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.

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.

ESA JUICE: Mission gets go ahead towards exploration of Jupiter

Artist's impression of the JUICE mission. 

Credit: ESA/AOES

The European Space Agency's JUICE (JUpiter ICy moons Explorer) mission has been given the green light to proceed to the next stage of development.

This approval is a milestone for the mission, which aims to launch in 2022 to explore Jupiter and its potentially habitable icy moons.

JUICE gained approval for its implementation phase from ESA’s Science Programme Committee during a meeting at the European Space Astronomy Centre near Madrid, Spain, on 19 and 20 November 2014.

Chosen by ESA in May 2012 to be the first large mission within the Cosmic Vision Programme JUICE is planned to be launched in 2022 and to reach Jupiter in 2030.

The mission will tour the giant planet to explore its atmosphere, magnetosphere and tenuous set of rings and will characterise the icy moons Ganymede, Europa and Callisto.

Detailed investigations of Ganymede will be performed when JUICE enters into orbit around it, the first time any icy moon has been orbited by a spacecraft.

During its lifetime, the mission will give us an unrivalled and in-depth understanding of the Jovian system and of these moons.

The scientific goals of the mission are enabled by its instrument suite. This includes cameras, spectrometers, a radar, an altimeter, radio science experiments and sensors used to monitor the plasma environment in the Jovian system.

In February 2013, the SPC approved the payload that will be developed by scientific teams from 16 European countries, the USA and Japan, through corresponding national funding.

At the November 2014 meeting of the SPC, the multilateral agreement for JUICE was also approved.

This agreement provides the legal framework for provision of payload equipment and ongoing mission support between funding agencies.

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

Jupiter's Red Spot is Chemical activated Sunburn

Research suggests effects of sunlight produce the color of Jupiter's Great Red Spot. 

The feature's clouds are much higher than those elsewhere on the planet, and its vortex nature confines the reddish particles once they form.

Image Credit: NASA/JPL-Caltech/ Space Science Institute

The ruddy color of Jupiter's Great Red Spot is likely a product of simple chemicals being broken apart by sunlight in the planet's upper atmosphere, according to a new analysis of data from NASA's Cassini mission.

The results contradict the other leading theory for the origin of the spot's striking color -- that the reddish chemicals come from beneath Jupiter's clouds.

The results are being presented this week by Kevin Baines, a Cassini team scientist based at NASA's Jet Propulsion Laboratory, Pasadena, California, at the American Astronomical Society's Division for Planetary Science Meeting in Tucson, Arizona.

Baines and JPL colleagues Bob Carlson and Tom Momary arrived at their conclusions using a combination of data from Cassini's December 2000 Jupiter flyby and laboratory experiments.

In the lab, the researchers blasted ammonia and acetylene gases, chemicals known to exist on Jupiter, with ultraviolet light, to simulate the sun's effects on these materials at the extreme heights of clouds in the Great Red Spot.

This produced a reddish material, which the team compared to the Great Red Spot as observed by Cassini's Visible and Infrared Mapping Spectrometer (VIMS).

They found that the light-scattering properties of their red concoction nicely matched a model of the Great Red Spot in which the red-colored material is confined to the uppermost reaches of the giant cyclone-like feature.

"Our models suggest most of the Great Red Spot is actually pretty bland in color, beneath the upper cloud layer of reddish material," said Baines.

"Under the reddish 'sunburn' the clouds are probably whitish or grayish." A coloring agent confined to the top of the clouds would be inconsistent with the competing theory, which posits that the spot's red color is due to upwelling chemicals formed deep beneath the visible cloud layers, he said.

If red material were being transported from below, it should be present at other altitudes as well, which would make the red spot redder still.

Jupiter is composed almost entirely of hydrogen and helium, with just a sprinkling of other elements. Scientists are interested in understanding what combinations of elements are responsible for the hues seen in Jupiter's clouds, as this would provide insights into the giant planet's make-up.

Spooky shadow play gives Jupiter a giant eye

Credit: NASA, ESA, and A. Simon (Goddard Space Flight Center)

The Hubble Space Telescope treats astronomers to gorgeous close-up views of the eerie outer planets but it's a bit of a trick when it seems like the planet's looking back at you!

In this view, the shadow of the Jovian moon Ganymede swept across the center of the Great Red Spot, a giant storm on the planet."

"This gave Jupiter the uncanny appearance of having a pupil in the center of a 10,000-mile-diameter "eye." Now if it blinks, we may really have to worry!

Hubble treats astronomers to gorgeous close-up views of the eerie outer planets, but it's a bit of a trick when it seems like the planet's looking back at you!

This happened on April 21, 2014, when Hubble was being used to monitor changes in Jupiter's immense Great Red Spot (GRS) storm.

During the exposures, the shadow of the Jovian moon Ganymede swept across the center of the GRS.

This gave the giant planet the uncanny appearance of having a pupil in the center of a 10,000-mile-diameter "eye."

Momentarily, Jupiter took on the appearance of a Cyclops planet! The shadows from Jupiter's four major satellites routinely cross the face of Jupiter.

This natural-colour picture was taken with Hubble's Wide Field Camera 3.

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.

Solar system simulation reveals planetary mystery

A snapshot of weather patterns around Mars, including blue-white ice clouds that are visible above the Red Planet’s Tharsis volcanoes. 

Credit: NASA/JPL-Caltech/MSSS

When we look at the Solar System, what clues show us how it formed?

We can see pieces of its formation in asteroids, comets and other small bodies that cluster on the fringes of our neighbourhood (and sometimes, fly closer to Earth.)

Are the orbits and sizes of the planets a natural byproduct of the formation, or are there features that happened because of rare events?

Scientists are focused on answering these questions to better understand how the Earth formed, and what this means for Earth-like planets around other stars.

For example, a new set of simulations showed that Mars is a rare planet. It can happen, but only in certain situations, at least, if the parameters of the simulations are correct.

Are these assumptions correct, or do other initial conditions need to be explored?

Finding the answers to these questions not only helps us understand where Mars comes from, but also our own planet.

This is interesting to astrobiologists because the Red Planet has extensive evidence of past water.

Results from the Opportunity, Spirit and Curiosity rovers on the Martian surface came across features that form in the presence of water, such as mineralised iron oxide known as hematite, or"blueberries," because of its shape.

"The formation of Mars is a long-standing problem. Most previous studies like this have not been able to reproduce an object with Mars' mass," said Rebecca Fischer, a doctoral candidate in geophysical sciences at the University of Chicago, who led the research.

"It is possible to reproduce Mars, but it only happens 5 percent of the time. If you only ran four simulations, you wouldn't see it happen," she says.

Fischer's work, called "Dynamics of the terrestrial planets from a large number of N-body simulations," appeared in the journal Earth and Planetary Science Letters in April.

More information: Rebecca A. Fischer, Fred J. Ciesla, "Dynamics of the terrestrial planets from a large number of N-body simulations," Earth and Planetary Science Letters, Volume 392, 15 April 2014, Pages 28-38, ISSN 0012-821X, dx.doi.org/10.1016/j.epsl.2014.02.011.

"Building the Terrestrial Planets: Constrained Accretion in the Inner Solar System." Sean N. Raymond, David P. O'Brien, Alessandro Morbidelli, Nathan A. Kaib arXiv:0905.3750 [astro-ph.EP] arxiv.org/abs/0905.3750

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.

Two dynamos drive Jupiter's magnetic field

Jupiter cut open: The magnetic field lines illustrate the high complexity of the magnetic field inside the planet, which, however, quickly decreases beyond the metallic layer (black line). 

On the surface, a dipolar part that is inclined by ten degrees with respect to the axis of rotation dominates. 

The thickness of the field lines is a measure of the local magnetic field strength. 

In the equatorial region, a jet produces bundles of field lines with a pronounced east-west orientation at the transition to the metallic layer. 

The coloured contours represent the radial surface field. Red indicates field lines directed outwards, blue inwards; green denotes a weak field. 

The colour coding of the sections represents the field in the east-west direction – red indicates eastwards, blue westwards. 

Credit: J. Wicht, MPS

Superlatives are the trademark of the planet Jupiter.

The magnetic field at the top edge of the cloud surrounding the largest member of the solar system is around ten times stronger than Earth's, and is by far the largest magnetosphere around a planet.

Just why this field has a similar structure to that of our own planet although the interiors of the two celestial objects have a completely different structure, has mystified researchers for a long time.

With the aid of the most detailed computer simulations to date, a team headed by the Max Planck Institute for Solar System Research in Göttingen has now succeeded in explaining the origin of the magnetic field deep inside the gaseous giant.

Magnetic fields are always generated when electric currents flow. The Earth is surrounded by a magnetic field because, deep in its interior, there is a circulating molten mass of iron and nickel.

This motion gives rise to electric currents that generate Earth's familiar dipolar magnetic field, in much the same way as a bicycle dynamo operates. Physicists call it the geo-dynamo, but how does the dynamo inside of Jupiter work?

Jupiter consists predominantly of hydrogen and helium.

Photos of the planet show coloured bands of cloud and gigantic tornados such as the Great Red Spot.

The temperature at the upper cloud boundary is minus 100 degrees Celsius, but temperature, pressure and electrical conductivity increase enormously with increasing depth.

At a depth of just under 10,000 kilometres and a pressure of several million atmospheres, the hydrogen even becomes conductive like a metal, an exotic state of matter which does not exist on Earth.

It is still unclear whether there is a rocky core at the centre of the planet; it could possibly amount to around 20 percent of the Jupiter radius, corresponding to 14,000 kilometres.

Previous computer simulations on the formation of the magnetic field had to greatly simplify this complex structure.

The upper gaseous region and the lower metallic region were treated separately, for example.

Thus, no computation correctly reproduced the strength and the form of the magnetic field as determined by space probes.

"Several colleagues assumed that certain physical quantities changed suddenly at the transition to the region of the metal-like conducting hydrogen," says project leader Johannes Wicht from the Max Planck Institute for Solar System Research in Göttingen, but new models from colleagues at the University of Rostock seem to prove that this is probably not the case.

The properties change gradually over the whole gas layer so that the separate treatment of the outer and inner region is hardly justified.

The important step forward here was the fact that, for the first time, the Göttingen-based physicists dealt with all regions of the planet in the same simulation.

To this effect, the Max Planck Society's huge Hydra supercomputer in Garching had to spend around six months on the computation.

The result was impressive: it portrayed Jupiter's magnetic field more or less as space probes had determined it in nature.

"The main part of the magnetic field, which looks so similar to Earth's magnetic field, is generated deep inside the planet, where the properties no longer change so strongly," says Wicht.

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

Voyager 3: Amateur timelapse of Jupiter 're-enacts' Voyager 1 1970 flyby

This animated gif shows Voyager 1′s approach to Jupiter during a period of over 60 Jupiter days in 1979. 

Credit: NASA

Back in the 1970′s when NASA launched the two Voyager spacecraft to Jupiter, Saturn, Uranus, and Neptune, we were all mesmerised by a movie created from Voyager 1 images of the movement of the clouds in Jupiter's atmosphere.

Voyager 1 began taking pictures of Jupiter as it approached the planet in January 1979 and completed its Jupiter encounter in early April.

During that time it took almost 19,000 pictures and many other scientific measurements to create the short movie, which you can see below, showing the intricate movement of the bright band of clouds for the first time.

Now, 35 years later a group of seven Swedish amateur astronomers achieved their goal of replicating the Voyager 1 footage, not with another flyby but with images taken with their own ground-based telescopes.

"We started this joint project back in December of 2013 to redo the NASA Voyager 1 flyby of Jupiter," amateur astronomer Göran Strand told reporters.

"During 90 days we captured 560 still images of Jupiter and turned them into 90 complete maps that covered the whole of Jupiter's surface."


Their newly released film, above details the work they did and the hurdles they overcame (including incredibly bad weather in Sweden this winter) to make their dream a reality.

They called their project "Voyager 3."

It is really an astonishing project and those of you who do image processing will appreciate the info in the video about the tools they used and how they did their processing to create this video.

The Swedish team of amateur astronomers who compiled the ‘Voyager 3′ project. 

Credit: Göran Strand

Scanning the skies for Exoplanets and Exomoons in other solar systems

The best prospect for habitable exomoons may be around gas giants. 

Credit: NASA

The first exoplanet was discovered in 1994.

Twenty years later, NASA's exoplanet catalog lists more than 1700 planets confirmed around other stars.

Most of these extra-solar-systems have been measured by changes in light spectra, in stellar motion or dust disks around stars.

Some exoplanets-more than 40 as of today-have even been directly photographed.

Jupiter's moons

One way or the other, we know that exoplanets are out there in abundance, in places we thought they would be and in places we didn't dream a planet could possibly exist. So what comes next? Finding moons.

Exomoons are naturally formed satellites circling around planets in other solar systems. Like the exoplanets themselves, we assume that exomoons are out there in relatively high abundance.

This assumption is based partly upon what we see around us in our own Solar System and partly upon our hypotheses about planetary formation.

Saturn's moons

This is what we observe in our own Solar System: moons are extremely common.

From Earth's one Moon to Jupiter's (currently known) fifty, every planet in the Solar System one astronomical unit or more from the Sun has a natural satellite.

Even Pluto, no longer officially classified as a planet, has a smaller companion circling around it.

Of note, the solid bodies such as Earth and Pluto have very few companions, while gaseous bodies Jupiter, Saturn, Uranus and Neptune have many.

Pluto and Charon

Furthermore, the masses of the Moon and Charon have a very specific relationship to Earth and Pluto in terms of mass: each satellite is about 10-2 the mass of their parent planet.

By contrast, the ratio of satellite masses to parent planet masses for the gas giants is very different: 10-4.

The differences in mass-ratio, how massive the moon is compared to the parent planet, and the differences in composition between the moons of solid planets and those of the gas giants led to a search for different formation scenarios for Earth's moon and the moons of the outer planets.

This is the current hypothesis: that there are two different methods of satellite formation at work in our Solar System.

Amy Barr Mlinar

Both methods were recently reviewed by Dr.Amy Barr Mlinar of Brown University at the Space Telescope Science institute Spring Symposium.

"This has been worked out starting about in the 1960's up through now," said Barr, "You have this [moon/planet] mass ratio of about 10-2 for solid planets, and a [moon/planet] mass ratio of about 10-4 for planets with a gaseous envelope."

Essentially, difference in mass ratios reflects the two completely different origins of our Moon and the satellites of Jupiter.

At the high end of the moon/planet mass ratio, 10-2 are the satellites of solid bodies (Earth and Pluto). These moons were formed from collisions.

Sometime in the distant past an object some large percentage of Earth's size struck the Earth, knocking material away that later coalesced into the Moon. The same is likely true of Charon, Pluto's companion.

Read the full article here

Jupiter's Great Red Spot is shrinking

In this comparison image the photo at the top was taken by Hubble's Wide Field Planetary Camera 2 in 1995 and shows the spot at a diameter of just under 21 000km; the second down shows a 2009 WFC3 photo of the spot at a diameter of just under 18 000km; and the lowest shows the newest image from WFC3 taken in 2014 with the spot at its smallest yet, with diameter of just 16 000km. 

Image courtesy NASA, ESA, and A. Simon (Goddard Space Flight Center). 

Jupiter's Great Red Spot is a churning anticyclonic storm. It shows up in images of the giant planet as a conspicuous deep red eye embedded in swirling layers of pale yellow, orange and white. Winds inside this Jovian storm rage at immense speeds, reaching several hundreds of kilometres per hour.

Historic observations as far back as the late 1800s gauged this turbulent spot to span about 41 000 kilometres at its widest point - wide enough to fit three Earths comfortably side by side. In 1979 and 1980 the NASA Voyager fly-bys measured the spot at a shrunken 23 335 kilometres across. Now, Hubble has spied this feature to be smaller than ever before.

"Recent Hubble Space Telescope observations confirm that the spot is now just under 16 500 kilometres across, the smallest diameter we've ever measured," said Amy Simon of NASA's Goddard Space Flight Center in Maryland, USA.

Amateur observations starting in 2012 revealed a noticeable increase in the spot's shrinkage rate. The spot's "waistline" is getting smaller by just under 1000 kilometres per year. The cause of this shrinkage is not yet known.

"In our new observations it is apparent that very small eddies are feeding into the storm," said Simon. "We hypothesised that these may be responsible for the accelerated change by altering the internal dynamics of the Great Red Spot."

Simon's team plan to study the motions of these eddies, and also the internal dynamics of the spot, to determine how the stormy vortex is fed with or sapped of momentum.

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.