Saturn moon pops its cork

The crescent moon greeted sky watchers this morning up before sunrise. Credit: John Chumack

Darkness is slipping away at the rate of almost 3 minutes a day as January gives way to the month of candy hearts. That’s how an astronomer might look at the progress of the seasons. The flip side is that the sun is up longer by the same amount. I found a quiet, windless spot on a snowy ridge yesterday, faced the sun and closed my eyes. Seconds later I could feel a gentle warmth on my cheeks and legs. Though the night hours may be dwindling, this daylight thing ain’t so bad.

Ice covers the western end of Lake Superior as far as the eye can this weekend. Photo: Bob King

Even though the sun rises earlier and sets later than a month ago, ice doesn’t form and stick at the western end of Lake Superior in Duluth until mid-winter. It takes weeks of cold days and nights for that to happen. This weekend we had some decent ice on the lake. Nothing you could walk on yet, but it spanned the distance to the Wisconsin shore. The crazed, cracked and bumpy texture of the ice bore a strong resemblance to one of my favorite ice worlds, Saturn’s moon Enceladus.

Enceladus' tiger stripes are shown in false-color blue (at left) in this photo of the moon taken by the Cassini probe. Click to enlarge. Credit: NASA/JPL/ESA

Enceladus (en-CELL-uh-duss) has been in the spotlight in recent years with the discovery by the Cassini probe of water vapor, icy particles and organic compounds venting into space from long fissures nicknamed “tiger stripes”near the south pole. The source of the moon’s many geysers is believed to be an ocean deep beneath the surface. As Enceladus orbits Saturn, it’s alternatively stretched and compressed by the planet’s powerful gravity, generating internal heat that partially melts the moon’s interior. Liquid water is the result.

Geysers of ice particles and organic compounds spew from the tiger stripes or long cracks in the moon's crust. Click to enlarge. Credit: NASA/JPL/SSI

But how does the water manage to find its way through tens of miles of crust to erupt as jets? Last week, Dennis Matson of NASA’s Jet Propulsion Laboratory and colleagues proposed that gases dissolved in the water form bubbles, making it fizzy like a bottle of sparkling water or a soft drink. And if you shake a bottle of soda and then pop off the top, you know what happens.

Bubbles of carbon dioxide that create the fizz in a glass of Coca-Cola

Since the density of bubbly water is less than that of ice, the sparkly stuff rises through the ice and collects in chambers near the surface. When the pressure peaks, the seltzer mix blasts through holes in the surface just like that shaken can of soda. Would that an icy Lake Superior could be so effervescent.

Since we know that Enceladus has salt water (like Earth’s oceans) and organic compounds beneath its crust, it makes you wonder whether it might be suitable for the evolution of life. I’m going to put it on my list of worlds – along with Mars, Europa and Titan – as places where we might find a little company some day.

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