This is Geology Bytes with Oliver Strimple.
The most volcanically active body in the solar system is IO,
the innermost of Jupiter's Galilean moons.
Since the 1970s, Jupiter and its moons have been visited by a
number of space probes, including Pioneer, Voyager,
Galileo and Juno. Each time one of these probes
reached IO, and even between successive orbits of a
particular probe, IO surface had changed.
In December 2023 and February 2024, Juno flew by IO at a
distance of 1500 kilometres, seeing, among other things, twin
erupting plumes and lava lakes. What drives this intense
volcanism, and what can Juno and its predecessors tell us about
the structure of IO and how it interacts with Jupiter?
Scott Bolton has a prolific research career that focuses on
Jupiter and Saturn and the formation and evolution of the
solar system. He has LED a number of science
investigations on the Cassini, Galileo, Voyager and Magellan
missions and is the principal investigator of the Juno
mission. He's director of the space
sciences department at Southwest Research Institute in San
Antonio, TX Scott Bolton, welcome to GEOLOGY Bytes.
Thanks for having me, happy to be here.
Let's start with an overview of the Jovian system.
Jupiter is the largest of all the planets in our solar system,
and therefore a lot of scientists believe it must have
formed first. Not only is it the largest
planet, it's spinning around in 10 hours.
So you have this planet that's 10 times the size of the Earth.
1000 Earths fit inside of Jupiter and yet it's spinning
faster than the Earth is. So it's it's moving around very,
very quickly. And then it has the four
Galilean moons that were discovered by Galileo, the
astronomer back in Italian Renaissance when he pointed the
first telescope up there. And the IO is one of those.
And then you have Europa, Ganymede and Callisto, and
they're moving around at different rates.
IO goes around in a little less than a couple days.
And the magnetosphere of Jupiter, which comes out of the
magnetic field of the planet, come out of the poles.
It's spinning very, very fast. It has a collection of charged
particles and that is whipping around, banging into these moons
because it's tied to Jupiter's spin rate.
So it moves around in 10 hours, all of these charged particles.
So they bang in and sputter these moons and knock off
particles. Juno is the latest space probe
to have approached Jupiter. Could you give us a summary of
the Juno mission and how it compares with the prior missions
that have reached Jupiter? Juno is somewhat unique for two
reasons. One is it goes over the poles of
Jupiter. Previously, the spacecraft have
visited around the equator. And the other thing that's new
about Juno is we go very, very close to Jupiter.
We're basically scraping just over the atmosphere as we fly
over. And so we're getting a really
close view of Jupiter and we're getting this global view.
We basically can map the planet. Each orbit comes down over a
different longitude. Voyager and Pioneer flew by, and
Cassini even flew by on its way out to Saturn.
And we got a view from the equator not that close to
Jupiter. And Galileo orbited around
Jupiter, but not as close as Juno and also confined to the
Equatorial regions. When Juno first arrived at the
Jovian system, you placed it in a 53 day highly eccentric orbit,
coming as close as you said, really scraping the top 5000
kilometres above the top of Jupiter's atmosphere.
How did you then change the orbit to get it close to IO?
Actually, Jupiter did that work for us.
We were in an elliptical orbit. So when you get close to
Jupiter, that's called Pera Jove, and when you're far away,
it's called Apojov. And our Pera Jove originally was
near the equator of Jupiter, and we were going over the poles.
And Jupiter's gravity field is asymmetric, and it kind of
twists the orbit of Juno and so that the aperage of moves more
and more north with each orbit, almost 1° per orbit.
And as we do that, when we're coming in toward the North Pole
starts getting closer and closer to the planet.
And as that moves closer to the planet, first you'll encounter
Ganymede, then you get to Europa, and finally IO.
And it's basically the orbit, what they call the line of
absides that's being twisted around.
And so we actually didn't have enough propellant to do do that.
We're just mere mortals. But Jupiter, of course, with its
giant gravity field, really controls the orbit.
So as I said, you got as close as 1500 kilometers from the
surface of IO. What instruments did you use to
study it? We have a visible camera, we
have an infrared camera and spectrometer.
We also have a full set of fields and particles that look
at the magnetosphere. So we have charged particle
instruments like for plasma, energetic particles, plasma
waves and radio emission. We have a microwave radiometer
that we basically invented to look into Jupiter's atmosphere
and to measure how much water and how the dynamics of the
atmosphere work below the clouds.
And we use that to look into the surface of IO.
And we also have magnetometers, and we also have the gravity
science, which looks at the interior structure and measures
the gravity field. And we have an ultraviolet
instrument. You have a microwave instrument.
Are we looking at black body emissions or absorptions or
reflections? How does that work to see the
atmosphere and even below the surface?
You see all of those that you just mentioned, you
predominantly see black body emissions.
So when you look at Jupiter, you have different wavelengths.
We have 6 channels and the short wavelengths or high frequency
look at the top of the atmosphere and the longer
wavelengths can see in and how far into the atmosphere is
driven by the opacity of the atmosphere, which is driven by
ammonia and water. Now when you look at IO with
that, we weren't sure what we were going to see because no
instrument like this has ever been used to really look at lava
and rocky things like that. We actually think we're seeing
into the lava a little bit because we see at the longest
wavelength channels that the temperature is going up.
That means that maybe you're seeing in where it's warmer.
But of course, even though there's tons of volcanoes all
over, it's not completely covered with volcanoes.
So it's mixed with rock and sulfur dioxide ices and things
like that. So it's a mixture of whatever we
see. We're still trying to figure out
exactly how to interpret it. Just fascinating.
To follow up on a point you made, do microwaves actually
penetrate the lava? Can you actually see a little
bit below the surface? We're not sure we think so.
We think that's what we're seeing, but we have no
calibration of this type of measurement because there's no
experience taking an instrument like this and looking at rock
and lava very much. I think that we probably are
seeing into the lava, but we definitely see the temperature
going up, which means that you're probably seeing in to the
surface where it's warmer. You mentioned that Juno's
trajectory took us for the first time over the poles of Jupiter
rather than the equator, and I wonder if its trajectory also
gave us a view of parts of IO's surface that had not been
visible to us before, and if so, whether you were able to map a
distribution of the volcanism according to the latitude on IO.
Yes, in fact we did. At the orbits approaching the
first fly by, which was in the end of December this last year,
we got the first real views of IO's North Pole, and so we made
a map of the volcanoes around the North Pole.
In the next few orbits, we'll get the first views of the South
Pole, and so we're making maps of how the volcanoes are
distributed at both poles and, of course, around the equator.
I know it's early days yet as far as receiving all the data
and processing it and so on, but so far, what kind of volcanic
activity have we seen in the latest Juno imagery of IO?
IO must be an amazing place to visit.
It's covered with volcanoes that are going off all the time.
And if you go to the poles, there's still volcanoes
everywhere. So if you were a hiker and you
were lucky enough to land on IO and you had the equipment or
some sort of natural way to survive this because it must be
really smelly there, like like Yellowstone.
And no matter where you were, you would have a view of many
volcanoes. And we also saw these incredible
mountains because we got some imagery along the Terminator.
And you can see these mountains are also all over IO that are
coupled to the volcanoes, but they're not necessarily a
volcanic. It has its own capability to
make mountains. And some of them are quite
sharp. They look like cliffs.
It's just an amazing place. Giant lava lakes.
Some of these are reflecting with specular reflections.
So at least the lava lakes must have a very, very smooth
surface. In fact, most of IO must be
relatively smooth. We compare it to Europa and
Ganymede, which we flew by years earlier, and that surface is
much more rough. The ice is rough and the
reflections is diffuse scattering, whereas in IO it's
specular, almost like it's glass.
So the frozen surface of the lava, you're saying that's shiny
on Earth? Of course it gets very matte
when we have cooled lava. It might be smooth, more like
Obsidian. If you look sometimes near
Earth's volcanic regions, you'd find Obsidian, which is a very
smooth kind of glass. So whatever's forming there
might be relatively pure and very smooth.
And then a lot of lakes are cooling.
Get a crust over them and then where the lava is coming up
might make a ring around the lake.
And sometimes there's protrusions out of that which
represent natural terrain, elevation changes, the almost
islands like. And then of course you have the
volcano itself. Sometimes we see some of that.
If you go to Hawaii or Iceland right now, you'll see this
bubbling ring of lava and there's a cooled off lake and
the material can get quite smooth.
I don't think it's liquid because it's very cold on the
surface of Isles, so the lava must be cooling very very
quickly. So you said it would be smelly
on the surface of IO. I presume you're referring to
sulphur compounds like hydrogen sulphide or sulphur dioxide.
But IO's very colourful surface has been likened to that of a
well stocked pizza. So do we know what generates all
those many Reds, yellows and the dark greens and greys and
blacks? Sulphur compounds are certainly
associated with the volcanoes as they erupt, and those are
predominantly the thing that causing the yellows and the
Reds. Now when the sulfur gas comes
out of a volcano on IO, it instantly freezes, so it turns
into snow and it's probably colored snow or dirty snow.
So you get the yellow reddish gook that's being laid around.
And the molten lava, as soon as it comes out, also starts
cooling. So when that cools off, they
produce a lot of the Grays and black.
What drives all this intense volcanism on IO and makes it the
most volcanically active body in the solar system?
Iowa's volcanic activity is really driven by Jupiter.
It's tidal forces. So the same thing that raises
the ocean here on Earth. Our moon pulls and changes our
tides. Jupiter is doing that on IO.
It's relentlessly squeezing and literally torturing this poor
moon as it orbits Jupiter. It's getting squeezed.
The gravity field is so strong, it's basically changing its
shape and it feels a stronger gravity on one side versus the
other, and that is churning inside and producing all of the
volcanic activity. Do we know anything about the
mechanism by which this heating leads to the many volcanoes that
pepper IO surface? To that, you have to look inside
of IO. And the question is, is whether
there's a global magma ocean or pockets of lava that just
produce local volcanoes. In other words, if I go down
deep into IO, is there a layer that's all lava?
And in fact, we chose to do 2 flybys in order to get the
gravity field very, very precisely to distinguish a
global magma ocean from one that is not global.
I think that in the next few months we will probably resolve
that question and put very good constraints on how IO works
inside and how it produces all of the volcanoes that we see.
We see volcanism on other bodies apart from the Earth, such as
our own moon. So not all volcanism is caused
by tidal heating then? Not all of it.
Tidal forces are much smaller here because the moon can only
do so much to us. Venus is also volcanic.
Mars you can see all the volcanoes.
So tidal forces play a role. Some of them have small moons
going around them. Or in case of Venus, it's closer
to the sun so it gets some tidal forces, but a lot of it is
geothermal as well. There's material deep down in
the planet that's keeping it warm.
Radioactive material that rayogenic heating.
People see it on Enceladus. We see crowd vents where water
is spewing out of the ice, so something cracks the ice.
People think that maybe Europa that might have blooms of water
coming out of it, the ice might be cracking as well.
It must be feeling some tidal forces from Jupiter as well,
even though it's further away than IO.
IO is the one that's really getting tortured because it's
really close. Juno has a magnetometer on
board, you said. How does IO affect Jupiter's
magnetic field, and what can we learn from that interaction?
Juno has a very, very sensitive magnetometer.
It's very powerful tool to investigate the interior of
Jupiter and actually see how the magnetic fields are produced and
map out the magnetic field of Jupiter.
Now, Jupiter's magnetic field is enormous.
In fact, it's the largest structure in the solar system.
It makes what's called a magnetosphere, which is filled
with charged particles. So the magnetometers on Juno
were designed to measure Jupiter's magnetic field and map
it. IO's impact on Jupiter's
magnetic field and magnetosphere is the fact that it's filling
the space with charged particles, material that comes
out of the volcanoes. It gets ionized through sunlight
or collisions and then starts whipping around and becomes part
of Jupiter's magnetosphere. That also feeds the Aurora.
So when they get caught up on these magnetic field lines, it's
almost like an umbilical cord between IO and Jupiter.
There's a spot in Jupiter's Aurora that actually tells you
where IO is and connecting Jupiter width IO through its
magnetic field. IO is so powerful in the fact
that it's distributing all of these charged particles from the
volcano that there's a ring around Jupiter that's called the
IO Taurus and it's filled with charged particles.
And we've known about this for a long time.
A previous missions have studied this.
You can study this from some telescopes, from the Earth even.
And this torus of charged particles around IO is very,
very high in radiation. It's very hazardous place to go
for spacecraft. And that Taurus also makes a
little bit of Aurora. So when you look at the Aurora
of Jupiter, you can see sort of a tail coming out of IO that's
coming from this Taurus ringing around.
And you can also see this spot. You mentioned that you saw some
topography on the surface of IO that was not volcanic in nature,
cliffs and so on. Are we talking about tectonics
on I or what do you think might cause non volcanic topography
there? Yeah, you need some kind of
mountain building capability, not necessarily plate tectonics,
but so far we haven't really uncovered plate tectonics around
another body other than Earth. But something is moving around
and you're forming mountains, and we see mountain ranges
formed in other places besides the Earth.
What's next in the flight plan or science plan for the Juno
mission? We will continue to go under IO
for the next few orbits, relatively close 10s of
thousands of kilometres away. So we're hoping to continue to
monitor now the South Pole and the volcanoes and we're trying
to tie the volcanic activity to activity that we see in the
Aurora and the magnetosphere to really understand how IO is
really driving this whole system.
But also we're doing occultations.
We actually go behind Jupiter. We're solar powered, so it's a
little bit of a nail biting because when you go in behind
Jupiter you don't have power going on to your solar arrays
for a little while. But we're getting incredible
measurements of the atmosphere by doing occultation.
We pass the radio beam through the atmosphere and we watch it
blink on and off. As you go into an occultation,
you're going behind Jupiter and you can learn a lot about the
density and the properties of the upper atmosphere.
With that, we're also getting closer and closer to Jupiter's
polar region. And so as the perigove of Juno
moves further and further north, the altitude that we pass over
the poles is dropping. And so we're studying these
polar cyclones very, very closely.
And we're able to see now with the microwave radiometer, the
beam is getting to the point where we can resolve these polar
cyclones. And so we're studying those with
multiple wavelengths and looking at how they look in microwave
eyes. At the same time.
We're seeing them in infrared invisible light and really for
the first time looking underneath those polar cyclones
to see how they compare to each other, how deep the roots are,
and compare those two other kinds of vortices that we see
all over Jupiter. And of course, we're also
continue to map out the magnetosphere and the Aurora.
We're getting closer and closer to the North Pole.
So we're really getting to the point where the auroral
accelerations are happening. And so we're going to learn a
lot about how the Aurora and Jupiter get created.
And we're finally going to get to the point where we're
crossing into the rings of Jupiter, which are very, very
close to Jupiter. Very hazardous.
These are very dangerous places to go.
We're kind of an armored tank and our Shields are still
holding, so we're getting closer and closer and we're going to
study the rings of Jupiter as well.
You're saying you're an arm attack, but if you get hit by a
particle in the ring, can you survive that?
We're hoping that we won't get hit, but it's not just the
particles hitting you, it's also the radiation.
We're getting more and more radiation with every orbit.
What is the ultimate fate of Juno going to be?
It either will run out of propellant, which will mean that
we can't point the antenna down to the Earth to downlink our
data. We use the propellant to steer
the spacecraft a little bit and can change its orbit a little
bit, but mostly to turn the spacecraft and point the solar
arrays or the antenna at the Earth.
Or we will have suffer so much radiation that some of the
systems will stop working. And so the end of Juno will be
defined probably by one of those at one point.
We were designed so that we would.
Purposely move Juno into Jupiter to dispose of it to make sure it
didn't crash in to Europa. But now we're past that and we
can't crash into it. Really.
Jupiter's gravity field is too powerful, so we will just die
naturally and eventually the orbit will cause it to fall into
Jupiter, but we won't necessarily control that.
Thinking about future missions, what kind of mission would best
advance our knowledge of the interior of Jupiter's moons, Not
just IO, but some of the other ones where we think there might
be a subsurface ocean. And of course, we speculate that
they might harbour life. Right.
They may be habitable. So there's two missions, one
that's already on its way out. That was the European Space
Agency's mission called JUICE, and it's on its way out to study
Europa and Ganymede and Callisto.
And they'll get a little bit of IO.
They don't get too close to it. Their target is mostly Ganymede.
They'll eventually orbit Ganymede, and that will really
tell us a lot about the interior of Ganymede.
They'll get phenomenal data on the gravity field and the
magnetic field of this body, as well as radar instruments to see
into the ice. And then NASA has a mission that
will launch later this year called Europa Clipper that will
study Europa very closely. It doesn't go into orbit at
Europa, but it gets many flybys of Europa and eventually
Ganymede, and they'll be there together studying these two
moons. And they were being designed
around the same time as Juno, but they just got later starts.
But they're follow ONS and much of the design of the spacecraft
is similar to Juno. So we have a radiation vault.
They both have something like that.
They're both solar powered like Juno was.
Neither of them get really close to IO, so some future mission to
go to IO would be very interesting, either to orbit it,
or even better to get maybe a sample of the plume and bring it
back. What you'd really like is get a
step further, like Osiris Rex got these material from an
asteroid. It'd be great to get samples of
the volcanic plumes or the ices and bring them back to Earth
laboratories someday. Maybe you could land on Europa
or Ganymede and even the ultimate would be go down in
with something and actually sample the ocean.
They're quite deep, probably kilometers deep, maybe many
kilometers, so it's not so easy to do.
If you could decide what a future space probe would be,
where would you go and what would it look like?
Well I'm kind of a greedy scientist so I would want more
than one, but comparing the planets is really important.
Juno uncovered real puzzles about how Jupiter formed and how
its inside works. We didn't really know that and I
think to fully understand that and interpret that we need to
get other examples. So we need to do the same thing
at the ice giants Uranus and Neptune.
They have moons as well. May also be ocean worlds.
You could do a Juno like mission.
We've shown that you can study the body really close and at the
same time get flybys of satellites.
If you could do something like that at Uranus and Neptune, that
would be phenomenal. Even going back to Saturn's
system and studying Titan and Enceladus and Saturn would be
beneficial. Enceladus may also be habitable,
and it's sitting there sending its water plumes out, making it
easy for us to sample them. And these giant planets,
Jupiter, Saturn, Uranus and Neptune represent giant planets
that we see in exoplanetary systems.
And if we're going to understand these other planetary systems
that we're discovering now, we really need to understand what's
in our own backyard. Scott Bolton.
Thank you very much. Thank you.
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