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>> Announcer: NASA's Jet Propulsion Laboratory presents
the von Karman Lecture, a series of talks
by scientists and engineers
who are exploring our planet, our solar system,
an all that lies beyond.
>> Hey, good evening, ladies and gentleman.
How is everyone tonight?
[audience cheers]
Excellent.
Well, anyway, thank you guys
all so much for coming out tonight.
Volcanoes have helped transform the surface of the earth,
the other terrestrial planets, and the moon.
However, the biggest volcanic eruptions in the solar system
are taking place not on Earth but on Io, a moon of Jupiter.
This wonder of the solar system is a fascinating laboratory
where powerful eruptions result from tidal heating.
Despite multiple spacecraft visits and spectacular
new observations with Earth-based telescopes,
some of the biggest questions about Io's volcanism
remain unanswered.
Getting the answers requires a few things:
understanding the difficulties
of remote sensing of volcanic activity,
innovating a new approach to instrument design,
and ultimately, returning to Io.
Our guest tonight will describe how studying volcanoes
on Earth leads to a clearer understanding
of how Io's volcanoes work and how best to study them.
Tonight's guest is a research scientist
at volcanologist here at the Jet Propulsion Laboratory.
He received a doctorate in volcanology
from Lancaster University in the UK in 1988
and has been at JPL for over 20 years.
He was a member of the Galileo NIMS team,
is a co-investigator on the Europa Clipper
mapping-imaging spectrometer for Europa,
has written over 100 papers
on observing and understanding volcanic processes,
and is the, pardon me,
and is the author of Volcanism on Io:
A Comparison with Earth,
published by the Cambridge University Press.
He continues to be engaged in research
into volcanic eruption processes,
spacecraft emission and instrumentation development,
and fieldwork on volcanoes around the world.
He was also a co-recipient of the NASA Software
of the Year Award for the Autonomous Science
Craft Experiment, which successfully demonstrated
science-driven full spacecraft autonomy.
His love of volcanoes is truly undeniable.
Every year, he sends his PhD advisor a birthday card
depicting a work of great art improved with a volcano.
Ladies and gentlemen,
please help me welcome tonight's guest, Dr. Ashley Davis.
[audience applauds]
>> Thank you all very much for coming.
The surface of the moon
and the surfaces of the terrestrial planets
have all been extensively modified
by extreme volcanic activity in their distant pasts,
and these large eruptions are mostly unknown in the manner
in which they emplaced large, vast fields of lava.
But there was one place in the solar system
where such voluminous, powerful, extensive flows,
volcanic eruptions are taking place,
and that is the Jovian moon Io.
Io holds some fascinating views
of how Earth might have erupted in its distance past,
is a key to understand the evolution
of the large Jovian satellites,
and is a great template
for looking for volcanically active exoplanets.
It's truly an amazing place to a volcanologist.
I think I have a pretty cool job,
because I study volcanoes for NASA.
And although this usually means that I spend
most of my time staring at the computer screen
and crunching data and looking at remote sensing
observations of volcanic eruptions,
occasionally, they let me out
to go and play on a real volcano somewhere.
And it's a great job.
It's very exciting, and it's taken me
to the ends of the earth.
This is in the background here we have Mount Erebus.
It is the world's most suddenly active volcano
in Antarctica.
The summit there is a crater with a lava lake in it.
This is in Ethiopia, and again, over on the right,
we see another lava lake on a volcano called Erta Ale.
Now, it's important to think about volcanoes
and what they mean for the evolution of a planet,
but apart from that,
volcanic eruptions are an agent for change
which can affect millions of people very quickly.
This is Mount St. Helens erupting in 1980,
and on Earth, over 250 million people live
within 20 kilometers of a volcano
that can erupt like this.
Apart from that,
moving away from the human element,
volcanoes are a window into the interior of the earth,
or any other planet.
They are an indication of internal heating
which has melted the upper mantle,
and they conveniently transport material
from the inside of a planet to the surface
where it can be observed with instruments on a spacecraft.
And there are many styles of volcanic activity on Earth,
and I've been spending most of my time looking
at low-viscosity basalt-type eruptions
at lava lakes.
A lava lake is the top of a column of magma
connected to a magma chamber.
It's an open system around which magma circulates,
and they're quite rare on Earth.
They tend to crop up in quite extreme environments,
although there is a big one in Hawaii now.
But they're very useful for studying basaltic processes.
I've been studying these on Earth
to better understand what's happening on Io.
Now, the Galilean satellites were discovered
by the great Italian astronomer, Galileo Galilei.
On the ninth of January 1610,
Galileo noted in his notebook
that using this new Dutch invention, the telescope,
he observed Jupiter
and noted these little stars close to Jupiter,
and noted that over the next few nights,
the position of these dots would change,
and came to the conclusion
that these were actually orbiting...
These were actually moons orbiting Jupiter.
So we can jump forward
400 years go the Voyager spacecraft.
There were two of these built here at JPL.
And Voyager flew through the Jupiter system,
and on Io,
made one of the greatest discoveries
of planetary science,
that Io had these large volcanic plumes.
And this was a real revolution in our understanding
of the outer solar system, because up to this point,
it was generally thought that the moons
of the outer solar system planets were small, dead worlds
where over geological time, the geological processes
that were changing them
had basically been damped down into nothing.
They were small, cold ice balls.
But here we have Io being a dynamic, evolving world.
A follow-up mission to Voyager was fittingly called Galileo,
and I was on the Near Infrared
Mapping Spectrometer team, NIMS.
And here we see in the lower right
an observation of Io with NIMS.
NIMS is an instrument that was particularly good
at detecting the heat given off from volcanic eruptions
and sent back a lot of data.
Now, the NIMS, the Galileo main antenna didn't open,
and so there was a restriction
on the amount of data that came back.
And so there are still some gaps on Io
that need to be filled in terms of coverage.
So, here we have the four large Galilean satellites
as imaged by the imaging system on the Galileo spacecraft:
Io, Europa, Ganymede, and Callisto.
Io is closest to Jupiter, and Callisto is furthest away.
And here we have Io, as seen by the camera system
on the Galileo spacecraft.
And the colors of Io's surface
are diagnostic of composition.
If it's yellow, it's rich in sulfur.
White areas are rich in sulfur dioxide.
What's of great interest to me are the black areas
and the red areas.
The black areas are areas of silicate volcanism.
This is where material like basalt
is being erupted onto the surface.
The red areas are thought to be
short-chain sulfur allotropes,
which are evidence of active or ongoing volcanic activity.
So every black or red area on this, in this image
is an active or very recently active volcano.
Now, the amazing thing about Io
is that it's actually volcanic at all.
Here we have Io next to the moon.
And the moon was once very volcanic.
These dark areas are the mare,
and these are layers of basalt many kilometers thick.
But the moon is, as far as we can tell, volcanically dead.
And this is because what drove volcanism on the moon
and what continues to drive volcanism on Earth
is internal heating by the decay of radioisotopes.
This is material that was incorporated
into the planets and moons when they formed.
Now, the laws of physics dictate
that a small body loses heat faster than a large body does.
So over billions of years,
the moon and Mercury and Mars
lost their internal heat to space.
The heat that was driving this vulcanological engine
within each planet slowed down,
and it eventually stopped, and large-scale volcanism
on these bodies was stilled forever.
So this is what happens
with a small body with an internal source of energy.
With Io, something very different is happening.
Io's source of energy
which drives its volcanism is external.
Io, Europa, and Ganymede are in an orbital resonance.
For every orbit that Ganymede makes around Jupiter,
Europa makes two orbits,
and Io makes four orbits.
So every time Io passes, for example, Europa,
Io gets a little kick, and it's taken Io's orbit
and changed it from a circular orbit
into a slightly elliptical orbit,
a bit more eccentric orbit.
And Io gets twisted each time it passes
one of the other two satellites,
and it's this tidal flexing that generates heat within Io
that manifests at the surface as active volcanism.
So it's an external source driving this extraordinary level
of volcanic activity on Io.
It's an elegant cosmic ballet, if you like,
choreographed by the immutable laws of physics.
Now, just to put the majestic scale
of Io's volcanism into some sort of context,
this is the amount of material
that is erupted from earth's volcanoes every year.
Most of this is erupted on the ocean floor
at the mid-ocean ridges.
On Io, this is the amount of material that's erupted
every year to erase any evidence of impact craters.
There are no impact craters on Io,
unlike any other solid body in the solar system.
So there really is a truly astonishing amount
of volcanic activity taking place.
Over the years, we've collected a lot of data
from spacecraft, and this is a mosaic compiled
from the best Voyager and Galileo spacecraft data,
and basically, we've covered most of Io at resolutions
good enough to identify volcanoes from their appearance
and their thermal emission.
And to this has been added a growing dataset,
an astonishing library of observations obtained
with large telescopes based here on Earth.
This is from the Keck telescope in Hawaii.
These are telescopes equipped with adaptive optics.
This is measuring the heat from a whole series of hotspots.
And so putting all of these datasets together,
we've been able to catalog all of the volcanoes on Io
and quantify their thermal emission.
This plot shows 250 volcanoes erupting on,
which have been recently or are currently erupting on Io.
And these range in size from areas of just a few
hundred square meters to vast multiple-kilometer areas
of incandescent material.
Rare thermal outbursts are actually marked here by squares.
These are rare and transient.
So, the size of these symbols,
the larger the symbol, the more energy is coming out.
This is actually on a logarithmic scale.
But the heat flow from Io is not even.
There are areas where we see a deficit of heat flow
and other areas where we see a lot of heat flow.
And this isn't really matched very well to the models
that we have of either shallow or deep heating.
So there's still a lot about the way in which tidal heating
is linked to the delivery of lava at the surface.
Well, let's take a look at some of these amazing volcanoes.
This is a great image obtained by Galileo
which shows a volcano here called Prometheus.
This is a volcano which generates a large plume
about 100 kilometers high
which lays down this circular deposit
which is rich in sulfur dioxide.
And in the middle of this plume deposit
is a lava flow field, which was emplaced
between the Voyager and the Galileo missions
in a period of about 16 years.
So we can go in and take a closer look at this.
Here, we have the flows at Prometheus,
and for scale, we have an image
of Earth's most active basalt volcano.
This is Kilauea in Hawaii.
And this is the area of flows
which was emplaced in about the same time.
So the area of flows here
is well over a thousand square kilometers,
and it's, I don't know, over 2,000 square kilometers.
It's about the area of Rhode Island.
And this was emplaced in just 16 years.
This is particularly interesting volcano,
because what we think is happening here
is that lava is coming up at a vent here
and then passing through a lava cube system
before erupting out at distal ends of the flows,
very much like what we see in Hawaii.
And a logical explanation is lava tube
transportation of new lava,
which is a great way of transporting lava
a great distance without it cooling and solidifying.
But along the way, we see these tantalizingly faint,
small, thermal sources, which could be breakouts
onto the surface or skylights,
which are holes in the roof of a lava tube.
And I'll certainly be coming back
and discussing those later.
Io's most powerful volcano
is in a feature called Loki Patera.
And the general consensus
is that this is actually a large lava lake,
but it's a lava lake 180 kilometers across.
So it's probably better to call it a lava sea.
It is Io's most persistent, powerful volcano.
And we think that it has
a very unique way of being resurfaced.
We think that what is happening at Loki Patera
is that crust on the lava lake forms with time,
and it thickens with time until it gets to a point
where the crust starts to sink,
and then basically the entire surface of the lava lake
is resurfaced by this crust sinking
and the sinking crust being replaced with new lava.
This is an analysis of a single Galileo NIMS observation
that was obtained in 2001, and it shows a temperature map
and age map of the surface from the analysis of the data.
And what this implies is that this resurfacing wave,
if you like, swept around the Patera
at a rate of about a kilometer a day.
So what happens is the Patera resurfaces itself,
and then it remains quiescent for a while
while the crust thickens, and then the crust sinks again.
And it's been doing this periodically for decades.
Well, in 2015, in 2015, the Large Binocular Telescope
Interferometer, which is on a mountaintop in Arizona,
collected this truly astonishing set of observations
which shows Europa passing across
and eclipsing or occulting Loki Patera.
So Loki Patera is here,
and this is Europa passing across in front of Io
between Io and the telescope on Earth.
And what this means is that as Europa's edge
passes across Loki Patera,
it covers up the Patera in one direction,
and we get this light curve here as light is cut off
and heat is cut off.
But as Europa uncovers Loki Patera,
we get this curve with the limb
going in a different direction.
And so by fitting these little squiggles in the dataset,
we created, and this was an effort led by Katherine de Kleer
who's now at Caltech.
We created the highest spatial resolution map
of Loki Patera's surface that's ever been obtained,
even including data from spacecraft.
We managed to create a map over the entire Patera floor.
And fitting this lava lake model to it,
looking at the distribution of temperatures on the surface
from which you can infer age,
'cause the older the surface, the cooler it is.
The explanation that we came up with
for this particular temperature distribution was this,
two resurfacing waves sweeping around the Patera
to form this resulting temperature distribution,
which was observed
by the Large Binocular Telescope Interferometer.
And this is something
which is consistent with previous observations.
It's a really nice vindication
of this lava lake resurfacing model.
A more active lava lake on Io is at Pele,
and Pele is at the center of this bright red deposit,
which is a plume deposit, a plume fallout.
It's a plume that's hundreds of kilometers high,
and it's led to this deposit on the surface,
rich in short-chain sulfur allotropes
about 1200 kilometers across.
And we think that Pele has every appearance of an active,
over-turning lava lake with the plume basically
forcing its way up through the middle of the lake
and disrupting the surface, yielding,
revealing high temperature lava.
And it's much larger, it's about 38 kilometers across
and much larger than its terrestrial equivalents.
This is the Kupaianaha lava lake in Hawaii.
Terrestrially, lava lakes
are maybe 10 or 20 up to 100 or 200 meters in diameter.
Io's volcanoes, Io's lava lakes seem to be hundreds
or even thousands of kilometers, square kilometers in size.
Loki Patera itself, Loki Patera has a surface area
of over 21,000 square kilometers,
which makes it even larger than West Virginia.
Io's most powerful eruptions, thermal outbursts,
are now known to be caused by large lava fountains
gushing forth from long fissures.
And these sort of events were actually seen,
a couple of them were seen by Galileo.
This is what's happening along this fissure here,
and this is the result of saturation.
Because so much energy was being received by the spacecraft,
the detector saturated.
And this is a problem
that we've come across time and time again
with trying to image these very powerful events.
We now see these things from Earth-based telescopes.
They were actually discovered by Earth-based telescopes
back in the 1990s.
But we're continuing to discover these.
They're quite rare, and they're quite short-lived,
but they're very powerful.
In 2013, we saw two of these at Rarog
and Heno Patera in the southern hemisphere of Io.
This is an interesting image,
because it does show that that's short wavelengths,
that Loki Patera does not emit a lot of energy.
Most of the energy being emitted from Loki
is at longer wavelengths.
And what that tells us is that generally speaking,
Loki is a relatively cool surface
compared with what we see at these outbursts.
So for the purposes of determining
eruption temperature of the lava,
Loki Patera may not be our best candidate,
whereas something like Pele,
where we have overturning lava lakes,
an overturning lava lake on a much shorter time scale
is a better candidate.
So by looking at all of this data
and doing a lot of modeling, we come up with,
we've come up with a classification schema
where we can identify the characteristic thermal
fingerprints of different styles of volcanic activity.
The most powerful eruptions are these outburst eruptions,
these large lava fountain events.
We have the Pele overturning lava lake right here,
and at the bottom,
we have the small but powerful lava tube skylights.
These are small but very high-temperature.
I'll be talking more about these later.
So, Io is a fascinating body
in terms of, it was the first body
where we really did see active resurfacing processes.
But the Voyager, Cassini,
and Galileo missions have shown
that there were many other satellites in the solar system
which have this dynamic, evolving structure.
For example, we have Enceladus,
which is one of the moons of Saturn,
which has water plumes erupting
from the south polar region, and we have Titan
and the Jovian satellite Europa,
which have geologically young surfaces.
But Io and all of these bodies are,
to some extent, tidally heated.
But Io is the most tidally heated body in the solar system,
and it's probably the best place to study
this extreme limits of this process.
So the big picture as it stands is that we know
that Io and Europa are tidally bound together,
but how much heating,
and where this heating is taking place
within the satellite is not really well constrained.
But as tidal heating is most pronounced at Io,
it's really knowing Io's interior condition
that gives us some insight into further constraining
how much heat is being input into Europa.
So, on Io, it's the eruption temperature of Io's lavas
which could be diagnostic of interior conditions.
And so, looking to Io's volcanoes to get this data
is what we need to do
as a way of constraining the interior state of Io.
So the big question in the wake of the Galileo mission
regarding volcanism and Io
is what is the composition of the silicate lavas on Io?
This reflects what's happening inside.
We know that Io's volcanism is dominated
by low-viscosity, quite fluid lava, like basalt.
Basalt erupts at about 1140 centrigrade,
and this is the most common
volcanic material in the solar system.
But it's also possible that with Io, on Io,
that we have a type of lava called ultramafic lava,
one of which is a Komatiite.
And this erupts
at hundreds of centigrade higher temperatures.
And this is interesting to us because ultramafic lavas
were once common on Earth in Earth's distance past,
and it might have been a time
when this reflected a hotter mantel in the earth.
So if ultramafic lavas are indeed erupting on Io,
Io would truly be
a window back into Earth's geological past.
Now, the hotter the lava, the more interior heating
is taking place, and the more liquid the interior.
But it's very difficult to tell the difference
between ultramafic and basaltic lavas by temperature alone.
Firstly, you have to look
at a very narrow part of the thermal emission spectrum,
and secondly, the problem here, and this is something
that has bedeviled efforts to do this with remote sensing
is that we're trying to tell the difference
between a lava that erupts at a very high temperature
and something that erupts at a very, very high temperature.
So, Komatiite, it really takes a couple of seconds
for a Komatiite erupting at this temperature of, say,
1850 Kelvin to cool down to the temperature
at which basalt erupts.
And so it's very difficult to tell
one from the other, and if you're going to go to Io
and look at styles of volcanic activity
to try and do this,
only certain styles of volcanic activity will do.
And the first is lava fountains.
And this is something we have to get pretty close to
and image, say, the base of a lava fountain
before the lava that's gushing out of the ground
can cool too much.
And the problem with this
is that these are relatively rare, and it's impossible
to predict where these are going to happen.
Lava tube skylights are a particularly good candidate
for doing this, because they're small,
you have a very high temperature gradient
between the lava tube skylight and the surrounding area,
so these things stick out very well,
and the temperatures inside
are very close to eruption temperature
because the lava tube itself is highly insulating.
And then we have lava, lava lakes.
And what we're interesting about in lava lakes
is the fountaining that takes place,
because it's the fountaining events
that reveal the lava at its highest temperatures.
So, I've been traveling around and looking at lava lakes
and taking models of volcanic activity
to understand how best to measure
lava eruption temperature.
So, a few years ago, I went to Erebus in Antarctica.
This is, these are observations obtained
by a satellite in Earth orbit, Earth Observing-1,
and this is a visible image,
and this is an infrared image.
And we can see the lava lake here with a smaller pit.
And I'm actually standing in a pixel about here
as this was taken.
And here I am at about 13,000 feet on Mount Erebus,
and it's a bright, sunny, summer day,
and the temperature, the ambient temperature
without wind chill is about -40 centigrade.
And at the summit...
Oh, this is our camp.
This is at about 11,000 feet.
This is the summit of Erebus.
At the summit, there's a crater about 600 meters across,
and it's about 250 meters deep.
And in that crater there is an active lava lake
of a lava called phonolite.
It's quite a rare composition.
And this is the lava lake itself.
It's about 38 meters across, and one of the most
extraordinary things I've ever seen.
And I took down a thermal imager,
a FLIR thermal imager with me, and this,
this is the data, some of the data that was collected.
And what we see here is that lava is welling up
at the center of the lake,
forming a crust, which then moves laterally,
and then the lava goes down at the edges.
And this has been circulating around between the surface
and the deep-seated magma chamber,
about three or four kilometers down.
So, this was a great test of a model that was created
to determine the temperature and area distribution.
This is just a cartoon of that model.
We have lava rising up, spreading and then sinking.
So there is a mathematically-defined
progression in cooling across the surface of the lake.
And if you integrate over that,
and then you can compare that with the data,
this is what we got.
And this was a great pleasure to me
to actually do this, because the model fit to the data.
We produced the thermal emission
as a function of wavelength, the total power emitted,
and the area of the lava lake just down to a few percent.
So this is very gratifying.
There was a slight discrepancy in the fit
between the model down here,
and that is just basically
because the model used a basaltic composition,
and it was only the lava eruption temperature
that was different.
And that's why there's a slight gap here.
So it looks like the model is actually very sensitive
to temperature, and this improves our confidence
of fitting data that we get from the spacecraft.
Now, the resurfacing mechanism at Erebus
was generally very quiescent,
but when I was there in 2005, every six to nine hours,
the lava lake would resurface itself like this.
[Ashley mimics explosion]
[audience laughs]
I have to do my own special effects.
But that's what it sounded like.
[audience applauds]
It was pretty impressive when this thing blew.
So, yeah, this is a Strombolian eruption,
and it basically throws out lava bombs
up to three-quarters of a kilometer.
So, you gotta be careful.
[audience laughs]
Okay, all the bad acting aside,
the guy under the rock, his name's Alexander Gurst.
And at the time, he was a graduate student
at the University of Hamburg,
and now, he's an astronaut
in the European Space Agency Astronaut Corps,
and he's already spent one tour
on the International Space Station,
and he's mission commander on a mission
that's going to be launched in 2018.
Well done, Alexander.
So, the results from the field trip to Erebus
and all the data analysis
is that we see that lava lake thermal signatures,
the characteristic thermal signature
of a lava lake on Earth
and its contemporaries on Io are actually pretty similar.
The model fits used to interpret the Io data,
the model was actually developed to interpret Io data
actually works really well on terrestrial data.
So that's a good test.
And the analysis appears to be sensitive
to eruption temperatures, which is important.
This is all very well to Erebus, but things,
how do things like with a better analog for Io?
And so a few years later, actually, I was asked
to go out to this volcano in Africa, the Erta Ale volcano
in the Danakil Depression in the Afar region of Ethiopia
by the BBC, who are filming a series
called Wonders of the Solar System.
Io is obviously a wonder of the solar system,
and so they wanted to talk to me about it out there.
I jumped at the chance.
Erta Ale is located at the northern end
of the East African rift system.
This is where Africa is pulling itself apart,
and it's a basalt lava lake.
And here it is.
In 2009, it was about 55 meters across.
There was a lot of vigorous churning around at the edges
and the occasional lava fountain in the middle,
and it's one of the most extraordinary things
that I've ever seen.
And so here I am on the summit
of Erta Ale on a bright, sunny, summer day,
and the ambient temperature is 133 Fahrenheit.
It's 56 centigrade.
Sorts of it's not surprising I look a little pink.
Again, with a thermal imager.
These lava lake tend to be in these really,
you know, extreme environments.
Here I am again with another thermal imager.
And this is an hour in the life of the lava lake
compressed down into about 10 seconds of time lapse.
And what I'd like to point out is a small lava fountain
just about here.
There it goes.
This is where the crust has been disrupted,
and areas of very high temperature are being revealed.
And that's what we're interested in.
So, I took a look at these data to determine
what the effect would be of any kind of delay
getting data at different wavelengths.
A traditional way for spacecraft, like the Voyager,
spacecraft images to work is,
you take an image of the surface
through one filter.
You move a filter wheel.
You take another image, do another filter wheel.
After another filter on the wheel,
you move the filter again.
You take another image.
Then you combine those images together,
and you get a color image.
That's fine for planetary surfaces,
but where we have something that is changing rapidly,
because it's actually cooling very fast,
what is the effect of that
when you try this experiment again?
And this is what we found,
that with even a second delay
in taking data at different wavelengths,
we got these massive...
Here we go.
These massive changes in derived temperature,
which really does make it very difficult to have
any confidence in an actual temperature derivation.
But when you cut the difference in time
down to a fraction of a second,
we get a much smaller amount of variation.
Of course, this would be, this would be a flat line
if the data were obtained simultaneously.
So, what we found from Erta Ale is that temperatures,
that areas of target temperatures change so rapidly
that observations have to be obtained very fast,
or ideally, simultaneously at different wavelengths.
Now, with Galileo data, we tried deriving temperatures
from Galileo data by combining different SSI frames
and combining NIMS data with SSI data,
and we found that with seconds and minutes
between observations,
it damages our confidence in the results,
because the target that we're looking at
was probably changing in that time.
Now, this is not a criticism of Galileo
by any means of the imagination,
because the instruments of Galileo were simply not designed
to do what we'd like to do with the next mission.
We see as far as we do
because we stand on the shoulders of giants.
So, this is not a criticism of Galileo at all.
The upshot of this is that observations
have to be obtained in a fraction of a second.
So, we're really getting close now
to what we need to overcome these problems.
We have a very good handle
on the derivation of the style of volcanic activity
from studying volcanoes on Earth
and studying volcanoes on Io.
On that note, there was a paper published just last year
where we quantified the thermal emission
that you would get from a lava tube skylight
for both basalt and ultramafic compositions.
So now we have the distinctive thermal fingerprints
for both of these compositions to help us analyze any
new spacecraft data that we might get on volcanism on Io,
or the style of volcanism on Io.
We have a very good handle on the rapid cooling of new lava.
We know how the process works,
and we know some of the problems
that have to be overcome with that.
And with lava fountains
and with fountaining in lava lakes,
there is still the problem
of the unpredictable magnitude of thermal emission.
Because if too much radiance is captured by the detector,
it will saturate, and then the data are no good
for deriving eruption temperature.
But there's a number of ways of doing it,
and here's one.
This is an effort being led by Alex Soibel here at JPL.
It uses something called a HOT-BIRD detector,
which was invented here at JPL,
and an integrated circuit
that was invented at MIT Lincoln Labs.
And it splits the signal coming in.
It obtains data simultaneously at multiple wavelengths.
For our purposes, the detector and the circuit
are non-saturating, so there's no saturation effect,
and it's got a fast integration time.
So this is just one approach that can be used
to get the data that we need
to measure lava eruption temperatures on Io accurately.
So, now, we really do have all of the pieces of the puzzle.
We can identify different eruption styles on Io.
We can understand...
We have a good understanding of how these
different eruptions behave thermally and temporally.
So we really do know what observations to make.
We have some designs
for instruments that collect the data,
and we have models that can be used
to interpret the data once obtained.
And now the only thing we're missing now are new data.
So, the unlocking of Io's secrets
has been an incremental process.
The Voyager spacecraft discovered
that Io was volcanically active,
and we did so with instruments that were not designed
for looking at any kind of silicate volcanism.
This was completely unthought-of
when the instruments were designed in the first place.
Galileo discovered that silicate volcanism
was the dominant from of volcanism on Io,
and now the question is,
what is the actual composition of the lavas?
Is it uniform across Io, or are there different compositions
being erupted in different places
which reflect the depth of origin of these lavas?
Are they hot, or are they very hot?
So, really, a new mission is needed to get back to Io,
and there've been different missions
proposed over the years.
This is one that was proposed a couple of years ago.
It may be proposed again by Alfred McEwen
at the University of Arizona.
It was called the Io Volcano Observer or IVO.
IVO and other missions like it would be the first mission
sent back to Io dedicated to study Io's volcanoes
and the interior processes
with instruments designed specifically to overcome
the problems, the problems that are inherent
in trying to understand what's happening on Io,
to finally nail down eruption temperatures,
constrain interior state,
and then this can be applied also to Europa.
So in conclusion,
we really truly are living in a new,
in a golden age of exploration.
We know the big Io questions can be answered,
and to a volcanologist,
Io is a truly amazing place.
It's a window into Earth's past.
It's key to understanding Jupiter's satellites.
It's a volcanologist's paradise.
Thank you very much.
[audience applauds]
If anyone has any questions, please use the microphone
set up in the middle of the room.
>> Hi, great presentation.
I had a quick question with regards
to potential for an atmosphere on Io.
Is there any indication there was an atmosphere,
or is there an atmosphere?
Will there be an atmosphere in the future?
>> There is a very, very thin atmosphere of sulfur dioxide
which appears to freeze out at night.
It's not as thick as Earth's atmosphere.
We're talking about something that is just a tiny fraction
of a bar, and it's basically sulfur dioxide
that's generated from the volcanoes themselves
by lava flow across the surface
and melting and remobilizing sulfur dioxide gas and sulfur
on the surface.
It's remobilizing ices.
>> Hi, I'm just wondering if you have any plans
to visit more volcanoes,
or if there's any specific ones you'd like to go to?
>> I try to visit as many volcanoes as I can.
I made my first trip to Etna this year,
which is very exciting.
That's where I encountered sort of the mantra
of the volcanologist, which was,
you should have stayed an extra couple of days.
Usually, it's you should have been here last week.
In this case, I left a couple of days
before it erupted quite spectacularly.
I would like to go back to Erta Ale
with new equipment.
I spend a lot of time at Kilauea,
'cause Kilauea is convenient, it's relatively close,
and it's a great analog for a lot of the styles
of volcanic activity that we see on Io.
So it's a great test bed,
and it's a great learning experience to go out and watch
the eruptions take place.
Yeah.
>> Hi.
I understand there are about 400 active volcanoes on Io
contributing to the ejecta and the plasma torus.
And my question is, are there any dormant volcanoes on Io
or do you know of any that are going dormant?
>> We've identified 250 locations
where there's been active or recent volcanism,
and there are, as you quite correctly say,
there are about 400 sites on Io which look like dormant...
There are 400 sites on Io which
have the appearance of past activity
as well as the current activity.
So yes, there are many sites on Io
which look as if they once were volcanic,
but don't appear to be volcanic now.
I don't think that there's been any correlation
between where the activity is taking place now
and where it seemed to have taken place at some other time.
So there may be something hidden in those data
which reflect a shift in maybe regional volcanism,
but no, I can't say anything definitive
about that right now.
>> Thank you.
>> Yeah.
You're welcome.
>> So, first of all,
thank you very much for your presentation.
It's been very eye-opening.
[audience laughs]
Pun not intended, I promise.
So my question is, have we been able
to detect a magnetic field around Io, and if not,
what's the theory for what's missing
in development for that magnetic field?
>> You know, I'm not sure of the answer.
The Galilean Magnetometer did some measurements
as it went past Io which did infer
that there was, through magnetic induction,
that there was a global magma ocean.
I'm not sure about the strength and size
of Io's magnetic field.
>> Thank you very much.
>> Hi.
My question is, do we have an understanding
of the mechanism from placement of the magma at the surface?
Is there some sort of tectonism going on
that is a mechanism for that?
>> Right.
We don't think there's any sort of global tectonics
the way we see global tectonics on Earth.
Instead, we have a heat pipe mechanism
where lava or magma works its way up from the top
of the lithosphere to the surface.
What helps it get there seems to be a trend
for large faults in the crust providing planes of weakness
and reducing stress, horizontal stress,
which provides pathways for lava to get the surface.
The problem with Io is it's being resurfaced so fast
that the crust is getting compressed down.
And so very large horizontal stresses build up,
and these stresses are relieved
by large crustal blocks tilting
and by faulting in other areas.
And these seem to provide pathways for lava
to get to the surface.
So the thick, the thick crust seems to be fractured
sufficiently to allow the passage of lava,
the passage of magma, to the surface in many locations.
But there are no plate tectonics like what we see on earth.
>> Audience Member: It's fracturing, but there's no...
>> It's fracturing, but there's no subduction,
and there's no sort of...
There don't seem to be any spreading centers.
>> Okay, thank you.
>> All right, you may not be able to answer this,
but I can't help but wondering if the Europa Clipper
might be carrying an instrument that perhaps
in an extended mission could collect
some of the data that you're looking for from Io.
>> Yep.
We're still trying to figure out what to look
at on Europa with the Europa Clipper,
and Europa Clipper is not going to make any close passes
to Io because Io is deep in Jupiter's radiation belt.
So I think the best chance for understanding Io's volcanism
is with a dedicated Io mission.
>> Two questions.
The second one I guess was already answered,
that we're not going to...
The Europa Clipper isn't going to help here.
So, if the energy for all this activity
is coming from the tidal forces
between different satellites,
is there enough energy in that orbital motion
to power the heat for the whole lifetime of the solar system
and for a billion years in the future?
>> It looks like Io...
One of the theories about Io and Europa and Ganymede
is that they move in and out of orbital resonance.
So what we see is a complicated byplay
between orbital dynamics and the interior structure of Io,
Europa, and Ganymede.
So it looks like, on a scale
of maybe hundreds of millions of years,
Io and the other satellites
may move in and out of the resonance,
which would actually cut off volcanism on Io.
So it might be that Io is going through at the moment
a very high level of volcanic activity,
'cause it's at a peak in this scale.
We don't really know,
but that's important because you get to the point
where Io's interior is so fluid that the tidal forces
end up moving, just basically moving the fluid around,
and volcanism will actually come to an end
once it moves out of the resonance.
Once it's out of the resonance and the tidal forces
can get a grip on a solid Io again,
it will move back into resonance,
and the volcanism will start again.
And this might happen so quickly
that we get total mixing or total melting of the interior
so that we go back to basalt,
we go back to possibly ultramafic material.
It's a conveyor belt of volcanic activity
that moves so fast
that we don't get highly-evolved melts on Io.
We don't get highly silicate, highly silicon-content lavas
like we see on earth.
We don't get a secondary crust forming
or tertiary crust forming.
So, it might be that Io is heated back to an extent
where it's a primitive interior composition,
which is why it's interesting,
because that would reflect the early earth.
>> Very interesting.
Thank you.
>> Great talk, Ashley.
I have a question and a comment.
The question is,
given all of the modeling that you've done
and now it looks like we also see cryovolcanism,
as you mentioned previously,
in places like Titan, Enceladus, and Triton.
To what extent can you apply the models
that you've developed for sort of magma to cryomagmas,
and then the comment is that today does happen
to be the 14th anniversary of when Galileo
did its plunge into Jupiter's atmosphere.
So it's quite appropriate, I think,
that you gave this talk tonight.
>> Right, yes.
The physics of the eruption and cooling and emplacement
of cryolavas, it's very similar to the modeling
that I've been doing, and basically
it's just the physical input values that are changing.
So, yes, I've looked at the emplacement of cryolavas
on Titan and some of the effects on Enceladus as well.
Okay, we have some questions,
questions from the internet.
So, FindingFreedom asks,
"Could debris and particles from Io's volcanic eruptions
"damage spacecraft orbiting or flying by the moon?"
The answer is yes, they could.
Galileo itself had its orbits,
its orbital trajectory changed to avoid a large plume
and ended up running into another plume.
[audience laughs]
That's just the way it is.
But it is possible to damage a spacecraft,
and that really depends on what kind of plume is erupting,
how thick it is,
how much material has been incorporated into it.
Your spacecraft is basically flying through this
at about six or seven kilometers a second,
so even small particles can do damage.
Alex asks, "Do the volcanoes act differently
"being directly exposed to the vacuum of space?"
And that's a good question.
On earth, Old Faithful goes up about 30 or 40 meters.
On Io, under the same eruption conditions,
because you are erupting into a vacuum
and because gravity is lower.
If it was just gravity lower,
the plume would be six times higher,
but because you're erupting into a vacuum,
you get much more expansion.
You get much more bang for the buck.
Old Faithful would be 38 kilometers high.
So erupting into a vacuum means that
if there's any gas exsolving from the lava,
you tend to erupt much higher velocities
than on Earth where things are a little controlled
by atmospheric pressure.
And finally, Paige asks,
"Is there topographical information
about Io's lava lakes?
"I'd be curious to see
"the heights and depths of Loki Patera."
We have a pretty sparse dataset where there's high enough
resolution to make any kinds of measurements
of lava flows and the lava lake.
The lava lake just seems to be completely flat.
We see specular reflection off the surface,
which kind of enhances the idea
that it is, in fact, a lava lake.
There is only one measurement, direct measurement,
of the thickness of a lava flow on Io,
and that is about 10 meters thick
at a location called Pillan Paterae
where there was a big eruption in 1997,
which emplaced really large lava flows,
which, in the space of a few months,
covered 5600 square kilometers.
And these flows ended up about 10 meters thick,
about 30 feet.
Okay, that's the last question.
Does anyone else have any questions?
Well, thank you very much for coming tonight.
[audience applauds]
Thank you.
[bright instrumental music]
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