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.
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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!