This is Enceladus,
Saturn's sixth largest moon, a tiny
world orbiting a giant planet. But don't
let its seemingly unimpressive size fool
you. When the Cassini space probe found
huge cryovcanic plumes erupting from its
south pole, this little world brought
the entire scientific community to a
standstill.
What was going on?
Flying through these icy jets got us
closer to an answer. The probe
discovered water, organic molecules, and
hints of a hidden ocean filled with
hydrothermal vents.
But in 2017, Cassini ran out of fuel. As
it dived into Saturn, it took with it
our only means of probing Enceladus,
leaving us with countless unanswered
questions. Does it have a global ocean?
What exactly is happening below the
surface? And most importantly, could it
be home to life?
A decade on, we've not yet returned to
Enceladus, but the science hasn't
stopped. The James Web Space Telescope
has turned its attention to the moon,
and researchers are still mining the
data that Cassini sent back. And
luckily, we found more answers than you
might think. I'm Alex Mccoan and you're
watching Astramm. Join me today as we
return to this surprise in the Saturn
system, explore the incredible chemical
complexity hiding below its surface, and
reveal how 10-year-old data is still
shocking us all in the search for life
beyond Earth.
At just 500 km across, Enceladus is a
tiny world. It's similar in size to the
state of Arizona.
It orbits 238,000
km from Saturn, where the sun is a mere
distant spark, and surface temperatures
average a bone chilling -2°
C. All these factors make Enceladus an
incredibly difficult target to track. It
was finally discovered by Sir William
Hershel in 1789 and to spot it required
the largest telescope the world had ever
seen. The instrument built by Hershel
and his sister Caroline was so
pioneering that its halfton mirror
required more than a year of painstaking
polishing. Yet even through this Bermoth
scope, Enceladus looked like nothing
more than an unremarkable icy rock.
Hersel's telescope was so far ahead of
its time that this remained our only
perspective of the Saturnian satellite
for nearly 200 years. It wasn't until
the 1980s when Voyager 1 and two
performed their swift liby that our
perspective shifted forever. The images
sent back didn't show the featureless
world we expected, but instead revealed
regions that were remarkably smooth and
craterfree, suggesting the moon had been
recently seismically active.
Most curiously, Enceladus was found
sitting directly in the densest part of
Saturn's E-ring, leading scientists to
suspect the moon was somehow feeding the
ring with material.
Was Enceladus alive?
The mysteries raised by the Voyager
flybys made Enceladus a high priority
target for a follow-up and directly
fueled the planning of the Cassini
Huygens mission. The Titan 4B rocket
launched Cassini in 1997 and in late
2004, 6 years after its double slingshot
maneuver around Venus, it reached Saturn
to carry on Voyager's legacy.
It was a monumental effort that has
since generated more than 4,000
scientific papers, but no discovery
caused more hype than the events of
early 2005.
During its first flybys, Cassini's
cameras caught sight of massive gizers
erupting from Enceladus into the vacuum
of space. These vents were ejecting 250
kg of water and ice every second at
speeds of over 1,000 km per hour. This
confirmed it. Enceladus had an
atmosphere and active geology.
NASA immediately shifted the mission's
course, ordering Cassini to perform a
maverick maneuver, passing just 50 km
above the surface to taste the plumes.
What was worth such a risk, you might
ask? Well, NASA were looking for signs
of extraterrestrial life.
Now, back to that radical Cassini maneuver. A major motivator of our
exploration of space is the hope that
we're not alone. To define life, NASA
looks for a self- sustaining chemical
system capable of Darwinian evolution.
But what does that mean when we are
searching on Enceladus? Well, there are
four boxes we need to check. liquid
water, energy, chemicals, and time.
First up, liquid water, the solvent of
life. The question here isn't whether
Enceladus has it. That's abundantly
clear, but rather we need to ask, how
much water is there, and where is it
coming from? Cassini's initial photos
and infrared images from 2006 showed
significant heat at the South Pole.
This incredible photo shows the famous
tiger stripes, long fishissures in the
icy crust, hinting at the activity
below. And clearly some form of a liquid
ocean exists here, potentially with
hydrothermal activity that powers the
huge ice plumes. For years, scientists
believed this ocean was small and lens
shaped. However, by meticulously
tracking surface features over 7 years,
they noticed the moon librates or
wobbles a lot more than would be
possible with just a small polar ocean.
This finding led to an astonishing
realization. The core isn't rigidly
connected to the surface.
We are now confident that the ocean
covers the rocky core across its entire
surface. In 2025, there was another
breakthrough. Scientists from the
University of Oxford, Southwest Research
Institute, and the Planetary Science
Institute looked back through the
Cassini observations of the North Pole
from its winter in 2005 and summer in
2015. They found that not only was heat
escaping at the South Pole, but also at
the North Pole, it was 7° warmer than
they expected. This result tells us that
Enceladus is generating a lot more
internal heat than we thought and
suggests the ocean may have been there
for a while. But this far from the sun,
it is bitterly cold. As I mentioned, the
surface temperature of Enceladus is -20°
C. There's no way water should be
liquid. So, next on the list for
scientists to check out was energy.
Where was the heat coming from? If
Enceladus generated heat by radioactive
decay in its core like Earth does, the
energy produced would only be 1% of what
Cassini was witnessing. So in 2017, a
team led by Gail Shabé proposed a
solution. Enceladus is tidily locked to
Saturn, meaning the moon only ever shows
one face to the planet. This distorts
Enceladus, which creates heat inside the
moon through internal friction and
powers geological activity. But it's not
enough to just generate and radiate the
heat. It needs to be physically
transported from the core to the ocean
above. How? Well, incredibly, it seems
that water beuses the silicut mineral
core where it is heated, causing it to
rise in focus plumes that pepper the
seafloor around the South Pole. In 2022,
a study led by Wan Khan found further
proof of these events. Based on
Cassini's data, they created models of
Enceladus's icy surface to try and work
out the salinity of the ocean. They
found that it's just a little less salty
than we find here on Earth. And that
means that there must be or have been
water rock reactions, or in other words,
vents at some point.
Hydrothermal vents are credited by
scientists as powering the origin of
life on Earth. That these vents may also
exist on a small moon around a gas giant
is an electrifying discovery because
they give us the third requirement for
life, chemicals.
Cassini was equipped with a mass
spectrometer, an instrument that can
identify individual molecules by the
mass of their ions. On its flybys, it
detected hydrogen believed to be a fuel
source for early life and complicated
hydrocarbons containing oxygen, carbon,
and nitrogen. But scientists racing to
process the huge volume and richness of
data couldn't keep up. Before they could
get through it all, the Cassini mission
came to an end. And on the 15th of
September 2017, it was sent hurtling
towards Saturn and was vaporized by the
planet's atmosphere in a
self-destructive maneuver designed to
protect potential habitable life on
Enceladus and Titan from contamination
by Earthborn microbes.
Though Cassini's mission had been
completed, ours had not. An analysis in
2018 had confirmed the existence of
ringshaped organic molecules and simple
oxygen containing molecules, indicating
some limited chemistry was occurring.
Another huge boost to the search for
life came in 2022 when the last element
crucial to life was observed in the
data, phosphorus.
With its discovery, we now had all six
main elements believed to be necessary
for life. carbon, hydrogen, nitrogen,
oxygen, phosphorus, and sulfur, which
scientists know by the acronym Chinups.
For a while, this felt like the end of
the story. But it turns out this
particular book had a few more chapters
to go.
When scientists first saw the mass spec
data from Cassini, they weren't
confident in what they were looking at.
It turns out that the spectra of a
carefully prepared sample analyzed while
stationary in a lab looks somewhat
different to the one obtained by
crashing the detector into a ejector at
64,000 kmh in space.
A mass spectrum analyzer works by
ionizing and breaking a molecule apart
at high energy. How the molecule breaks
apart matters. A molecule's fingerprint
can look different depending on how it
was fragmented. In the same way that a
watermelon prepared with a knife looks
different from one prepared with a
blender. By understanding the typical
pattern of how an object breaks under
certain conditions, we can be more
confident of what it used to be.
Improved analytical tools helped the
team led by Nosa Kavajar from the
Institute of Space Systems in Stogart do
exactly that. After more than a decade
of studying the plume flybys, Kawaja's
team published their results last year
using samples that were collected when
Cassini passed just 20 km from the
moon's surface. Unlike others the probe
collected, they were just minutes old
and therefore unchanged by ionizing
radiation from the sun like other
particles in the E-ring. These samples
were a pristine example of what's in the
oceans of Enceladus. In the most extreme
examples, they found molecules more
closely related to life than ever
before. carbon dioxide, carbonri alkanes
and alkenes, cyclic esters and ethers,
ethals and other nitrogen and oxygen
bearing compounds. In other words,
complex chemistry potentially powered by
hydrothermal vents. These molecules are
the Lego blocks of chemistry. More
functional groups allow for more complex
reactions. In a lab, these can become so
complex that they even demonstrate
Darwinian evolution. And once you have
evolution, there's just one last
requirement.
Time.
What we need to know is how stable and
frequent is this geothermal activity?
Would life have had enough time to
emerge on Enceladus?
Although Cassini was at Saturn for 13
years, that was of course too short a
time to be conclusive. Enter the James
Webb Space Telescope.
A team led by Dr. Heronimo Villian Noeva
used 10 hours of the James Webb's time
to check in on Enceladus. And what they
saw was shocking. The moon had an even
more enormous plume erupting from its
south pole, expanding to 20 times the
size of the moon itself. That is
significantly larger than what Cassini
saw. These observations widened the
known window of Enceladus' activity. And
they solved another massive mystery.
Where does Saturn's atmospheric water
come from? The images show that
Enceladus feeds a large Taurus of ice
particles around Saturn, making it the
only moon in the solar system that
affects the atmospheric chemistry of its
host planet.
But these water ice particles also have
another impact on the planet. As they
travel through the Saturn system,
they're stripped of electrons, becoming
ionized. This then creates an
electrically charged plasma, which
scientists have recently discovered
interacts with the planet's magnetic
field. Plasma waves 504,000
km long, that's 1,000 times the moon's
diameter, known as the alphen wings,
stream from the moon. The main ones go
from Enceladus to the planet, but others
are reflected back, creating an
intriguing latis of plasma around
Saturn. We still don't fully understand
them, but they're a surprising
consequence of Enceladus's great gizers.
But how long will this activity last?
Within the last year, decade old data
from the Cassini composite infrared
spectrometer was compared to models of
Enceladus's surface temperature. The
team comprising Georgina Miles and Carly
Howitt were able to show that the total
thermal output from the surface is very
well matched with the predicted heat
generation in the core. This suggests
the moon's current ocean epoch will be
longived and that it is exactly what
life needs to emerge.
It is incredible how much more has been
learned simply from reanalyzing old
Cassini data with new techniques. And
it's not just the professionals who are
making discoveries. In 2017, amateur
astronomer Ted Strike looked back at old
Voyager images of Enceladus and found a
feature that could have changed the
course of the original Cassini mission,
a water plume. Can you spot it? If we
had known about it when the mission was
in planning, how different might the
design of Cassini been? Well, whatever
changes scientists and engineers might
have made, they now have a chance to be
realized as new missions are being
planned to continue the work of Cassini.
The European Space Agency is racing
forward with a mission set to launch in
2042 to arrive at Saturn in 203 with a
potential landing on Enceladus in 208.
We already know Enceladus has all the
conditions to kickstart life. So, it's
exciting to think what will we be able
to find when we look below the ice.
Fortunately, we won't have to wait quite
that long to get some answers on life on
icy moons generally. Another issa
mission called Juice or Jupiter Icy
Moons Explorer is already on its way and
expected to arrive at Jupiter in 2031 to
study Kalisto, Europa, and Ganymede. Its
mission purpose is to investigate the
emergence of habitable worlds around gas
giants. Two other proposed missions will
explore Saturn's moons in new ways. The
Dragonfly mission to Titan will take
advantage of the thick nitrogen
atmosphere and use a drone for the first
time on a natural satellite.
Outside of the national space agencies,
a privately funded mission called
Breakthrough Enceladus is also planned,
though currently this project appears to
be dormant.
But the mission I'm most excited about
is the Enceladus Explorer, a project
funded by the German Aerospace Center
that proposes to send a nuclear ice
mole. Yes, you heard that correctly. To
melt its way deep into the crust and
expose untouched niches within the ice
to search for life. If any of these even
hint that protolife processes are active
on an object outside the usual habitable
zone, we will have opened up a whole new
realm of possible places life could take
hold across the galaxy. Maybe life isn't
rare after all.
I'm always reminded of a fantastic line
from Jeremy England. You start with a
random clump of atoms and if you shine a
light on it for long enough, it should
not be so surprising that you get a
plant.
Perhaps scientists didn't see those
plumes on the original Voyager images
because they simply weren't expecting to
see them. But now that we know what
we're looking for, there is no doubt
more discoveries are on the way. There
is also almost certainly yet more to
find within Cassini's data. even now, a
decade after its mission ended in
spectacular style. And I am as excited
now as I was in 2004 when the probe
first reached Saturn and its moons.