Amazing Moons   
       
   March 11, 2016: When the Space Age began more than 50 years ago, explorers   
   were eager to visit the planets of the solar system.  As the years have   
   passed, however, astronomers have realized that the moons of the solar system   
   may be even more interesting.   
       
   Many of these moons are `water worlds' - and planetary scientists, like golden   
   retrievers, always follow the water.   
       
   "On Earth, where there is water, there is life," says Brian Day of NASA's   
   Solar System Exploration Research Virtual Institute. "It doesn't matter if   
   it's boiling hot like the bubbling acid hot-springs in Yellowstone National   
   Park or frigid like the waters of the Arctic."   
       
   https://www.youtube.com/watch?v=CQjZf2bW9XQ   
       
   Consider Enceladus, a tiny moon floating just outside Saturn's rings. This   
   little wonderland features a vast underground ocean that could be friendly to   
   microbial life. That ocean is capped by a thick crust of ice. Yet, NASA's   
   Cassini spacecraft found Enceladus busily puffing plumes of water vapor, icy   
   particles, and organic compounds out through fissures in its frozen outer   
   shell. Cassini has actually flown through these plumes a few times, sniffing   
   out their composition.   
       
   Day says, "The exciting results from Cassini have researchers designing   
   possible future missions that would provide more detailed analyses of   
   Enceladus' water and look for potential signatures of life."   
       
   Titan, another of Saturn's moons, is shrouded in a thick atmosphere of   
   nitrogen and methane. There is evidence that Titan, like Enceladus, has a sea   
   of water beneath its icy shell. But Titan's frigid surface is mosaicked with   
   lakes of liquid methane and ethane.   
       
   Day notes, "It's the only body in the solar system other than Earth with   
   substantial liquid on its surface."   
       
   The seas of Titan intrigue astrobiologists.  Here on Earth, our seas are   
   teeming with life-and indeed the seas may be where life began. What kind of   
   life might arise in the alien seas of Titan? The exotic environment of   
   hydrocarbon seas could teach astrobiologists a lot about the basic chemistry   
   critical to the formation of life.   
       
   More water worlds with icy shells are found at Jupiter. Europa, Ganymede, and   
   perhaps Callisto also show strong evidence of liquid water oceans beneath   
   their global ice crusts. Day would most like to `dive in' at Europa.   
       
   "This is a big world -much bigger than Enceladus and even bigger than any of   
   the `dwarf planets'. Europa's ocean is a significant body of water with   
   amazing potential for life."   
       
   In fact Europa has twice as much liquid water as Earth, and like the water of   
   Enceladus, it might be accessible.   
       
   "There is some evidence that Europa may have periodic eruptions of plumes of   
   water, similar to those seen on Enceladus. We've even seen apparent icebergs   
   on the surface that are tipped up as if sitting in slush. All of these provide   
   us with tantalizing clues of what lies beneath - an ocean of liquid water."   
       
   Meanwhile, orbiting Jupiter not far from Europa, is a completely different   
   kind of satellite:   
       
   "Io," says Day, "is the most volcanically active body in our solar system."   
       
   Io gets its fiery warmth from tidal heating-that is, a back and forth   
   stretching of the moon's interior caused by Jupiter's intense gravity.   
       
   "Each moon is stretched and pulled differently, causing varying rates of tidal   
   heating. Orbiting more closely to Jupiter than the other Galilean moons, Io is   
   stretched the most -hence its volcanism. Europa, next closest to Jupiter, is   
   stretched less, followed in order by Ganymede and Callisto."   
       
   Day continues, saying "Tidal heating is a source of energy that can melt ice   
   and expand the potential for life. It creates a `habitable zone' among the   
   moons of Jupiter, with Europa sitting squarely in the middle."   
       
   Planets are exciting, but there's an even greater number of amazing moons in   
   the solar system.   
       
   Says Day: "The lure is irresistible, and the potential is amazing. It's time   
   for us to go!"   
       
   For more news about amazing moons-and their planets-stay tuned to   
   science.nasa.gov.   
       
       
   Regards,   
       
   Roger   
      
   --- DB 3.99 + Windows 10   
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