From the discovery of the moon, to what makes
it so volcanic, and more!
Join us as we explore Io: Jupiter's Volcanic
Moon!
8.
The Discovery Of Io
In many ways, Io is one of the more popular
moons of Jupiter.
It's been referenced many a time as we'll
note later.
But how did we learn about this very special
moon?
The first reported observation of Io was made
by Galileo Galilei on 7 January 1610 using
a 20x-power, refracting telescope at the University
of Padua.
However, in that observation, Galileo could
not separate Io and Europa due to the low
power of his telescope, so the two were recorded
as a single point of light.
Io and Europa were seen for the first time
as separate bodies during Galileo's observations
of the Jovian system the following day, January
8th, 1610 ( this is used as the discovery
date for Io by the IAU).
The discovery of Io and the other Galilean
satellites of Jupiter was published in Galileo's
Sidereus Nuncius in March 1610.
In his Mundus Jovialis, published in 1614,
Simon Marius claimed to have discovered Io
and the other moons of Jupiter in 1609, one
week before Galileo's discovery.
Galileo doubted this claim and dismissed the
work of Marius as plagiarism.
Regardless, Marius's first recorded observation
came from 29 December 1609 in the Julian calendar,
which equates to January 8th, 1610 in the
Gregorian calendar, which Galileo used.
Given that Galileo published his work before
Marius, Galileo is credited with the discovery.
But the end of the "discovery" did not end
there.
Because for basically 250 years various astronomers
tried to learn more about Io.
But because of its place in space all they
could usually see was a ball of light.
It would take a while for them to start to
parse out the details of the moon.
Improved telescope technology in the late
19th and 20th centuries allowed astronomers
to resolve (that is, see as distinct objects)
large-scale surface features on Io.
In the 1890s, Edward E. Barnard was the first
to observe variations in Io's brightness between
its equatorial and polar regions, correctly
determining that this was due to differences
in color and albedo between the two regions
and not due to Io being egg-shaped, as proposed
at the time by fellow astronomer William Pickering,
or two separate objects, as initially proposed
by Barnard.
Later telescopic observations confirmed Io's
distinct reddish-brown polar regions and yellow-white
equatorial band.
Telescopic observations in the mid-20th century
began to hint at Io's unusual nature.
Spectroscopic observations suggested that
Io's surface was devoid of water ice (a substance
found to be plentiful on the other Galilean
satellites).
So as you can see, this wasn't just a discovery
of trying to find the moon, but to try and
understand what it was and what it was like
in regards to its very nature.
Which would be further expanded upon in the
future via attempts to explore the moon with
probes and satellites.
7.
The Exploration of Io Part 1
In the late 1960s, a concept known as the
Planetary Grand Tour was developed in the
United States by NASA and the Jet Propulsion
Laboratory (JPL).
It would allow a single spacecraft to travel
past the asteroid belt and onto each of the
outer planets, including Jupiter, if the mission
was launched in 1976 or 1977.
However, there was uncertainty over whether
a spacecraft could survive passage through
the asteroid belt, where micrometeoroids could
cause it physical damage, or the intense Jovian
magnetosphere, where charged particles could
harm sensitive electronics.
To resolve these questions before sending
the more ambitious Voyager missions, NASA
and the Ames Research Center launched a pair
of twin probes, Pioneer 10 and Pioneer 11
on March 3, 1972 and April 6, 1973, respectively,
on the first unmanned mission to the outer
Solar System.
Pioneer 10 became the first spacecraft to
reach the Jupiter system on December 3, 1973.
It passed within 357,000 km (222,000 mi) of
Io.
During Pioneer 10's fly-by of Io, the spacecraft
performed a radio occultation experiment by
transmitting an S-band signal as Io passed
between it and Earth.
A slight attenuation of the signal before
and after the occultation showed that Io had
an ionosphere, suggesting the presence of
a thin atmosphere with a pressure of 1.0 × 10−7
bar, though the composition was not determined.
This was the second atmosphere to be discovered
around a moon of an outer planet, after Saturn's
moon Titan.
Close-up images using Pioneer's Imaging Photopolarimeter
were planned as well, but were lost because
of the high-radiation environment.
Pioneer 10 also discovered a hydrogen ion
torus at the orbit of Io.
Pioneer 11 encountered the Jupiter system
nearly one year later on December 2, 1974,
approaching to within 314,000 km (195,000
mi) of Io.
Pioneer 11 provided the first spacecraft image
of Io, a shot over Io's north polar region
taken from a distance of 470,000 km (290,000
mi).
This low-resolution image revealed dark patches
on Io's surface akin to those hinted at in
maps by Audouin Dollfus.
Observations by both Pioneers revealed that
Jupiter and Io were connected by an electrical
conduit known as the Io flux tube, which consists
of magnetic field lines trending from the
Jupiter's poles to the satellite.
Pioneer 11's closer encounter with Jupiter
allowed the spacecraft to discover Jupiter's
intense radiation belts similar to Earth's
Van Allen Belts.
One of the peaks in charged particle flux
was found near the orbit of Io.
Radio tracking during the encounters of both
Pioneers with Io provided an improved estimate
of the moon's mass.
This was accomplished by analyzing slight
changes in trajectory of the two probes due
to the influence of Io's gravity and calculating
the mass necessary to produce the deviations.
When this estimate was combined with the best
available information on Io's size, Io was
found to have the highest density of the four
Galilean satellites and that the densities
of the four Galilean satellites trended downward
with increasing distance from Jupiter.
The high density of Io (3.5 g/cm3) indicated
that it was composed primarily of silicate
rock rather than water ice.
The Pioneer probes helped increase interest
in Io many-fold.
Scientists would even go and dedicate weeks
to interpreting signals that were sent to
Io to see how the moon would respond.
But this was still only the beginning.
Before we show the next phase of exploration
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6.
The Exploration of Io Part 2
The Pioneer Probes were vital not just for
exploration, but to show NASA and others that
entities such as them could well and truly
go beyond the asteroid belt between Mars and
Jupiter and thus give us access to the outer
realms of the solar system.
Thus, in the late 1970's, another set of probes
were launched.
Ones that would change the history of the
solar system and how we viewed it forever...the
Voyager Probes.
Voyager 1 & 2 were launched in 1977, and they
were the ones to not only reach Io, but to
go and reveal more about the moon in high-definition
imagery that wasn't available via the Pioneer
probes.
On approach to Jupiter in late February and
early March 1979, Voyager imaging scientists
noticed that Io appeared distinct from the
other Galilean satellites.
Its surface was orange in color and marked
by dark spots, which were initially interpreted
as the sites of impact craters.
The data from the Ultraviolet Spectrometer
(UVS) revealed a torus of plasma composed
of sulfur ions at the orbit of Io, but tilted
to match the equator of Jupiter's magnetic
field.
The Low-Energy Charged Particle (LECP) detector
encountered streams of sodium, sulfur, and
oxygen ions prior to entering Jupiter's magnetosphere,
material that the LECP science team suspected
originated from Io.
The images returned during the approach revealed
a strange, multi-colored landscape devoid
of impact craters, unlike the other planetary
surfaces imaged to that point such as the
Moon, Mars, and Mercury.
The highest-resolution images showed a relatively
young surface punctuated by oddly shaped pits
that appeared more akin to volcanic calderas
than to impact craters, mountains taller than
Mount Everest, and features resembling volcanic
lava flows.
The majority of the surface was covered in
smooth, layered plains, with scarps marking
the boundary between different layers.
Even in the highest resolution images, no
impact craters were observed, suggesting that
Io's surface was being regularly renewed by
the present-day volcanic activity.
Voyager 2 would arrive later on and would
help provide interesting data that would lead
to more data about Io's volcanic activity,
including how in just 4 months things had
changed on the surface of the moon compared
to when Voyager 1 was then.
17 years later, the Galileo probe would go
and further these findings and further show
how volcanicly active the moon was.
As well as make many other discoveries about
other Jupiter moons.
5.
Volcanic Moon
The tidal heating produced by Io's forced
orbital eccentricity has made it the most
volcanically active unit in the Solar System,
with hundreds of volcanic centers and extensive
lava flows.
During a major eruption, lava flows tens or
even hundreds of kilometres long can be produced,
consisting mostly of basalt silicate lavas
with either mafic or ultramafic (magnesium-rich)
compositions.
As a by-product of this activity, sulfur,
sulfur dioxide gas and silicate pyroclastic
material (like ash) are blown up to 200 km
(120 mi) into space, producing large, umbrella-shaped
plumes, painting the surrounding terrain in
red, black, and white, and providing material
for Io's patchy atmosphere and Jupiter's extensive
magnetosphere.
Io's surface is dotted with volcanic depressions
known as paterae which generally have flat
floors bounded by steep walls.
These features resemble terrestrial calderas,
but it is unknown if they are produced through
collapse over an emptied lava chamber like
their terrestrial cousins.
One hypothesis suggests that these features
are produced through the exhumation of volcanic
sills, and the overlying material is either
blasted out or integrated into the sill.
But it's clear if that theory is true.
The discovery of plumes at the volcanoes Pele
and Loki were the first sign that Io is geologically
active.
These plumes form red (from the short-chain
sulfur) and black (from the silicate pyroclastics)
deposits on the surface.
4.
Orbit And Rotation
Although Io always points the same side toward
Jupiter in its orbit around the giant planet,
the large moons Europa and Ganymede perturb
Io's orbit into an irregularly elliptical
one.
Thus, in its widely varying distances from
Jupiter, Io is subjected to tremendous tidal
forces.
These forces cause Io's surface to bulge up
and down (or in and out) by as much as 330
feet (100 meters).
Compare these tides on Io's solid surface
to the tides on Earth's oceans.
On Earth, in the place where tides are highest,
the difference between low and high tides
is only 60 feet (18 meters), and this is for
water, not solid ground.
Io's orbit, keeping it at more or less a cozy
262,000 miles (422,000 kilometers) from Jupiter,
cuts across the planet's powerful magnetic
lines of force, thus turning Io into a electric
generator.
Io can develop 400,000 volts across itself
and create an electric current of 3 million
amperes.
This current takes the path of least resistance
along Jupiter's magnetic field lines to the
planet's surface, creating lightning in Jupiter's
upper atmosphere.
3.
Pop Culture
We’re still getting to know Io as a whole,
though it’s powerful volcanoes have captured
imaginations since their discovery decades
ago.
Io plays a memorable role in the sequel to
2001: A Space Odyssey—2010—in which astronauts
make a dangerous spacewalk above Io’s volcanoes
to board an abandoned spacecraft.
In the show Babylon 5, frequent references
to Io are made as the Earth has a base there
and they use it to help scan for potential
threats to Earth.
2.
Atmosphere
Because of the volcanic activity, Io's atmosphere
contains mostly sulphur dioxide.
Io's orbit cuts across Jupiter's powerful
magnetic lines of force, turning Io into an
electric generator.
As Jupiter rotates, the magnetic forces strip
away about a ton of Io's material every second.
The material becomes ionized and forms a doughnut-shaped
cloud of radiation called a plasma torus.
Some of the ions are pulled into Jupiter's
upper atmosphere and create auroras.
An example of this activity was spotted by
the Hubble Space Telescope, which revealed
the influences of Io and another Jovian moon,
Ganymede, in Jupiter's auroras in 2018.
Io also has a collapsible atmosphere, according
to observations from the Gemini North telescope
in Hawaii and the Texas Echelon Cross Echelle
Spectrograph (TEXES) released in 2018.
The sulfur dioxide envelope of gas freezes
up while Io is in the shadow of Jupiter every
day.
When Io comes back into sunlight, the freezing
sulfur dioxide converts to gas once more.
Scientists long suspected this phenomenon
exists, but it was only after this new study
— which saw Io's atmosphere in the dark
for the first time — that researchers confirmed
it.
1.
Future Exploration
As you can see, we clearly have done a LOT
of research and spent a lot of time exploring
Io.
Its volcanic activity is a source of wonder
and mystery in many respects.
As such, scientists and astronomers are still
hoping to go and explore Io more over the
next many years.
In fact, there are plans right now to send
more probes either to Io directly or to Jupiter
as a whole in order to study the moons more.
Plus, if we were to go and set up a base on
Mars like many hope, it would give us a much
easier place to not just observe the moons,
but also to launch probes and instruments
to study them.
Only time will tell though when our next best
look at Io will be.
Thanks for watching!
What did you think of this look at Io and
the wonders behind it?
Do you understand now why many people are
fascinated by this erupting moon?
What else do you think we will learn from
it via future explorations?
Let us know in the comments below, be sure
to subscribe, and I'll see you next time on
the channel!
