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

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