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

What is beneath the cracked surface of Pluto's moon Charon?

An artist’s concept of Pluto as viewed from the surface of one its moons. 

Pluto is the large disk at the center of the image. Charon is the smaller disk to the right. 

Credit: NASA, ESA and G. Bacon (STScI)

Is there evidence of an ocean-past or present-waiting to surprise us on Charon?

It isn't impossible. In fact, it might be likely.

What used to be the smallest planet in our solar system has, comparatively, the biggest moon.

Pluto, now classified as a dwarf planet, has a moon, Charon, almost 1/8th its own mass and almost half its physical volume.

Our Moon, by comparison, has about 1% of the Earth's mass and only 2% of its volume.

Charon is so large compared to Pluto that some astronomer's consider the two to be a sort of binary dwarf-planet system, as opposed to a moon-and-planet system.

Both Charon and our Moon are believed to have formed in the same way: when they were knocked off their parent planets.

Enormous collisions liquified parts of the Earth and Pluto. The debris was thrown into orbit where it later cooled.

In the process of cooling into solid bodies around the Earth and Pluto, the Moon and Charon became locked to their parent planets' orbits.

That locking of the planets to moons results in tides: here on Earth, on the Moon, and, we believe, on Pluto and Charon.

An analysis by scientists at Goddard suggests that tides on Pluto and Charon could have been especially high as Charon cooled.

This is because the part of Pluto knocked into orbit didn't get very far. Charon formed incredibly close to Pluto: only 19,000 km (12,000 miles) away.

By comparison, our Moon is currently 384,000 km (238,855 mi) from Earth. Initially, the orbit might not have been very circular, either: it might have been more eccentric or elliptical-shaped.

Eccentrically-moving, close-by Charon would have pulled on Pluto, and Pluto would have pulled back, resulting in heating of both planets and, maybe, an ocean under Charon's ice shell.

Alyssa Rhoden

Depending on exactly how Charon's orbit evolved, particularly if it went through a high-eccentricity phase, there may have been enough heat from tidal deformation to maintain liquid water beneath the surface of Charon for some time," said Alyssa Rhoden of NASA's Goddard Space Flight Center in Greenbelt, Maryland.

"Using plausible interior structure models that include an ocean, we found it wouldn't have taken much eccentricity (less than 0.01) to generate surface fractures like we are seeing on Europa."

Artist impression of the New Horizons spacecraft as it approached Jupiter en route to Pluto. 

Credit: NASA

On icy moons like Europa and Enceladus, tidal forces exerted by their parent planets cause massive surface cracks to form.

Those cracks are easily appreciated by passing spacecraft. According to Rhoden and colleagues' model, Charon's surface should be similarly cracked.

We expect to see evidence of this fractured surface geology as the New Horizons spacecraft approaches Pluto. New Horizons will pass directly over Pluto and Charon, briefly, on July 15th 2015.

Charon was discovered thirty-five years ago, in 1978, but well-photographed for the first time by New Horizons in 2013.

With the 2015 close-up just around the corner, scientists are working swiftly to make best use of surface photographs returned by the spacecraft.

New Horizons will give us the ability to resolve objects as small as a football field on part of the surface of Pluto and Charon.

With pictures of that detail and models such as this one, we may be able to look backwards in time to determine details about both bodies, such as how thick their ice shells were when they formed.

Studying patterns of fractures in Charon's surface is critical to building accurate models of the ice shell and layers beneath.

"Our model predicts different fracture patterns on the surface of Charon depending on the thickness of its surface ice, the structure of the moon's interior and how easily it deforms, and how its orbit evolved," said Rhoden.

"By comparing the actual New Horizons observations of Charon to the various predictions, we can see what fits best and discover if Charon could have had a subsurface ocean in its past, driven by high eccentricity."

The oceans of certain icy moons with surface fractures are considered to be places where extraterrestrial life might be found.

Like Charon, Europa and Enceladus are very cold and very distant from the sun. In all three cases, the formation and maintenance of life would depend upon a reliable energy source as well as elements that can participate in the chemistry of life, such as carbon, nitrogen, and phosphorus.

New Horizons Long Range Reconnaissance Imager (LORRI) composite image showing the detection of Pluto’s largest moon, Charon. 

When these images were taken on July 1 and July 3, 2013, the New Horizons spacecraft was still about 550 million miles (880 million kilometers) from Pluto.

On July 14, 2015, the spacecraft is scheduled to pass just 7,750 miles (12,500 kilometers) above Pluto’s surface, where LORRI will be able to spot features about the size of a football field. 

Credit: NASA /Johns Hopkins University Applied Physics Laboratory /Southwest Research Institute (SRI)

It is unknown if a potential ocean on Charon may have harbored these ingredients or if the ocean there existed for long enough for life to form.

The same questions apply to any ancient ocean on any moon in our Solar System or any other. The first step on Charon is to find the fractures, and then go looking for the warmth that liquid water.

"Since it's so easy to get fractures, if we get to Charon and there are none, it puts a very strong constraint on how high the eccentricity could have been and how warm the interior ever could have been," said Rhoden.

"This research gives us a head start on the New Horizons arrival, what should we look for and what can we learn from it. We're going to Pluto and Pluto is fascinating, but Charon is also going to be fascinating."

Meteorites yield clues to Martian early atmosphere - Sulphur

A microscope reveals colorful augite crystals in this 1.3 billion-year-old meteorite from Mars, which researchers studied to understand the red planet's atmospheric history. 

Credit: James Day

Geologists who analyzed 40 meteorites that fell to Earth from Mars unlocked secrets of the Martian atmosphere hidden in the chemical signatures of these ancient rocks.

Their study, published April 17 in the journal Nature, shows that the atmospheres of Mars and Earth diverged in important ways very early in the 4.6 billion year evolution of our solar system.

The results will help guide researchers' next steps in understanding whether life exists, or has ever existed, on Mars and how water—now absent from the Martian surface—flowed there in the past.

Heather Franz

Heather Franz, a former University of Maryland (UMD) research associate who now works on the Curiosity rover science team at the NASA Goddard Space Flight Center, led the study with James Farquhar, co-author and UMD geology professor.

The researchers measured the sulfur composition of 40 Mars meteorites—a much larger number than in previous analyses. Of more than 60,000 meteorites found on Earth, only 69 are believed to be pieces of rocks blasted off the Martian surface.

The meteorites are igneous rocks that formed on Mars, were ejected into space when an asteroid or comet slammed into the red planet, and landed on Earth.

James Farquhar

The oldest meteorite in the study is about 4.1 billion years old, formed when our solar system was in its infancy. The youngest are between 200 million and 500 million years old.

Studying Martian meteorites of different ages can help scientists investigate the chemical composition of the Martian atmosphere throughout history, and learn whether the planet has ever been hospitable to life.

Mars and Earth share the basic elements for life, but conditions on Mars are much less favourable, marked by an arid surface, cold temperatures, radioactive cosmic rays, and ultraviolet radiation from the Sun.

Still, some Martian geological features were evidently formed by water – a sign of milder conditions in the past.

Scientists are not sure what conditions made it possible for liquid water to exist on the surface, but greenhouse gases released by volcanoes likely played a role.

Sulphur, which is plentiful on Mars, may have been among the greenhouse gases that warmed the surface, and could have provided a food source for microbes.

Because meteorites are a rich source of information about Martian sulphur, the researchers analyzed sulfur atoms that were incorporated into the rocks.

In the Martian meteorites, some sulphur came from molten rock, or magma, which came to the surface during volcanic eruptions.

Volcanoes also vented sulphur dioxide into the atmosphere, where it interacted with light, reacted with other molecules, and settled on the surface.

The team's work has yielded the most comprehensive record of the distribution of sulphur isotopes on Mars.

In effect, they have compiled a database of atomic fingerprints that provide a standard of comparison for sulphur-containing samples collected by NASA's Curiosity rover and future Mars missions.

This information will make it much easier for researchers to zero in on any signs of biologically produced sulphur, Farquhar said.

More information: Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars, Nature, DOI: 10.1038/nature13175