researchers' findings in a News & Views piece printed in the same journal.

The NASA space probe Voyager flew past Jupiter and its moons in 1979, and in so doing, set off a debate about the nature of the surface of one such moon, Europa, that has continued to this day—why is the surface so smooth, and why are there odd rough patches covering nearly 40 percent of its surface?

Scientists agree that the general smoothness is likely due to the existence of water beneath the icy surface—the lack of craters indicates a surface that is able to heal itself after impacts.

Less of a consensus has been found regarding the rough patches, however, which scientists call "chaotic terrain."

Galileo

In this new study, the researchers used data from hydro-systems here on Earth as well as data from both Voyager and the Galileo spacecraft (which detected a magnetic field) to create what they believe is a reasonable model of a convection process working beneath the icy shell of Europa's surface.

Some have suggested Europa's surface gets its unique features due to the pull of gravity from Jupiter—others have suggested the sun plays a role.

Such theories have not held much weight however, as there is little evidence to suggest that either could account for the chaotic terrain.

Instead, the modelers suggest, it's due to convection driven by heat from the interior of the moon itself.

Their model shows, they write that currents beneath the ice tend to deliver heat primarily to the equatorial regions of the surface which in turn causes constant heating, melting and refreezing—resulting they say, in the chaotic terrain that we are able to observe.

More information: Ocean-driven heating of Europa's icy shell at low latitudes, Nature Geoscience (2013) DOI: 10.1038/ngeo2021

ESA and Russia Plan Probe Landing on Jupiter's Moon, Ganymede

An artist's illustration of the JUpiter ICy moons Explorer spacecraft in the Jovian system. The mission will launch in 2022 and arrive at Jupiter in 2030 to study the planet and its largest moons.

CREDIT: ESA/AOES

A Russian probe being designed to land on Ganymede, Jupiter's largest moon, could launch toward the gas giant with a European spacecraft being developed to explore Jupiter's icy ocean-covered satellites, according to European space officials.

The benefits of such a joint launch arrangement, including sharing reconnaissance and mapping from Europe's Jupiter Icy Moons Explorer (JUICE), are not lost on scientists. But more Earthly concerns, such as government finances and the realities of technical developments, could thwart the proposal.

"It all depends on if the Russians are ready to fly at the same time as us," said Alvaro Gimenez Canete, director of the European Space Agency (ESA)'s science and robotic exploration programs.

The solar system's giant
JUICE is scheduled to launch in 2022 and arrive at Jupiter in 2030, entering orbit around the huge planet and making repeated flybys of three of its largest moons — Ganymede, Callisto and Europa.

In September 2032, the European spacecraft will arrive at Ganymede, becoming the first probe to enter orbit around the moon of another planet. Equipped with radar, a mapping camera and other instruments, JUICE will measure the thickness of global ice sheets covering Jupiter's moons and produce terrain and mineral maps of Ganymede.

Such data will prove to be a rich resource not only for researchers, but also for engineers planning missions to explore Ganymede's surface and study what lies beneath the moon's crust of ice, Gimenez told reporters at the Paris Air Show this week.

"Russia's plan is to implement a Ganymede Lander, which is a very ambitious mission," said Fabio Favata, head of ESA's science planning and community coordination office, which oversees the strategic direction of the space agency's space science programs.

Favata said the Russian mission, for now known by scientists simply as the Ganymede Lander, has captured the interest of Europe's planetary science community.

An illustration of Russia's planned Ganymede lander that could explore the Jupiter moon as part of the European Space Agency's Jupiter Icy Moons Explorer mission.

CREDIT: ESA/Roscosmos

Europa or Ganymede?

Russian mission planners initially proposed the lander to target Europa, another of Jupiter's moons with a frozen crust thinner than the ice cap covering Ganymede. After a NASA mission to orbit Europa never materialized, Russia retooled the project to focus on Ganymede, falling in line with the goals of Europe's Jupiter mission.

There are numerous advantages of landing on Ganymede as opposed to Europa. The radiation environment at Ganymede is less severe than at Europa, which lies closer to Jupiter; this is one of the reasons ESA picked Ganymede as the destination for JUICE, Gimenez said.

According to presentations at a workshop hosted by Russia's Space Research Institute in Moscow in March, Russian scientists say mapping and reconnaissance of Ganymede are required before any attempted landing. Russia's concept for the mission, which assumes no international collaboration for now, includes an orbiter and a lander to be dispatched to Ganymede in 2023 or 2024.

The scope of a potential partnership between Europe and Russia on robotic Jupiter exploration ranges from no collaboration to a completely merged program in which JUICE and the Ganymede Lander would launch from Earth together on the journey into the outer solar system.

Another option — perhaps the most likely, scientists say — is a loose collaboration involving complementary scientific goals, shared development of science instruments, and the use of the JUICE mission to help select a landing site on Ganymede.

Where to Look for Life on Jupiter's Moon Europa

These images show the trailing hemisphere of Jupiter's moon Europa taken by the Galileo spacecraft at a distance of about 677,000 km. 

The left image shows Europa in approximately true colour and the right image shows Europa in enhanced colour to bring out details. 

The bright feature towards the lower right of the disk is the 45 km diameter crater Pwyll.

CREDIT: NSSDC Photo Gallery

Jupiter's icy moon Europa is thought to be hiding a saltwater ocean beneath its thick outer crust, an exciting prospect for scientists searching for extra-terrestrial life in our solar system.

A fresh look at decade-old observations from NASA's Galileo mission could help researchers pick the ideal spot to probe Europa in the future to get an idea of what's below its surface.

J. Brad Dalton

"We have found the regions where charged electrons and ions striking the surface would have done the most, and the least, chemical processing of materials emplaced at the surface from the interior ocean," J. Brad Dalton of NASA's Jet Propulsion Laboratory, said in a statement.

"That tells us where to look for materials representing the most pristine ocean composition, which would be the best places to target with a lander or study with an orbiter."

Jupiter has the most powerful magnetic field of all the planets in our solar system at nearly 20,000 times the strength of Earth's.

This field traps electrons and other charged particles including ions of sulfur and oxygen spewed from volcanic eruptions on Io, a neighboring Jovian moon.

The particles in this field rush around Jupiter at a rate of about 10 hours per circuit, while Europa, which is about the size of Earth's moon, takes 3.6 days to orbit the planet in the same direction.

And like Earth's moon, Europa has a far side that is always facing away from Jupiter's surface. This means it also has a back side that is constantly being smacked with speeding particles, which takes a toll on the surface chemistry.

By looking at observations from Galileo's near infrared mapping spectrometer, Dalton and colleagues saw that there tended to be more frozen sulphuric acid at parts of Europa that had been more heavily bombarded with electrons and sulfur ions.

"If you are interested in the composition and habitability of the interior ocean, the best places to study would be the parts of the leading hemisphere we have identified as receiving the fewest electrons and having the lowest sulfuric acid concentrations," Dalton said.

The researchers believe these places are the most likely to have chemical compounds that originated from Europa's interior, and are not the result of surface chemical reactions.

"The darkest material, on the trailing hemisphere, is probably the result of externally-driven chemical processing, with little of the original oceanic material intact," Dalton added.

"While investigating the products of surface chemistry driven by charged particles is still interesting from a scientific standpoint, there is a strong push within the community to characterize the contents of the ocean and determine whether it could support life. These kinds of places just might be the windows that allow us to do that."

NASA's Galileo spacecraft was launched in 1989 and finally arrived at Jupiter's system in 1995. It spent eight years circling the solar system's most giant planet before its mission ended in 2003.

The new research was detailed recently in the journal Planetary and Space Science.

NASA Cassini Finds Hints of Geological Activity on Saturn Moon Dione

The NASA Cassini spacecraft swooped in for a close-up of the cratered, fractured surface of Saturn's moon Dione in this image taken during the spacecraft's Jan. 27, 2010, non-targeted flyby.

Image credit: NASA /JPL-Caltech /Space Science Institute.

From a distance, most of the Saturnian moon Dione resembles a bland cueball.

Thanks to close-up images of a 500-mile-long (800-kilometer-long) mountain on the moon from NASA's Cassini spacecraft, scientists have found more evidence for the idea that Dione was likely active in the past. It could still be active now.

Bonnie Buratti

"A picture is emerging that suggests Dione could be a fossil of the wondrous activity Cassini discovered spraying from Saturn's geyser moon Enceladus or perhaps a weaker copycat Enceladus," said Bonnie Buratti of NASA's Jet Propulsion Laboratory in Pasadena, Calif., who leads the Cassini science team that studies icy satellites.

"There may turn out to be many more active worlds with water out there than we previously thought."

Other bodies in the solar system thought to have a subsurface ocean - including Saturn's moons Enceladus and Titan and Jupiter's moon Europa - are among the most geologically active worlds in our solar system.

They have been intriguing targets for geologists and scientists looking for the building blocks of life elsewhere in the solar system.

The presence of a subsurface ocean at Dione would boost the astrobiological potential of this once-boring iceball.

Hints of Dione's activity have recently come from Cassini, which has been exploring the Saturn system since 2004.

This image, which is composed of data obtained by NASA's Cassini spacecraft, shows the topography of a mountain known as Janiculum Dorsa on the Saturnian moon Dione. 

Image credit: NASA/JPL-Caltech/SSI/Brown

The spacecraft's magnetometer has detected a faint particle stream coming from the moon, and images showed evidence for a possible liquid or slushy layer under its rock-hard ice crust.

Other Cassini images have also revealed ancient, inactive fractures at Dione similar to those seen at Enceladus that currently spray water ice and organic particles.

The mountain examined in the latest paper -- published in March in the journal Icarus -- is called Janiculum Dorsa and ranges in height from about 0.6 to 1.2 miles (1 to 2 kilometers).

The moon's crust appears to pucker under this mountain as much as about 0.3 mile (0.5 kilometer).

Noah Hammond

"The bending of the crust under Janiculum Dorsa suggests the icy crust was warm, and the best way to get that heat is if Dione had a subsurface ocean when the ridge formed," said Noah Hammond, the paper's lead author, who is based at Brown University, Providence, R.I.

Dione gets heated up by being stretched and squeezed as it gets closer to and farther from Saturn in its orbit.

With an icy crust that can slide around independently of the moon's core, the gravitational pulls of Saturn get exaggerated and create 10 times more heat, Hammond explained.

Other possible explanations, such as a local hotspot or a wild orbit, seemed unlikely.

Scientists are still trying to figure out why Enceladus became so active while Dione just seems to have sputtered along.

Perhaps the tidal forces were stronger on Enceladus, or maybe the larger fraction of rock in the core of Enceladus provided more radioactive heating from heavy elements.

Read more here