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Ocean Worlds Beyond Earth

We’re incredibly lucky to live on a planet
drenched in water, nestled in a perfect distance from our sun and wrapped with
magnetic fields keeping our atmosphere intact against harsh radiation and space
weather.

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We know from recent research that life can
persist in the cruelest of environments here on Earth, which gives us hope to
finding life thriving on other worlds. While we have yet to find life outside
of Earth, we are optimistic about the possibilities, especially on other ocean
worlds right here in our solar system.  

So…What’s the News?!

Two of our veteran missions are providing
tantalizing new details about icy, ocean-bearing moons of Jupiter and Saturn,
further enhancing the scientific interest of these and other “ocean worlds” in
our solar system and beyond!

Cassini
scientists announce that a form of energy for life appears to exist in Saturn’s
moon Enceladus, and Hubble
researchers report additional evidence of plumes erupting from Jupiter’s moon
Europa.

The Two Missions: Cassini and Hubble

Cassini

Our Cassini
spacecraft
has found that hydrothermal vents in the ocean of Saturn’s icy moon Enceladus
are producing hydrogen gas, which could potentially provide a chemical energy
source for life.

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Cassini discovered that this little moon of
Saturn was active in 2005. The discovery that Enceladus has jets of gas and icy
particles coming out of its south polar region surprised the world. Later we
determined that plumes of material are coming from a global ocean under the icy
crust, through large cracks known as “tiger stripes.” 

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We have more evidence now – this time sampled
straight from the plume itself – of hydrothermal activity, and we now know the
water is chemically interacting with the rock beneath the ocean and producing
the kind of chemistry that could be used by microbes IF they happened to be
there.

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This is the culmination of 12 years of
investigations by Cassini and a capstone finding for the mission. We now know Enceladus
has nearly all the ingredients needed for life as we know it.

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The Cassini spacecraft made its deepest dive
through the plume on Oct. 28, 2015. From previous flybys, Cassini determined
that nearly 98% of the gas in the plume is water and the rest is a mixture of
other molecules, including carbon dioxide, methane and ammonia. 

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Cassini’s other
instruments provided evidence of hydrothermal activity in the ocean. What we
really wanted to know was…Is there hydrogen being produced that microbes could
use to make energy? And that’s exactly what we found!

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To be clear…we haven’t discovered microbes at
Enceladus, but vents of this type at Earth host these kinds of life. We’re
cautiously excited at the prospect that there might be something like this at
Enceladus too!

Hubble

The Hubble Space
Telescope
has also been studying another ocean world in our solar system:
Europa!

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Europa is one of the four major moons of
Jupiter, about the size of our own moon but very different in appearance. It’s
a cold, icy world with a relatively smooth, bright surface crisscrossed with
dark cracks and patches of reddish material.

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What makes Europa interesting is that it’s believed
to have a global ocean
, underneath a thick crust of ice. In fact, it’s got
about twice as much ocean as planet Earth!

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In 2014, we detected evidence of intermittent
water plumes on the surface of Europa, which is interesting because they may
provide us with easier access to subsurface liquid water without having to
drill through miles of ice.

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And now, in 2016, we’ve found one particular
plume candidate that appears to be at the same location that it
was seen in 2014. 

This is exciting because if we can establish that a
particular feature does repeat, then it is much more likely to be real and we
can attempt to study and understand the processes that cause it to turn on or
off. 

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This plume also happens to coincide with an
area where Europa is unusually warm as compared to the surrounding terrain. The
plume candidates are about 30 to 60 miles (50 to 100 kilometers) in height and are well-positioned for
observation, being in a relatively equatorial and well-determined location.

What Does All This Mean and What’s Next?

Hubble and Cassini are inherently different
missions, but their complementary scientific discoveries, along with the synergy
between our current and planned missions, will help us in finding out whether
we are alone in the universe. 

Hubble will continue to observe Europa. If
you’re wondering how we might be able to get more information on the Europa
plume, the upcoming Europa Clipper mission
will be carrying
suite of 9 instruments to investigate whether the mysterious icy moon could harbor conditions favorable for life. Europa Clipper is slated to launch in the 2020s.

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This future mission will be able to study the
surface of Europa in great detail and assess the habitability of this moon.
Whether there’s life there or not is a question for this future mission to
discover!

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Source: NASA

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Ocean Worlds Beyond Earth

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