This tiny little moon, 500 kilometres in diameter, has proved
that it can surprise everybody.
Water vapour plumes with organic material coming out of this tiny
little moon. Who would have thought?
I get asked whether Enceladus is my favourite moon and at the
moment it is, partly based on the observations that my team made and
the discovery that we made at Enceladus.
So the Cassini mission was the first spacecraft mission to orbit
around Saturn and its moons.
It was also the first mission to taste what was in an
extraterrestrial ocean.
The mission kept being extended and extended, and so in the end,
the mission lasted for 13 years.
The discoveries were pretty radical.
We were flabbergasted, to be frank.
I think for me, the most surprising discovery that was
made was this water vapour plume at Enceladus, which we then followed
up with discoveries about a liquid water ocean under the surface,
a heat source, organic material.
I've now given away all the secrets!
My team and I changed
the course of the mission because this was a team effort.
So we had three flybys of Enceladus and two of these flybys were quite
distant flybys. In the data that my instrument took,
so data from the magnetic field in the environment of Enceladus, we
saw some strange signatures that we weren't expecting to see.
And what those signatures were telling us was almost as if
Enceladus was a bigger obstacle, a bigger body than it looked.
We thought maybe we hadn't got the trajectory of the spacecraft back
properly, so maybe we were seeing an artefact in the data.
But the fact that we saw it on two separate flybys meant that we
said, OK, we thought we were seeing something.
So I actually traveled out to the Jet Propulsion Lab, and I was
planning to make a presentation to the project because what I wanted
to do was I wanted to persuade them that we thought we were seeing
this really strange, atmospheric signature and that it would be
really good to go close on the third flyby.
And I was really nervous because if the flyby changed that meant
all of the plans that we had made for the last six and a half years
would have to be changed, and some instruments would not take the data
that they'd planned to. But the possibility that we would discover
this water vapour atmosphere in Enceladus was exciting enough that
the majority of people decided it was worth a go.
It was extremely nerve-wracking waiting for that third flyby.
So, you know, I'd essentially put my and my team's reputation on the
line. And so I must confess the first two or three nights
before the flyby, I didn't sleep very well.
I tossed and turned a lot because if they hadn't found anything,
no one would ever have believed anything I said again.
Every once in a while, you have to be brave
and you have to say that you think you're seeing something, but
luckily they found something.
When we had that third flyby, what we found was instead of there being
an atmosphere covering the entire surface, there was simply an
outgassing of water vapour from the South Pole.
In addition to that, because we went so close, all of the other
instruments were able to take fantastic data sets as well.
And what we found is there were cracks at the South Pole through
which this water vapour was escaping.
There was an internal heat source. There was organic material.
And so that meant we had three of the four things for potential
habitability to form.
You need a heat source.
You need liquid water.
You need organic material.
And then you need those first three things to be stable enough
over a long enough period of time that something can actually happen.
So that's when there was a real focus on Enceladus for potentially
being a place where life or habitability might have been there
in the past or might be able to form in the future.
The coming together of all of the Enceladus data and the discoveries
that were made underpins what I think is one of the most important
discoveries that has been made in planetary science in the last 30
years. And that is that you don't need to look close to the sun to
find liquid water.
You can be quite far from the sun, but you can find liquid water.
It's just not on the surface, it's underneath the surface.
And so that's been almost a sea change in planetary science.
We now have a much better understanding about Enceladus and
its internal structure. So we have a global liquid water ocean
underneath the surface of Enceladus, and the surface is
made up mainly of water ice.
The biggest unanswered questions for Enceladus are, Why is there
only a water vapour plume at the South Pole?
We still don't quite understand why there's a heat source because
the fact remains that it was formed billions of years ago
because it's so small it should have cooled down.
And so we think it might be linked to its orbit around Saturn.
So if the orbit around the moon is not completely circular,
then on some parts of the orbit, it's closer to the planet than on
others. And when that happens, tidal forces keep the interior warm.
I think Enceladus will always be memorable for me because
in some ways it was my way of becoming confident in my
ability to persuade people, but also confident in my team and what
we were able to do with the data.
That's probably why it's my favourite moon.
Depending on what we discover at Ganymede, it might move slightly
down my list. For me, it was almost a coming of age for my team,
but also for the instrument.
You know, people say to me, Why do you explore planets?
And for me, we are explorers.
Humankind have always been explorers.
When we didn't know much about the Earth, people would take ships and
and go to what some people said was the edge of the Earth, and they
were scared they were going to fall off. For me, exploring planets is
part of that exploration.
It's what we do. My first view of Saturn actually was through a
telescope that my dad built.
I saw Saturn and its rings, didn't see any of the moons because
Saturn is so far away.
But we were able to see the rings clearly, and we also saw Jupiter and
some of its moons as well.
So, I never thought back when I was a child that I'd end up doing what
I do today.
I will never forget Enceladus.
In planetary science,
it will always be an important thing, and it will be an example
that people refer to in the future as well.