NASA Galileo Image: Jupiter’s cratered moon, Callisto

The speckled object depicted here is Callisto, Jupiter’s second largest moon. 

This image was taken in May 2001 by NASA’s Galileo spacecraft, which studied Jupiter and its moons from 1995 until 2003.

Similar in appearance to a golf ball, Callisto is covered almost uniformly with pockmarks and craters across its surface, evidence of relentless collisions.

In fact, Callisto is the most heavily cratered object in the Solar System.

The moon is made up of equal parts of rock and ice, the brighter parts of Callisto’s surface are thought to be mainly water ice, whereas the darker patches are regions of highly eroded and ice-poor rocky material.

Callisto is roughly the same size as the planet Mercury, but only about a third of the mass. It is the outermost of Jupiter’s four large Galilean satellites, a group consisting of Io, Europa, Ganymede and Callisto.

It orbits relatively far away from Jupiter compared to these other satellites: it lies 1 880 000 km from the planet, roughly 26 times the radius of the planet itself.

While this in itself is not unusual, our Moon orbits at some 60 times Earth’s radius, the important thing is Callisto’s isolation from its neighbouring moons.

Callisto’s closest neighbour is Ganymede, which orbits 800 000 km closer to Jupiter.

This isolation means that Callisto does not experience any significant tidal forces from Jupiter that would tear at its structure.

It also does not show any signs of geological processes such as volcanism or plate tectonics, which we clearly see on moons that are involved in violent cosmic tugs-of-war with Jupiter, such as Io, Europa and Ganymede.

Callisto remains relatively intact and is a witness of the early Solar System: its surface is the oldest terrain, at a truly ancient four billion years.

This image is the only complete full-colour view of Callisto obtained by Galileo.

The spacecraft provided us with a great deal of information about the jovian system: as well as sending the first probe into the atmosphere of Jupiter, and measuring Jupiter’s composition and dynamics, it observed Io’s volcanism, sent back data supporting the idea of a liquid ocean on Europa, and probed the properties of Ganymede and the subject of this image,

Callisto. It also managed to observe the famous Comet Shoemaker–Levy 9 colliding with Jupiter in 1994.

The jovian system will be visited again in the not-too-distant future. In 2016, NASA’s Juno spacecraft will arrive at Jupiter and start to beam back images of the planet’s poles.

Later, ESA’s Juice, short for JUpiter ICy moons Explorer, planned for launch in 2022, will tour the system with the aim of making a breakthrough in our knowledge of the giant gaseous planet and its environs, especially the intriguing moons Ganymede, Europa and Callisto.

ESA GALILEO: Satellite Recovered and Transmittting Navigation Signals

ESA's Galileo satellites are placed in medium orbits, at 23 222 km altitude along three orbital planes so that a minimum of four satellites will be visible to user receivers at any point on Earth once the constellation is complete. 

Credit: ESA

ESA’s fifth Galileo satellite, one of two delivered into a wrong orbit by VS09 Soyuz-Fregat launcher in August, has transmitted its first navigation signal in space on Saturday 29 November 2014.

It has reached its new target orbit and its navigation payload has been successfully switched on.

A detailed test campaign is under way now the satellite has reached a more suitable orbit for navigation purposes.

Recovery

The fifth and sixth Galileo satellites, launched together on 22 August, ended up in an elongated orbit travelling up to 25 900 km above Earth and back down to 13 713 km.

A total of 11 manoeuvres were performed across 17 days, gradually nudging the fifth satellite upwards at the lowest point of its orbit.

As a result, it has risen more than 3500 km and its elliptical orbit has become more circular.

“The manoeuvres were all normal, with excellent performance both in terms of thrust and direction,” explained Daniel Navarro-Reyes, ESA Galileo mission analyst.

“The final orbit is as we targeted and is a tribute to the great professionalism of all the teams involved.”

The commands were issued from the Galileo Control Centre by Space Opal, the Galileo operator, at Oberpfaffenhofen in Germany, guided by calculations from a combined flight dynamics team of ESA’s Space Operations Centre, ESOC, in Darmstadt, Germany and France’s CNES space agency.

The commands were uploaded to the satellite via an extended network of ground stations, made up of Galileo stations and additional sites coordinated by France’s CNES space agency.

Satellite manufacturer OHB also provided expertise throughout the recovery, helping to adapt the flight procedures.

Until the manoeuvres started, the combined ESA–CNES team maintained the satellites pointing at the Sun using their gyroscopes and solar sensors. This kept the satellites steady in space but their navigation payloads could not be used reliably.

In the new orbit, the satellite’s radiation exposure has also been greatly reduced, ensuring reliable performance for the long term.

ESA Galileo: Soyuz launch glitch linked to frozen Hydrazine fuel pipe

A frozen fuel pipe in the upper stage of a Soyuz launcher likely caused the failure last month to place two European navigation satellites in orbit, a source close to the inquiry said Wednesday.

Confirming a report in French daily Le Monde, the source said investigators suspect a pipe containing hydrazine fuel, used by the Fregat upper stage to drive the satellites to their orbital slots, had frozen during launch.

The hydrazine pipes are located near a pipe that circulates ultra-cold liquid helium, the source said.

The two satellites, launched from Europe's base in Kourou, French Guiana, were intended to be the first two fully operational satellites in the new-generation navigation system Galileo.

30-satellite Galileo constellation. 

Credit: ESA

Two more satellites had been expected to be hoisted by the end of 2014, opening the way for a first phase of Galileo services in 2015, including applications for smartphones and in-car navigation and search-and-rescue location.

By 2017, according to the Galileo schedule, all 24 operational satellites would be in place.

Six backups would join the fleet by 2020, at which point the system would be fully operational.

Launched by a Russian-made Soyuz, the misplaced satellites should have been slotted into a circular orbit at an altitude of 23,500 kilometres (14,600 miles), inclined at 56 degrees to the equator.

Instead, they were placed in an useless elliptical orbit at a height of 17,000 kilometres (11,000 miles).

The failure adds to a catalogue of problems encountered by the 5.4-billion-euro ($7.2-billion) programme, designed to give the EU independence in satellite navigation from the US Global Positioning System (GPS).

Add caption

ESA Galileo IOV in orbit. 

Credit: ESA

Galileo, according to the project's defenders, will be more accurate and have a stronger signal, particularly in built-up areas, than its competitors.

Soyuz Rocket Launches European Galileo Satellites Into Wrong Orbit

The launch service provider Arianespace confirmed late Friday (Aug. 22) that two satellites for Europe's Galileo navigation network were released into the wrong orbit after launching aboard a Soyuz rocket from French Guiana.

It was not immediately clear whether the two satellites have enough fuel to make up for the orbit injection error.

Arianespace and European Space Agency officials initially heralded Friday morning's launch as a success, declaring the satellites healthy and claiming they were deployed into their targeted orbit approximately 23,500 kilometers, or 14,600 miles, above Earth.

The Russian-built Soyuz ST-B rocket carrying the Galileo navigation payloads blasted off at 8:27 a.m. EDT (1227 GMT) from the French-run Guiana Space Center in South America.

The Soyuz launcher's three booster stages gave way to a Russian Fregat-MT upper stage less than 10 minutes after liftoff.

The Fregat was programmed to fire two times to propel the Galileo satellites into a circular medium Earth orbit tilted at an angle of 55 degrees to the equator.



But U.S. military orbital tracking data indicated the satellites were flying in a lower orbit than planned. Officials confirmed a launch anomaly in a statement late Friday.

"Complementary observations gathered after separation of the Galileo FOC M1 satellites on Soyuz Flight VS09 have highlighted a discrepancy between targeted and reached orbit," Arianespace, the French launch services company, said in a statement.

Arianespace said investigations into the launch anomaly are underway and more information will be provided after a flight data analysis to be completed Saturday.

ESA Galileo Launch - Video

On 22 August, at 12:27 GMT/14:27 CEST, a Soyuz Flight VS09 launched Europe’s fifth and six Galileo satellites from Europe's Spaceport in Kourou, French Guiana.

These new satellites joined four Galileo satellites already in orbit, launched in October 2011 and October 2012 respectively.

This first quartet were ‘In-Orbit Validation’ satellites, serving to demonstrate the Galileo system would function as planned.

Now that work has been done, these ‘Full Operational Capability’ satellites are significant as the first of the rest of the Galileo constellation.

A steady stream of launches will follow to build the complete Galileo satellite constellation.

This deployment phase of the Galileo programme is being managed and funded by the European Commission, with ESA acting as design and procurement agent on behalf of the Commission.

ESA Galileo Soyuz Rocket Launch Cancelled - Bad Weather

A Soyuz rocket carrying a pair of Galileo In-Orbit Validation satellites lifts off from Europe'’s Spaceport in Sinnamary, 12km from Kourou, French Guiana on October 12, 2012

Foul weather has delayed the blast-off of two satellites for the Galileo navigation network, launch firm Arianespace said Thursday, as it announced 12 more launches starting next year to "step up" deployment of Europe's rival to GPS.

The liftoff of the fifth and sixth Galileo satellites, already delayed by more than a year, had been scheduled at 1231 GMT Thursday from the European space centre at Kourou in French Guiana on a Russian-made Soyuz rocket on Thursday.

But "unfavourable" weather intervened to cause an indefinite delay, Arianespace said in a statement.

"Another launch date will be decided depending on the evolution of the weather conditions in Kourou," it said.

Arianespace also announced it had signed a deal with the European Space Agency (ESA) to launch 12 more satellites "from 2015 onwards", for the EU-funded Galileo network.

The staggered launches aboard dedicated Ariane 5 ES rockets would "step up the deployment" of the navigation system, the company said, without specifying over what period they would happen.

The 5.4-billion-euro ($7.2-billion) Galileo constellation is designed to provide an alternative in case of signal failure on the existing US Global Positioning System and Russia's Glonass, and will have search and rescue capabilities.

ESA Galileo Deployment Phase - Video

On 21 August, at 12:31 UTC/14:31 CEST, a Soyuz rocket will launch the fifth and six of ESA's Galileo satellites from Europe's Spaceport in Kourou, French Guiana.

These are the first ‘Full Operational Capability’ satellites for the deployment phase of Galileo, following the so-called 'In Orbit Validation’ (IOV) phase, which allowed the European Space Agency (ESA) to make sure that the design of the Galileo system provided its expected performance both in space and on the ground.

Now it is time to build the full Galileo constellation, allowing full deployment to take place, the IOV satellites having paved the way for this European navigation programme, the first civilian system with worldwide services.

This phase of the Galileo programme is being managed and funded by the European Commission, with ESA acting as design and procurement agent on behalf of the Commission.

This video recalls the success of the In Orbit Validation phase and explains what will be the mission of these fifth and sixth Galileo satellites.

It includes an interview with Sylvain Loddo, ESA's Galileo Ground Segment Manager.

ESA Fifty Years of European Cooperation in Space

A new book by eminent historian John Krige details fifty years of European collaboration in space, from the origins of the space programmes of the early 1960s, to the many activities and rich complexity of ESA today.

The book, Fifty years of European cooperation in space: Building on its past, ESA shapes the future, charts the early moves by pioneering European scientific statesmen and governments to establish not one, but two organisations, European Space Research Organisation (ESRO) for science and later applications, and European Launcher Development Organisation (ELDO) for launchers.

The tight financial constraints on ESRO, the tribulations of ELDO's launcher, and a major tilt towards close technological cooperation with NASA in the early 1970s led to the formation of a single organisation in 1975, the European Space Agency, ESA.

EADS Ariane-5

As ESA embarked on developing a new European launcher under French leadership (EADS Ariane), and a human-rated laboratory for scientific experiments to fit in the US Space Shuttle's cargo bay under German leadership (Spacelab), its science programme was put on a secure institutional footing and it launched a number of applications programmes.

Early sketch of ESA Spacelab

The 1980s were marked by the spectacular success of Ariane, the consolidation of a human presence in space through Spacelab and collaboration in the International Space Station (ISS), the development of a new framework for rationalising space science and bruising disputes over engaging users to operate application satellites.

The global upheavals of the 1990s, the interest of the private sector in space, and an awareness of the value of space-based systems to civil society and military action on the ground obliged ESA to refashion itself again.

Russian Soyuz TMA-9M

New partnerships were forged. ESA's launcher fleet was expanded to include the Russian Soyuz and the Italian-led Vega.

A single European Astronaut Corps was created, and major new programmes for Earth observation; Copernicus - Global Monitoring for Environment and Security (GMES) and the European GPS satellite navigation (Galileo) were created in cooperation with the European Union.

The history of Europe's presence in space is above all a history of political will, of industrial development, and of the consolidation of extensive scientific, technological and managerial competencies to construct a global space power; one that could compete and collaborate from a position of strength with the US and the USSR/Russia, while adapting to the changing demands of a new geopolitical world order in the 21st century.

Fifty years of European cooperation in space: Building on its past, ESA shapes the future (EAN/ISBN: 97820701020297) is published by Les Editions Beauchesne (June 2014).

ESA Galileo: EU selects CGI to support Galileo Commercial Service Initiative

CGI has a long track record of supporting the European space industry, which includes having delivered the Constellation Control Facility that controls Galileo's 30 satellites, as well as developing software that underpins the missions of more than 200 individual satellites.

CGI has been awarded a contract to build the core infrastructure for the first demonstrator for the Galileo Commercial Service, part of the emerging European Global Navigation Satellite System (GNSS).

The contract was awarded by the European Commission Directorate General for Enterprise and Industry (DG ENTR).

When operational, Galileo satellites will take satellite navigation to a whole new level. Users will be able to rely on the service for their most critical positioning applications, especially when used in conjunction with other systems, such as GPS.

It will be especially useful in urban areas, on mountains and at high latitudes where GPS-only coverage can be intermittent.

The demonstrator application will show how Galileo can provide positioning services that are accurate to the centimetre, as well as its innovative position-authentication services could lead to further commercial uses.

Once complete, the demonstrator will be made available to other GNSS service providers to test across vertical markets, including transport, insurance and personal mobility.

The Galileo Commercial Service was introduced with the goal of creating a potential revenue source to support the future maintenance of EU satellite navigation services.

It provides added value to the Galileo Open Service with the expectation that new services will be based on its encrypted and guaranteed signal, which delivers a higher data throughput rate and increased positioning accuracy.

"The Commercial Service has many added benefits beyond its original designation as a potential revenue source for the Galileo system," said Steve Smart, vice president of the EU wing of the US corporation, Space, Defense and National Security at CGI in the UK.

"It will maximise the program's ability to provide the best navigation services possible to the public and commercial sectors, and will create economic value for the EU in general. We are proud to say we are playing a key role in this innovative process."

The European Commission DG ENTR is working in partnership with the European GNSS Agency (GSA) and the European Space Agency, in collaboration with member states.

The objective is to provide the operational Commercial Service, and its associated exploitation model, in the following years.

CGI has a long track record of supporting the European space industry, which includes having delivered the Constellation Control Facility that controls Galileo's 30 satellites, as well as developing software that underpins the missions of more than 200 individual satellites.

Laboratory models suggest that stretching forces shaped Ganymede's surface

An image of a tabletop-size analogue model (left) shows details of fault systems created by extension that visually match an image by spacecraft Galileo of faulted terrain on Ganymede (right). 

Credit: Left Image: Courtesy of Southwest Research Institute; 

Right Image: Courtesy of NASA/JPL SSI

Processes that shaped the ridges and troughs on the surface of Jupiter's icy moon Ganymede are likely similar to tectonic processes seen on Earth, according to a team of researchers led by Southwest Research Institute (SwRI).

To arrive at this conclusion, the team subjected physical models made of clay to stretching forces that simulate tectonic action. The results were published in Geophysical Research Letters.

Physical analogue models simulate geologic structures in laboratory settings so that the developmental sequence of various phenomena can be studied as they occur.

The team, including researchers from SwRI, Wheaton College, NASA's Jet Propulsion Laboratory and NuStar Energy LP, created complex patterns of faults in their models, similar to the ridge and trough features seen in some regions of Ganymede.

The models consisted of a "wet clay cake" material possessing brittle characteristics to simulate how the icy moon's lithosphere, the outermost solid shell, responds to stresses by cracking.

The laboratory models suggest that characteristic patterns of ridges and troughs, called grooved terrain on Ganymede, result from its surface being stretched.

"The physical models showed a marked similarity to the surface features observed on Ganymede," said co-author Dr. Danielle Wyrick, a senior research scientist in the SwRI Space Science and Engineering Division.

"From the experiments, it appears that a process in which the crust breaks into separate blocks by large amounts of extension is the primary mechanism for creating these distinct features."

"Physical analogue modeling allows us to simulate the formation of complex three-dimensional geological structures on Ganymede, without actually going to Ganymede," said co-author Dr. David Ferrill, director of the Earth, Material and Planetary Sciences Department in the SwRI Geosciences and Engineering Division.

"These scaled models are able to reproduce the fine geometric details of geologic processes, such as faulting, and to develop and test hypotheses for landscape evolution on planetary bodies."

SwRI researchers previously have used physical analog models to examine the process by which pit crater chains, a series of linear pits, or depressions, develop on Mars, and how magma in the Martian subsurface deforms the surface of the Red Planet.

More information: The paper, "Physical models of grooved terrain tectonics on Ganymede," by D.W. Sims, D.Y. Wyrick, D.A. Ferrill, A.P. Morris, G.C. Collins, R.T. Pappalardo and S.L. Colton, was published by Geophysical Research Letters, 16 June 2014, Volume 41, Issue 11, pages 3774–3778, DOI: 10.1002/2014GL060359

Arianespace Ariane 5 ECA Launches ASTRA 5B and Amazonas 4A

On Saturday, March 22, 2014 at 22:04 UTC, Arianespace carried out the 59th successful Ariane 5 launch in a row, orbiting two telecommunications satellites: ASTRA 5B for the Luxembourg-based operator SES, and Amazonas 4A for the Spanish operator Hispasat. 

ASTRA 5B also hosts an EGNOS (European Geostationary Navigation Overlay Service) payload for the EuropeanCommission.

59th successful launch in a row: Arianespace continues to deliver the world's most reliable launch service!

Today's successful mission, the 59th in a row for ESA's Ariane 5 ECA (Cryogenic Evolution Type A) launcher, confirms that Arianespace continues to set the standard for guaranteed access to space for all operators, whether national or international space agencies, private industry or governments.

Following the announcement of the orbital injection of the ASTRA 5B and Amazonas 4A satellites, Arianespace Chairman and CEO Stephane Israel said: "Today's successful launch, the 59th in a row for Ariane 5, confirms the unrivaled reliability and availability of the European launcher.

"We take particular pride in being able to offer this service excellence to two leading European operators, SES and Hispasat, both long-standing customers of Arianespace, as well as the European Commission, which has an EGNOS satellite navigation payload integrated on the ASTRA 5B satellite."

"For Arianespace and our family of the Ariane, Soyuz and Vega launchers, the watchword in 2014 will be 'Europe', following the launch of Athena-Fidus on February 6, a French-Italian spacecraft that meets both defense and homeland security requirements, and leading up to flagship programs deployed by the European Commission (Copernicus and Galileo) and the European Space Agency (ATV and IXV)."

"In addition, I would also like to express my thanks to Airbus Defence and Space (EADS), as the industrial prime contractor for Ariane 5, to the rest of the European space industry, the teams at Kourou, the Guiana Space Center, and our partners at CNES for today's magnificent success."

European Parliament adopts Copernicus: Earth Observation programme

The European Parliament on Wednesday gave its green light to Copernicus, the EU's new earth observation programme, according to a statement on its official website.


Copernicus, previously known as GMES (Global Monitoring for Environment and Security), is the European Programme for the establishment of a European capacity for Earth Observation.

The Copernicus Regulation will ensure the regular observation and monitoring of earth sub-systems, the atmosphere, oceans, and continental surfaces, and will provide reliable information in support of a broad range of environmental and security applications and decisions.

This programme, which still needs to be adopted by the European Council, defines Copernicus objectives, governance and funding of some 4.3 billion euros (5.97 billion U.S. dollars) for the period 2014-2020.

The European Commission welcomed the vote of the European Parliament on the Copernicus, said a statement publicised by the EU executive.

European Commission Vice President Antonio Tajani, responsible for industry and entrepreneurship said that "space is a priority for the European Union.

The budget for both European flagship space programmes, Copernicus and Galileo, for the next seven years is secured. Almost 12 billion euros will be invested in space technologies. "

The Copernicus programme is entering the operational phase after years of preparation. The next step is the launch of the first Copernicus satellite, Sentinel-1, beginning of April from Europe's Spaceport in French Guyana.

The data provided by this satellite will enable considerable progress in improving maritime security, climate change monitoring and providing support in emergency and crisis situations.

Under the administration of ESA and its management policies, Copernicus will also help Europe's enterprises creating new jobs and business opportunities.

Studies show that Copernicus could generate a financial benefit of some 30 billion euros and create around 50,000 jobs in Europe by 2030.

Global map of Ganymede, Jupiter's biggest moon

Making the map of Ganymede was a long and complex task. 

Some of the scientists behind the map were graduate students and postdocs at Brown University when the Galileo data began to arrive in the 1990s. 

Image courtesy U.S. Geological Survey.

Scientists, including Brown University geologists and students, have completed the first global geological map of Ganymede, Jupiter's largest moon and the largest in the solar system.

With its varied terrain and possible underground ocean, Ganymede is considered a prime target in the search for habitable environments in the solar system, and the researchers hope this new map will aid in future exploration.

Geoffrey Collins

The work, led by Geoffrey Collins, a Ph.D. graduate of Brown now a professor at Wheaton College in Massachusetts, took years to complete.

"It is very rewarding to see the results of all of our efforts here at Brown come together into this integrated global compilation that will now be used to plan the next phase of scientific exploration of the Galilean satellites," said Jim Head, the Scherck Distinguished Professor of Geological Sciences at Brown and one of the map's co-authors.

Global geologic map of Ganymede. Image credit: Collins G.C. et al.

The researchers combined images from the Voyager and Galileo spacecraft to put the map together. Voyager was the first mission to fly through the Jupiter satellite system and passed by the icy surface of Ganymede in 1979.

Those first images revealed a complex surface, segmented and fractured into dark and light terrain.

In 1995, the Galileo spacecraft was placed in orbit around Jupiter and began to return high-resolution images of the surface that help to understand many of the features seen at low-resolution by Voyager.

Jim Head

Head was a co-investigator on the Galileo's Solid State Imaging (SSI) experiment.

In that role, he and his team were responsible for planning the imaging sequences for Ganymede in order to identify and investigate the scientific targets of highest priority.

The team worked for several years to obtain the data necessary to make the global map.

"This was an amazing time," Head said. "Brown graduate and undergraduate students worked shoulder-to-shoulder in the Planetary Geosciences Laboratory in Lincoln Field Building, studying the newly acquired images and choosing new sites of scientific interest."

"The discoveries were daily and the adrenaline was surging as we rushed to collect our thoughts and plans, review them with the SSI Team, and get them uploaded to the spacecraft in time for the next encounter."

"I'm so glad all that work has paid off in the form of this detailed global map," Head said.

"It is equally rewarding to see that the Brown team has now moved on to positions of leadership in the planetary exploration research community."

The new geological map of Ganymede, published yesterday by the U.S. Geological Survey

ESA Video Trailer: Journey to a billion Suns

Journey to a billion suns is a 45-minute, 360 degree full-dome planetarium spectacular telling the fascinating story of mapping the Milky Way, from ancient times to ESA’s recently launched Gaia mission.

More information: www.planetariumshow.eu/journey-to-a-billion-suns/

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 Galileo: Galileo's secure service tested by Member States

Galileo IOV in orbit. Credit: ESA - P. Carril

EU Member States have begun their independent testing of the most accurate and secure signal broadcast by the four Galileo navigation satellites in orbit.

Transmitted on two frequency bands with enhanced protection, the Public Regulated Service (PRS) offers a highly accurate positioning and timing service, with access strictly restricted to authorised users.

"Galileo is in its In-Orbit Validation phase, planned to include experimental demonstrations of PRS capabilities in terms of positioning and access control," explained Miguel Manteiga Bautista, heading ESA's Galileo Security Office.

PRS access was initially considered for Galileo's Full Operational Capability phase, but it has been enabled in 2013 in response to the strong interest of Member States in this service.

To allow early access to PRS during the current phase, the European Commission and ESA began the joint project 'PRS Participants To IOV' (PPTI) in July 2012.

ESA ensured the availability of several tools developed under ESA contracts, including test receivers and other qualification equipment.

ESA also provided the critical knowhow and expertise required to conduct these experimental campaigns.

ESA's PRS Laboratory, based at the Agency's ESTEC technical centre in Noordwijk, the Netherlands, was used to provide training, demonstrations and sample data.

"As a result, Belgium, France, Italy and the UK have now performed independent PRS acquisition and positioning tests.

In parallel, ESA, through collaboration with Dutch and Italian authorities, is also conducting PRS fixed and mobile validation in several locations in the Netherlands and Italy," added Miguel Manteiga.

The PRS tests have demonstrated a current autonomous positioning accuracy below 10 m when in the correct geometrical configuration.

This is an impressive result considering the small number of Galileo satellites in orbit and the limited ground infrastructure so far deployed.

In the case of Italy, which has developed its own PRS receiver, the tests have already confirmed the feasibility of independent PRS receiver development and verification based on specifications provided by ESA.

"But the PPTI project is still ongoing in order to test more advanced functionalities this coming autumn and to run the first aeronautical PRS tests in collaboration with the Dutch authorities. Other Member States have also expressed their willingness to join the IOV PRS experimentation campaigns soon," concluded Miguel Manteiga.

The project is the first step to ensure the use of the PRS service as soon as it is operational. It will be complemented by the PRS Pilot Projects, focused on PRS applications, which are currently under definition in a common effort between the EU Member States, the European Commission, ESA and the European Global Navigation Satellite System Agency.

In addition to the qualification of the PRS service, these initiatives will allow the timely availability of competitive PRS receivers in Europe and the setting up of organisations in the Member States required to handle PRS.

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.

Jupiter's Hot Spots Explained - Video

Jupiter's Hot Spots NASA postdoctoral fellow David Choi discusses his study of dark features in Jupiter's atmosphere called "hot spots," and their connection to large-scale atmospheric waves.

Nasa can now re-examine the data garnered from the earlier Galileo probe, for new information.

Galileo plunged into Jupiter's crushing atmosphere on Sept. 21, 2003. The spacecraft was deliberately destroyed to protect one of its own discoveries - a possible ocean beneath the icy crust of the moon Europa.

Galileo was the first to measure Jupiter's atmosphere with a descent probe and the first to conduct long-term observations of the Jovian system from orbit.

It found evidence of subsurface saltwater on Europa, Ganymede and Callisto and revealed the intensity of volcanic activity on Io.

Windows Into Jupiter's moon Europa's Interior

This graphic of Jupiter's moon Europa maps a relationship between the amount of energy deposited onto the moon from charged-particle bombardment and the chemical contents of ice deposits on the surface in five areas of the moon (labeled A through E). 

Credit: NASA/JPL-Caltech/Univ. of Ariz./JHUAPL/Univ. of Colo.

The surface of Jupiter's moon Europa exposes material churned up from inside the moon and also material resulting from matter and energy coming from above.

If you want to learn about the deep saltwater ocean beneath this unusual world's icy shell -- as many people do, certainly those who are interested in possible extraterrestrial life -- you might target your investigation of the surface.

New analysis of observations made more than a decade ago by NASA's Galileo mission to Jupiter helps identify the deposits that have emanated from 'below' the surface rather than those deposited 'on' the surface.

In particular the report examines Sulphuric Acid Hydrate production on Europa's 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," said J. Brad Dalton of NASA's Jet Propulsion Laboratory, Pasadena, Calif., lead author of the report published recently in the journal Planetary and Space Science.

"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."

Europa is about the size of Earth's moon and, like our moon, keeps the same side toward the planet it orbits.

Picture a car driving in circles around a mountain with its left-side windows always facing the mountain.

Europa's orbit around Jupiter is filled with charged, energetic particles tied to Jupiter's powerful magnetic field.

Jupiter's Moon Io

Besides electrons, these particles include ions of sulphur and oxygen originating from volcanic eruptions on Io, a neighbouring Jupiter moon.

The magnetic field carrying these energetic particles sweeps around Jupiter faster than Europa orbits Jupiter, in the same direction: about 10 hours per circuit for the magnetic field versus about 3.6 days for Europa's orbit.

So, instead of our mountain-circling car getting bugs on the front windshield, the bugs are plastered on the back of the car by a "wind" from behind going nearly nine times faster than the car.

Europa has a "leading hemisphere" in front and a "trailing hemisphere" in back.

NASA's Galileo Satellite

Earlier studies had found more sulphuric acid hydrate being produced towards the center of the trailing hemisphere than elsewhere on Europa's surface, interpreted as resulting from chemistry driven by sulphur ions bombarding the icy surface.

Surface deposits in these areas are most likely to preserve the original chemical compounds that erupted from the interior.

Dalton suggests that any future spacecraft missions to Europa should target these deposits for study from orbit, or even attempt to land there.

Dalton stated "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."