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…

Enceladus even hotter than thought

The mysteries of Saturn’s moon Enceladus just get more puzzling… it’s been known for a while now that the water vapour/ice geysers at the south pole emanate from fissures where heat is continuously leaking, more than was thought possible for such a tiny world. Now, new data from the Cassini spacecraft shows that much more heat than that even is coming out of Enceladus’ interior.

Credit: NASA/JPL/Space Science Institute
Credit: NASA/JPL/Space Science Institute

The expected heat energy output from tidal heating, based on a 2007 study, was about 1.1 gigawatts (averaged out over time). Plus maybe another 0.3 gigawatts from natural radioactive heating. But the new results indicate an energy output of 15.8 gigawatts, about 2.6 times the energy from all of the hotsprings in Yellowstone, or 20 coal-fueled power stations. For a tiny, icy body like Enceladus, that’s amazing, and also makes it even more likely that the geysers originate from a subsurface sea or ocean. A salty one at that, as salts have already been found in the vapour/ice plumes, as well as organic molecules. What else might be lurking below?

See also the Enceladus image gallery for more great photos.

Miscellaneous wrap-up

As noted earlier, I missed posting more the last few weeks due to being sick, but here is a condensed summary of some of the other recent interesting updates as we come to the end of 2010…

Does Pluto, of all places, have a subsurface ocean? This new report says maybe; Cassini has found new evidence for an ice volcano on Titan; the building blocks of life could possibly form on Titan’s surface more easily than thought if there is any liquid water temporarily on the surface from ice volcano eruptions (or comet impacts); there’s a new theory on how Iapetus may have obtained its odd equatorial ridge; the “arsenic life” discovery continues to be criticized by some other scientists (see also here) while the scientists involved have responded and rebutted those claims (see also here); the Spitzer space telescope has found the first known carbon-rich exoplanet; a fourth large exoplanet has been photographed orbiting a star 129 light-years from Earth; another smaller exoplanet, a “super-Earth” was found to have an atmosphere with either high clouds or hot steam; a new study says that the entire Tharsis Rise on Mars should be named the largest known volcano in the solar system instead of the current Olympus Mons (one of four volcanoes that are part of Tharsis Rise); the warm fissures on Enceladus, the source of its water-ice geysers, were seen up-close by Cassini again; there may be another Jupiter-sized planet hiding out in the outer solar system; and finally, the current known exoplanet count is now 516 (and the hope was for at least 500 by the end of this month)!

Highlighted by, among other things, the next exoplanet update from Kepler in February and the launch of Curiosity, the next bigger and better Mars rover, in November, 2011 should also be an interesting year…

A “Perrier ocean” on Enceladus?

A new study suggests that the water-ice geysers on Saturn’s moon Enceladus originate from a bubbly, salty subsurface sea or ocean, a variation of previous theories.

New image of the plumes, released October 1, 2010. Credit: NASA/JPL/Space Science Institute

From the article:

“Matson and his colleagues came up with a computer model that accommodates much of what is known about the geysers of Enceladus. Their findings support the supposition that a salty sea flows under the moon’s surface.

This ocean has gases dissolved in it, the theory goes. As the seawater flows up to and through the tiger stripe fissures, its pressure drops and the gases bubble up, Matson said — making the ocean fizzy, like Perrier. The relatively warm water and expanding gas feed the jets.

When the bubbles pop, they throw off a fine spray that contains salt and other materials, which Cassini spotted in Enceladus’ plumes. Then the seawater, having dumped much of its warmth on the moon’s surface ice, cools and sinks back through cracks, rejoining the ocean and its heat-transferring circulation system.”

Perrier, anyone?


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