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…

Freelance writing

On a personal note, I am working on expanding my writing portfolio, and I am available for freelance articles focusing on space exploration, astronomy and related subjects, which I have been involved with my entire life. If you have a need for this, please contact me. Thanks!

‘Ice Queen’ Helene close-up

The Cassini spacecraft has just returned some beautiful new close-up photos of the tiny Saturnian moon Helene, a rather odd-looking little world (click on image for larger view)…

Credit: NASA/JPL-Caltech/Space Science Institute

The dust landslides (as theorized) producing the gully-like features are very prominent in this view, as is the mottled-looking terrain of smooth areas and darker areas, making the moon appear almost like a 3-D piece of abstract art.

More images are here.

Note: Helene is named after Helen of Troy, but I’m not sure where NASA’s nickname of “ice queen” came from exactly, although Helene, like some other small moons, is thought to be made mostly of rock-hard water ice.

MESSENGER update

Until now, the innermost and smallest planet, Mercury, had been relatively unexplored apart from the brief flyby by Mariner 10 in the 1970s. But the orbiting MESSENGER spacecraft is changing that, revealing new details about this little world.

The crater Degas. Credit: NASA/The Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

New images now surface at an average of 250 metres per pixel and a global base colour map at about 1.2 kilometres per pixel. The extensive volcanic plains near the north pole may be several kilometres deep. Some of the most interesting features are clusters of irregular, rimless pits which vary in size from hundreds of metres to several kilometres in size, and photographed with a resolution down to only 10 metres per pixel. They are often surrounded by some sort of higher-reflectance material.

Some of the unusual rimless pits. Credit: NASA/The Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Despite Mercury’s accurate reputation of being a searingly hot world so close to the sun, MESSENGER is also providing new data indicating that there may be water ice on the floors of craters which are permanently in shadow, which have also been observed by radar with the Arecibo Observatory on Earth. Since there is no atmosphere to speak of to distribute heat, temperatures in daylight can be hundreds of degrees, yet far below zero in the shade, similar to the Moon.

Radar image of deposits thought to be water ice. Credit: National Astronomy and Ionosphere Center, Arecibo Observatory

An additional good overview of the results so far is here.

Dawn getting closer to Vesta

After a years-long voyage since 2007, the Dawn spacecraft is now finally getting closer to the giant asteroid Vesta, which has never been seen up close until now. The newest images taken are now starting to surpass the previous best ones from the Hubble Space Telescope. Dawn will arrive at and orbit Vesta on July 16.

Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Vesta is the second largest asteroid, with an average diameter of about 520 km (320 miles). Dawn is then scheduled to leave Vesta in July 2012 and arrive at the largest asteroid, Ceres, in February 2015. Ceres and Vesta are also considered to be minor planets due to their much larger size than most other asteroids. Ceres may even have a very thin atmosphere and seasonal polar caps of water frost.

The images of Vesta will keep getting better as Dawn approaches and I will post more as they become available.