| This artist’s impression of the interior of Saturn’s moon Enceladus shows that interactions between hot water and rock occur at the floor of the subsurface ocean — the type of environment that might be friendly to life, scientists say. (NASA/JPL-Caltech) |
Excerpt from latimes.com
Scientists say they’ve discovered evidence of a watery ocean with
warm spots hiding beneath the surface of Saturn’s icy moon Enceladus.
The findings, described in the journal Nature, are the first signs of
hydrothermal activity on another world outside of Earth – and raise the
chances that Enceladus has the potential to host microbial life.
Scientists have wondered about what lies within Enceladus
at least since NASA’s Cassini spacecraft caught the moon spewing salty
water vapor out from cracks in its frozen surface. Last year, a study of
its gravitational field hinted at a 10-kilometer-thick regional ocean
around the south pole lying under an ice crust some 30 to 40 kilometers
deep.
Another
hint also emerged about a decade ago, when Cassini discovered tiny dust
particles escaping Saturn’s system that were nanometer-sized and rich
in silicon.
“It’s a peculiar thing to find particles enriched with
silicon,” said lead author Hsiang-Wen Hsu, a planetary scientist at the
University of Colorado, Boulder. In Saturn’s moons and among its rings,
water ice dominates, so these odd particles clearly stood out.
The
scientists traced these particles’ origin to Saturn’s E-ring, which
lies between the orbits of the moons Mimas and Titan and whose icy
particles are known to come from Enceladus. So Hsu and colleagues
studied the grains to understand what was going on inside the gas
giant’s frigid satellite.
Rather
than coming in a range of sizes, these particles were all uniformly
tiny – just a few nanometers across. Studying the spectra of these
grains, the scientists found that they were made of silicon dioxide, or
silica. That’s not common in space, but it’s easily found on Earth
because it’s a product of water interacting with rock.
Knowing how
silica interacts in given conditions such as temperature, salinity and
alkalinity, the scientists could work backward to determine what kind of
environment creates these unusual particles.
A scientist could do the same thing with a cup of warm coffee, Hsu said.
“You
put in the sugar and as the coffee gets cold, if you know the relation
of the solubility of sugar as a function of temperature, you will know
how hot your coffee was,” Hsu said. “And applying this to Enceladus’s
ocean, we can derive a minimum [temperature] required to form these
particles.”
The
scientists then ran experiments in the lab to determine how such silica
particles came to be. With the particles’ particular makeup and size
distribution, they could only have formed under very specific
circumstances, the study authors found, determining that the silica
particles must have formed in water that had less than 4% salinity and
that was slightly alkaline (with a pH of about 8.5 to 10.5) and at
temperatures of at least 90 degrees Celsius (roughly 190 degrees
Fahrenheit).
The heat was likely being generated in part by tidal
forces as Saturn’s gravity kneads its icy moon. (The tidal forces are
also probably what open the cracks in its surface that vent the water vapor into space.)
Somewhere
inside the icy body, there was hydrothermal activity – salty warm water
interacting with rocks. It’s the kind of environment that, on Earth, is
very friendly to life.
“It’s kind of obvious, the connection
between hydrothermal interactions and finding life,” Hsu said. “These
hydrothermal activities will provide the basic activities to sustain
life: the water, the energy source and of course the nutrients that
water can leach from the rocks.”
Enceladus, Hsu said, is now likely the “second-top object for astrobiology interest” – the first being Jupiter’s icy moon and fellow water-world, Europa.
This
activity is in all likelihood going on right now, Hsu said – over time,
these tiny grains should glom together into larger and larger
particles, and because they haven’t yet, they must have been recently
expelled from Enceladus, within the last few months or few years at
most.
Gabriel Tobie of the University of Nantes in France, who was
not involved in the research, compared the conditions that created
these silica particles to a hydrothermal field in the Atlantic Ocean
known as Lost City.
“Because it is relatively cold, Lost City has
been posited as a potential analogue of hydrothermal systems in active
icy moons. The current findings confirm this,” Tobie wrote in a
commentary on the paper. “What is more, alkaline hydrothermal vents
might have been the birthplace of the first living organisms on the
early Earth, and so the discovery of similar environments on Enceladus
opens fresh perspectives on the search for life elsewhere in the Solar
System.”
However,
Hsu pointed out, it’s not enough to have the right conditions for life –
they have to have been around for long enough that life would have a
fighting chance to emerge.
“The other factor that is also very
important is the time.… For Enceladus, we don’t know how long this
activity has been or how stable it is,” Hsu said. “And so that’s a big
uncertainty here.”
One way to get at this question? Send another mission to Enceladus, Tobie said.
“Cassini
will fly through the moon’s plume again later this year,” he wrote,
“but only future missions that can undertake improved in situ
investigations, and possibly even return samples to Earth, will be able
to confirm Enceladus’ astrobiological potential and fully reveal the
secrets of its hot springs. ”
Source Article from http://feedproxy.google.com/~r/AscensionEarth2012/~3/isbyAshTNRU/scientists-enceladus-may-have-warm.html
Scientists: Enceladus may have warm water ocean with ingredients for life
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