Jupiter’s moon Io is a wildly volcanic moon that spends its time bathed in Jupiter’s
intense radiation torus.
In contrast to many moons of the solar system, it is neither icy nor wet.
It is the most geologically active object in the solar system powered by tidal heating
as the moon is flexed by the enormous gravity of Jupiter and the other moons of the system.
The tidal forces at Io are actually so great that they deform its crust by tens of meters,
launching the massive amounts of volcanism we’ve seen present on this world, which
is only a little larger than our own moon.
Given all the volcanism and radiation, the surface of Io is one of the most dangerous
planetary surfaces in the solar system, one that humans may never set foot on.
Indeed, this image taken by the Galileo probe about a year apart, show a dormant volcanic
region coming to life and flinging volcanic bombs aloft.
But in this case, ejecta from the volcanoes travels far higher off the moon and returns
slower due to the lower gravity, which again is on level with our own moon.
One enduring oddity about Io is that whenever it spends time in darkness with Jupiter blocking
the sun, something strange happens that causes the moon to appear much brighter than normal
for a short time after it emerges back into sunlight.
It’s thought this might be a phenomenon of cold volcanic sulfur dioxide that might
form a kind of light reflective frost on the surface that rapidly evaporates upon exposure
to sunlight causing the brightening and then subsequent dimming back to normal.
On the other hand, Io’s emission of sulfur dioxide varies wildly and rapidly, depending
on the levels of volcanic activity, so it remains speculation as to if that’s really
what’s causing the brightening effect.
And that’s not the only strange thing about Io.
You would normally think it would be the last place in the solar system to look for microbial
life, but it actually isn’t.
Io once had as much water as any of the other galilean moons of Jupiter, and while most
of that water is gone now from the surface, there is probably still significant amounts
of it subsurface.
Active volcanism can produce several things that might favor abiogenesis.
One of these is the formation of lava tubes.
We have these here on earth, where subsurface lava flows create natural caverns, some that
run for significant distances.
Here on wet earth, moisture tends to be plentiful in such places, and may also be so on Io.
Is it possible for some holdout of microbial life from early in Io’s history to still
be eking out a living on the moist walls of a lava tube?
It’s anyone’s guess, but the nutrients for life do seem present there.
And there is the recent discovery of how RNA is generated, the key factor being the presence
of basaltic volcanic glasses.
Io has these, as does Earth, Mars, and probably Venus and a number of other once volcanic
places such as the moon.
It’s also possible that while Io may have never quite spawned life, it may have spawned
an active RNA world where RNA is possibly being generated to this day.
Unfortunately, we’re probably a long way off from ever exploring the surface of Io
even robotically, everything about this environment is harsh, so priority will be given to Europa
over Io, though it may be explored to some degree before Callisto and Ganymede.
Another enigma of Io is that it doesn’t really like to behave as our models predict
it should.
Models of the heat profile of Io predict where we should see active areas of volcanism.
Trouble is, we don’t, the volcanism is all over the place shifted very differently than
what’s predicted.
There's clearly something going on there that we don’t understand.
One possibility is that Io may have a gigantic magma ocean not far below the surface altering
the equation.
Evidence for this comes in the form of an induced magnetic field at Io.
For that to be the case, and show the characteristics measured, there would need to be a magma ocean
about 50 kilometers below the surface, extending down to about 100 kilometers.
If so this would make Io similar in a roundabout way to the other three Galilean moons in that
they’re all ice shell moons supporting subsurface oceans, whereas Io is the evil brother that
is a rock shell moon with an ocean of molten magma deep below.
But hidden within the history of astronomy there lies another curious mystery regarding
Io.
In 1983, a team at the Jet Propulsion Laboratory was imaging Io as it came out of eclipse at
Jupiter.
Another team at the University of Hawaii was doing the same thing at the same time.
The JPL team were taking images at 3 minute intervals, for a total of 14 images.
The team at Mauna Kea were taking images at 2 minute intervals.
One frame of the JPL observations showed a massive unexplained increase in brightness
at Io in one single frame.
The team at Hawaii did not record this, rather the frame fell right in the window on either
side of the brightening meaning that whatever caused it, it was a very rapid, short lived
flash.
This does not seem to have been a malfunction of the detector that took the frame, and it
never did anything like that before or since, so the flash appears to have been real.
In addition the background didn’t change.
The question is then, what could have caused Io to rapidly increase in brightness to the
tune of 50 percent greater than normal in such a short period of time?
The go to explanation here would be an impact event and that the teams just happened to
catch when an asteroid hit Io.
The problem with that though is that images taken by Voyager in 1979 compared to those
taken by Galileo two decades later don’t show any fresh impact craters, and that’s
not enough time for Io to have completely erased one with its volcanism.
Another option is the volcanism itself doing it, somehow a huge explosive event might have
caused the brightening, the problem there is that volcanism doesn’t really do that
on scales that transient and short lived.
That left a rather odd scenario where it was actually Jupiter getting hit by a sizeable
asteroid of at least 5 kilometers diameter producing a flash of light that was then reflected
off of Io’s surface and spotted by the observers.
This is actually a kind of phenomenon seen in the cosmos relatively regularly when the
right conditions are met.
Whenever a huge flash happens in the galaxy, such as that from a nova or supernova, there
can sometimes be clouds of dust and gas relatively nearby that reflect the flash.
But given that it takes time for light to traverse space, this light echo can be delayed
significantly.
So the supernova flash itself is long gone, but a delayed echo of it can be seen in the
surrounding area.
These have also been noted in very distant galaxies, suggesting the shut down of a quasar’s
active galactic nucleus, but a remaining light echo still being visible by luck.
But even the Jupiter impact hypothesis has a problem.
In 1994, comet Shoemaker-Levy 9 impacted jupiter and should have produced measurable flashes
on some of the Galilean moons.
No echoes were detected, suggesting that fireballs don’t really produce reflected flashes of
this nature, they apparently normally not bright enough.
So if it was an impact, it would have had to have been enormous, and should have left
a significant and very visible blemish on Jupiter’s upper atmosphere as Shoemaker-Levy
9 did.
There the comet hit, which had been torn apart causing multiple impacts, and it did on the
backside of jupiter.
But the blemishes were long lasting and rotated into view in the hours after the impact.
This was not seen in the 1983 event.
That leaves one other weird possibility.
Jupiter has some of the most violent, powerful lightning in the solar system.
The Jovian lightning is a mystery in itself.
Before 1979, it was hypothesized that lightning might be happening at Jupiter.
In 1979, it was confirmed by Voyager 1 which picked up radio signals that are characteristic
of lightning.
You can see this phenomenon by turning on an AM radio during a thunderstorm, you’ll
get broadband interference from nearby lightning strikes.
But at Jupiter, there was a difference, for some reason the lightning there appears at
a completely different frequency range than here on Earth.
Subsequently Galileo and Cassini on its way to Saturn during a gravity assist flyby also
detected radio evidence of Jupiter’s active lightning.
Lightning is very frequent on Jupiter.
Even more information came with the Juno Spacecraft, which detected 377 lightning strikes during
its first 8 flybys, greatly increasing our understanding of the phenomenon.
But it has also revealed new mysteries.
We still have mysteries regarding lightning on earth, with Jupiter it’s worse.
For example, Jupiter’s lightning happens predominantly at its poles, especially the
North one.
One earth, the opposite is true, lightning gets more common the closer to the equator
you get.
Why it’s stronger in the north than the south seems to be due to a cluster of long-lived
storms in the north, compared to the relatively or at least currently quieter south.
It has to be said here that some of the major differences between lightning on the two planets
can be chalked up to Earth and Jupiter being very different types of planets.
Jupiter is much larger, has markedly different weather and a completely different atmosphere.
It also receives overall less sunlight, which plays a factor in weather, and earth actually
has a solid surface with a thin atmosphere.
Jupiter may have a solid surface deep in its core, but Jupiter is thought to have a thick
atmosphere that transitions into a rather odd substance, metallic hydrogen.
While hydrogen is grouped on the periodic table with the alkali metals, it doesn’t
usually behave like one.
But decades ago Wigner and Huntington predicted that under enough pressure, as is present
deep inside Jupiter, hydrogen might start to exhibit some of the properties of a metal.
Even stranger there is a prediction that metallic hydrogen is metastable, or at least can be,
meaning that you can ease off the pressure and it will remain in its metallic state.
Attempts to create metallic hydrogen in the lab have been inconclusive and debated, but
if it exists at Jupiter it would comprise a liquid ocean.
Needless to say, there are a lot of complex possibilities and factors involved with the
generation and behavior of Jupiter’s lightning.
It may even be the case that Jupiter’s intense magnetic field also plays a role.
And there is a further confounding problem, Jupiter seems to have several different types
of lightning.
From what we know from spacecraft data, Jupiter’s lightning seems to originate in water clouds
deep in the atmosphere, not unlike Earth’s water clouds as far as lightning is concerned.
But Juno found a second type of lightning that seems to originate very shallow in Jupiter’s
atmosphere.
This type of lightning is notably weaker than Jupiter’s deep gigantic flashes.
Trouble is, it’s too cold for liquid water droplets at this altitude.
It’s been suggested that it’s possible in this layer to have a mix of ammonia and
water forming hail.
What’s thought to happen is Jupiter’s violent storms toss water high into the atmosphere,
where it freezes.
Over time however ammonia gas melts it, basically like anti-freeze.
These ammonia and water mixed droplet then allow for the formation of lightning as the
intermix with other ice crystals welling up from below.
This is backed up by the finding that some areas of Jupiter’s atmosphere lacks ammonia
for no good reason.
But back to the mysterious flash at Io.
We know from Earth’s lightning, that megaflashes can occur that are significantly different
than normal lightning flashes.
In fact, one recently announced megaflash was a lightning bolt that extended an amazing
708 kilometers across Brazil.
These kinds of flashes could be very much stronger at Jupiter if they occur in especially
the higher region flashes.
Recent work has shown that Jupiter’s deeper lightning can extend high into its atmosphere,
so it’s possible that the brightening at Io really was a huge flash of lightning in
Jupiter’s upper atmosphere reflecting off its surface.
If you were standing on the surface of Io and avoiding the lava flows and volcanic bombs,
such a sight as megalightning on the dark side of Jupiter would be something to behold
indeed.
Thanks for listening!
I am futurist and science fiction author John Michael Godier currently welcoming a bunch
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