Thanks to Geologie for sponsoring today’s video.
I think most of us know what the planets look like in the visible light spectrum.
Saturn’s pale, golden colour, Jupiter’s red bands and colourful clouds, and Neptune’s
dark blue hue.
However, light is emitted or reflected by planets in wavelengths beyond our eye’s
capabilities, like infrareds and ultraviolets, and often what we can see in these wavelengths
is actually far more valuable to scientists than simply how a planet would appear to the
natural eye.
That’s because certain things that are invisible to our eyes may be very visible in infrared
or ultraviolet, or vice versa.
And if we want to know what substances are found on a planet, the electromagnetic spectrum
can help us again.
I’m Alex McColgan, and you’re watching Astrum, and in this video, I want to focus
on what we’ve seen through more of the electromagnetic spectrum on Jupiter and some of its moons,
and how this different approach may give you a new perspective on the largest planet in
our solar system.
Just as a point of comparison, let’s first look at how Jupiter appears in natural light.
The various spacecrafts that have passed Jupiter have revealed it to be a beautiful planet.
You will immediately see a lot of the main cloud deck of Jupiter in visible light.
These are not water clouds, like on Earth, but rather ammonia ice clouds.
If you look closely, you can start to perceive the different altitudes of these clouds.
The dark narrow regions are actually shadows cast by the tall, lighter coloured clouds.
It seems like the higher in altitude these clouds are, the lighter they become, which
can be seen in the highest altitude pop-up clouds in this region, which are a snowy white.
The process behind the different colours in Jupiter’s atmosphere isn’t completely
understood, but it’s believed to be caused by the upwelling of compounds that originated
deep within Jupiter suddenly being exposed to the UV radiation from the Sun.
As they lift up to the highest altitudes in Jupiter’s atmosphere, these compounds begin
to darken, eventually sinking back down again into the lower altitudes.
But as you can see, Jupiter’s ammonia cloud deck is opaque, we can’t see through it.
If visible light was the only wavelength of light we could work with, the vast majority
of Jupiter would remain a complete mystery.
Luckily, we also have instruments that that can see beyond our eye’s capabilities.
And in certain wavelengths in the infrared, we can see Jupiter in a completely new light.
Perhaps the most striking is to observe Jupiter using the 4.68 μm wavelength, as this shows
the heat of the planet.
Very interesting, in this view taken by the Gemini Observatory, it is the lower altitude,
reddish bands that are the brightest.
You see, Jupiter actually emits more heat than it receives from the Sun.
It is contracting in size, which heats it up.
This heat eventually makes its way out of the planet through the cloud deck.
The heat escapes easiest where the cloud deck is thinnest, which is why features like the
Great Red Spot and the white bands in visible light are dark is this image.
Luckily, we aren’t just limited to a disk view of Jupiter either - thanks to the Juno
spacecraft that is in orbit around Jupiter right now.
Viewing Jupiter’s poles in infrared again, scientists were able to create a 3D map of
the incredible vortices that are found there.
Jupiter’s north pole has 9 seemingly constant vortices, 8 in a square shape revolving around
a large one found right in the centre.
Again, you’ll notice that it is the lowest altitude regions that are emitting the most
heat.
Because this wavelength only reveals heat, the haze and shadows in the atmosphere don’t
block the view as much as you would get in visible light, meaning it can give us an unprecedented
view of the 3D structure of these vortices.
It’s still pretty cool here for Earth standards, even the yellow sections are only -13°c,
with the darker, higher altitude regions being -83°c.
And because the heat is coming from Jupiter itself, this view is available to Juno night
or day, it isn’t reliant on reflected sunlight.
Storms can show up in infrared before they are noticed in visible light too.
Look at this comparison taken by Hubble.
These near-Earth sized storms located beneath the cloud tops are much warmer than the ambient
surroundings, indicating that internal heat does play a big role in generating atmospheric
disturbances.
And while we’re on this wavelength, let’s also have a quick look at Jupiter’s volcano
moon, Io.
Unsurprisingly, Io’s nightside is totally lit up by the volcanic activity on its surface,
making it very easy to identify new volcanoes, and to keep track of the ones we already knew
about.
Juno has had several looks at Io, each one revealing it to be a hive of activity.
A truly hellish yet intriguing world.
In fact, all of the Galilean moons have been examined in infrared but using specific wavelengths
which can reveal different things.
For instance, here is the Galileo probes infrared view of Europa in the 1.5-micron water band.
When viewing an object through this particular wavelength, we can see locations where water
is present.
The deep blues in the image are the locations of the purest water ice, whereas other colours
indicate a mixture of water ice with other minerals.
This is called spectroscopy, where you can ascertain what molecules are on a planet without
actually having to land there.
You see, when white light reflects off a certain atom or molecule, that molecule will absorb
a band of light and reflect the rest.
If we analyse the missing light band, we can know what the molecule is.
So, think of this image less as a photo, but rather as a graph of data, indicating locations
of certain molecules, colours arbitrarily chosen by a scientist to represent the data.
For instance, if we look at this image showing the absorption band for sulphuric acid, it
is the brighter regions this time that show where the abundance of sulphuric acid on Europa
is.
This abundance is found around the surface’s cracks – so it may come from the ocean below
the crust – but it’s also found on the trailing side of Europa seen on the top left
of the image.
It seems that as Europa orbits, it is bombarded by sulphur ions.
Incredibly, this sulphur probably originated from the eruptions of Io’s volcanoes.
If we look at a crater on Callisto, infrared data has been overlayed onto a visible light
image.
Reds indicate more water ice, blues show less.
This is pretty interesting, as this is one of the highest resolution infrared images
we have of a body around Jupiter, this image only being 200km across.
It adds a lot of information you wouldn’t get from the visible light image, namely,
there’s a concentration of water in the crater, but a ring directly around it where
no water is present, and then water appears again in this ray system coming away from
the crater.
The icier regions come from the impactor exposing the ice beneath the surface, but why there’s
this ring between the centre crater and the debris from the ray system is a bit of a mystery.
Perhaps the icy debris from the impact didn’t start hitting the ground until it reached
this distance out.
In any case, this image shows that non-ice materials only make up a thin layer on the
top of the surface of Callisto.
And what does Jupiter look like through certain bands of infrared?
This image is really interesting, the top left and right images are taken in 1.61 and
2.73 microns respectively.
In these bands, we can see the cloud deck similarly to what we can see in visible light.
However, in the middle, we are looking only through 2.17 microns, the absorption band
of hydrogen.
As we know, Jupiter is predominantly hydrogen, meaning the hydrogen in the atmosphere suddenly
becomes opaque and visible at this wavelength.
In fact, the only features still visible are the really high-altitude clouds, the ones
that poke through most of the hydrogen in the atmosphere.
The bottom left image is the 3.01-micron band, where there is some absorption, but not as
much.
At this band, it is methane and ammonia that are absorbing the light.
Bottom middle is at 4.99 microns, giving us another heat map, and bottom right is a false
colour combination of all 5 images, which is what you see happening if ever I show a
false colour image in one of my videos.
Now you know what these false colour images are trying to show!
The last interesting view of Jupiter I want to show is in the ultraviolet.
Absorption spectroscopy in the ultraviolet isn’t super useful in planetary astronomy,
the only time I can think of it being actively used on Jupiter was to track the impact of
Comet Shoemaker-Levy 9 back in 1994.
There, the dust absorbed a lot of the UV sunlight and so scientists could easily track winds
in the planet’s stratosphere by watching the evolution of these features.
However, molecules that are hot enough will emit light in lots of different wavelengths.
And there is a bright source of light coming from Jupiter in ultraviolet and infrared,
its auroras.
Jupiter’s auroras are extremely powerful compared to the ones on Earth, and are a permanent
feature on the planet.
Hubble, which can see in ultraviolet, has been tracking Jupiter’s auroras for years,
although the best views have come from Juno in the infrared, simply due to Juno’s orbit
taking it over the planet’s poles, whereas Hubble’s viewing angle makes observations
difficult.
These auroras are strongly influenced by the magnetic field environment of Jupiter streaming
charged particles into its upper atmosphere, plus from the flux tubes between it and its
moons.
So, there we have it.
A look at Jupiter in a very different way than what you may be used to.
And as you can see, absorptions and fluorescence through spectroscopy can help us understand
a planet far more than what only visible light can reveal.
We can determine molecules and minerals, observe a planet’s heat map, and view aurora interacting
with the planet’s magnetosphere.
Everything together helps us get a more complete picture of how a planet works, and why it
behaves the way it does.
Want more videos about this for the other planets?
Let me know in the comments below.
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