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.
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.
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
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