‘Ocean Worlds Exploration Program': new budget proposal calls for missions to Europa, Enceladus and Titan

Artist’s conception of Europa’s interior, with water rising through cracks in the surface, depositing salts similar to sea salt on Earth. The ocean below may be a habitable environment for some kind of life. Image Credit: NASA/JPL-Caltech
Artist’s conception of Europa’s interior, with water rising through cracks in the surface, depositing salts similar to sea salt on Earth. The ocean below may be a habitable environment for some kind of life. Image Credit: NASA/JPL-Caltech

The exploration of the outer Solar System has revealed a plethora of amazing worlds, the likes of which were little known or even unheard of just a decade ago. Among the most remarkable and tantalizing discoveries are the “ocean moons” such as Europa and Enceladus, which have oceans or seas of liquid water beneath their icy surfaces. Other moons like Titan, Ganymede, and Callisto may also have them, and even some asteroids. Titan also has seas and lakes of liquid methane/ethane on its surface. With all that water, these small worlds have become a primary focus in the search for possible life elsewhere in the Solar System. Now, a new NASA budget proposal wants to take that a step further and fund new missions to these watery moons.

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Enceladus’ water geysers may be ‘curtain eruptions’ according to new study

The water vapor jets on Enceladus are now thought to mostly be more like diffuse “curtains” rather than separate plumes. Image Credit: NASA/JPL-Caltech/SSI/PSI
The water vapour jets on Enceladus are now thought to mostly be more like diffuse “curtains” rather than separate plumes. Image Credit: NASA/JPL-Caltech/SSI/PSI

The water vapour geysers on Saturn’s moon Enceladus are one of the most fascinating phenomena in the Solar System; the jets spray far out into space in a dazzling display unseen anywhere else. Known to emanate from the “tiger stripe” fissures at the south pole, they were thought to be separate, distinct plumes erupting from the surface, but now scientists think that they might actually be mostly broader, more diffuse “curtains” of spray along the length of the fissures.

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Cassini finds evidence for hydrothermal activity on Saturn’s moon Enceladus

Cutaway view depicting the interior of Enceladus. Water, salts, organics, and methane make their way from the hydrothermal vents on the ocean bottom to the surface through cracks in the icy crust, erupting as geysers. Image Credit: NASA/JPL
Cutaway view depicting the interior of Enceladus. Water, salts, organics, and methane make their way from the hydrothermal vents on the ocean bottom to the surface through cracks in the icy crust, erupting as geysers. Image Credit: NASA/JPL

The deep oceans on Earth are teeming with life, despite the cold and darkness, thanks to hydrothermal vents which provide needed heat and nutrients in an otherwise rather uncomfortable environment. Now, the first evidence has been found for current hydrothermal activity elsewhere in the Solar System: on the ocean bottom of Saturn’s moon Enceladus.

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Cassini data indicates Enceladus’ ocean similar to soda lakes on Earth

The geysers of Enceladus, erupting through cracks in the ice at the south pole from a subsurface salty ocean or sea. Image Credit: NASA/JPL
The geysers of Enceladus, erupting through cracks in the ice at the south pole from a subsurface salty ocean or sea. Image Credit: NASA/JPL

Along with Jupiter’s infamous moon Europa, Saturn’s moon Enceladus is one of the most fascinating places in the Solar System, with its huge geysers of water vapour erupting from cracks in the surface at the south pole. The massive plumes are now thought to originate in a subsurface ocean or sea of salty liquid water, similar perhaps to Europa’s underground ocean. Now, new analysis is providing a more detailed look at the chemical makeup of this unique alien environment and its potential to support life.

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Waterworlds: the search for life in the outer solar system

It is thought that one or more of the icy moons of the outer solar system could support life.
Credit: NASA Planetary Photojournal

(My first article for AmericaSpace, republished here.)

Until relatively recently, it was thought that the best, or perhaps only, place to look for life elsewhere in the solar system was Mars. The other inner planets were much too hot while the outer gas and ice giants were far too cold – the chances of any kind of life being found, even microbes, was considered extremely unlikely at best.

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Exciting new ‘Enceladus Explorer’ mission proposed to search for life

Water vapour geysers erupting from Enceladus' south pole. Credit: NASA/JPL

Along with Jupiter’s moon Europa, a tiny Saturnian moon, Enceladus, has become one of the most fascinating places in the solar system and a prime target in the search for extraterrestrial life. Its outward appearance is that of a small, frozen orb, but it revealed some surprises when the Cassini spacecraft gave us our first ever close-up look at this little world – huge geysers of water vapour spewing from its south pole. The implications were thought-provoking: Enceladus, like Europa, may have an ocean of liquid water below the surface. Unlike Europa however, the water is apparently able to make it up to the surface via fissures, erupting out into space as giant plumes.

Now, a new project sponsored by the German Aerospace Center, Enceladus Explorer, was launched on February 22, 2012, in an attempt to answer the question of whether there could be life on (or rather, inside) Enceladus. The project lays the groundwork for a new, ambitious mission being proposed for some time in the future…

See Universe Today for the full article.

Enceladus and its water geysers pose again for Cassini

View of Enceladus' surface, image taken October 19, 2011. Credit: NASA/JPL-Caltech/Space Science Institute

Saturn’s tiny moon Enceladus was the centre of attention for the Cassini spacecraft again last week, with beautiful new photos being released of the moon and its water vapour geysers erupting from the south pole. Some views show surface detail on the moon, some are of the geysers themselves and there is a very nice shot of Enceladus silhouetted against Saturn and its rings in the background. There is even a dual ultraviolet stellar occultation in which two of the stars in the belt of the constellation Orion are seen shining through the plumes! Even though these are still raw, unprocessed images, they again capture the beauty of Enceladus and the Saturnian system…

See Universe Today for the full article.

A Tale of Three Moons: Is There Life in the Outer Solar System?

Until fairly recently, the search for life elsewhere in the solar system has focused primarily on Mars, as it is the most Earth-like of all the other planets in the solar system. The possibility of finding any kind of life farther out in the outer solar system was considered very unlikely at best; too cold, too little sunlight, no solid surfaces on the gas giants and no atmospheres to speak of on any of the moons apart from Titan…

See Universe Today for the full article.

(Note: this and future articles written for Universe Today are exclusive, therefore only a summary is posted here, which will link to the full article on UT).

Snow on Enceladus adds to evidence for subsurface ocean

Enceladus, a small icy moon of Saturn, is one of the most active places in the solar system, with dozens of geysers of water vapour and ice particles erupting from warmer fissures near the south pole, a big surprise when they were first discovered by the Cassini spacecraft several years ago. Since then, the debate has focused on their origin, but the latest evidence continues to indicate that the most likely explanation is that the plumes emanate from a subsurface reservoir of liquid water which somehow stays heated enough on this cold world to remain liquid.

Credit: NASA/JPL-Caltech/Space Science Institute

new study indicates that the geysers have probably been active for up to 100 million years. This estimate is based on the fact that a deep layer of snow blankets much of the moon, which forms when ice particles from the plumes settle back onto the surface. The “snow” is a very fine powder which coats the surface at an average rate of less than one thousandth of a millimetre per year. Yet in places the snow is 100 metres thick. This means it must have taken tens of millions of years to accumulate this much, and that such long-lived activity is most easily explained by a reservoir of liquid water beneath the surface.

Other evidence previously discussed also points to liquid water, notably that the plumes are composed of water vapour and ice particles with large amounts of salts mixed in, very similar in composition to salt water oceans on Earth. There are also various organic molecules in the plumes found by Cassini (which has flown through and directly sampled the material in them), and the combination of water, heat and organics have made Enceladus a new favourite spot in the search for extraterrestrial life.

It was also noted during the Division of Planetary Sciences / European Planetary Science Congress (DPS/EPSC) meeting going on now, that the mass of the plumes being primarily slower, salt-rich particles and the amount of ice particles in the plumes also both support a liquid water origin (courtesy of Emily Lakdawalla’s Twitter feed).

Cassini also just took some new photographs of the geysers which are actually like a very fine mist, but look dramatically beautiful when backlit by the sun.

This article was first published on Examiner.com.

Ocean spray a billion kilometres away

The Cassini spacecraft has found the best evidence yet that a salty ocean lies beneath the surface of Saturn’s moon Enceladus. As previously reported, Cassini had analyzed the icy particles being ejected from the water vapour geysers at the south pole in 2008 and 2009, with very interesting results, but now has found that the ones furthest away from the moon contain little salt, but the ones closer to the moon’s surface have much more salt, sodium and potassium specifically, and have a composition very similar to ocean water on Earth. The new study is in this week’s issue of the journal Nature.

Credit: NASA/JPL/Space Science Institute

To quote the article:

“There currently is no plausible way to produce a steady outflow of salt-rich grains from solid ice across all the tiger stripes other than salt water under Enceladus’s icy surface,” said Frank Postberg, a Cassini team scientist at the University of Heidelberg, Germany, and the lead author on the paper. When water freezes, the salt is squeezed out, leaving pure water ice behind. If the plumes emanated from ice, they should have very little salt in them.”

“The data suggest a layer of water between the moon’s rocky core and its icy mantle, possibly as deep as about 50 miles (80 kilometers) beneath the surface. As this water washes against the rocks, it dissolves salt compounds and rises through fractures in the overlying ice to form reserves nearer the surface. If the outermost layer cracks open, the decrease in pressure from these reserves to space causes a plume to shoot out. Roughly 400 pounds (200 kilograms) of water vapor is lost every second in the plumes, with smaller amounts being lost as ice grains. The team calculates the water reserves must have large evaporating surfaces, or they would freeze easily and stop the plumes.”

The “tiger stripes” are the long fissures that the geysers emanate from. At its closest, Saturn is just over a billion kilometres from Earth. It was previously thought almost impossible that liquid water, never mind an ocean, could exist so far from the sun. But, as theorized, between tidal stress from Saturn and inner radioactive decay, that’s exactly what is on Enceladus (and Jupiter’s moon Europa and possibly others). And what about similar moons that may exist orbiting some of the many other gas giant planets being found in other solar systems? The geysers of Enceladus would appear to literally be ocean spray, a long way from home…