Europa, one of the most exciting moons in the entire solar system.
It is a beautiful world, filled with mysteries.
This is the first ever close-up image of Europa, taken by the Pioneer probe back in 1973.
Since then, we've had the Voyager and Galileo probes explore the moon, and with each visit,
Europa has never failed to surprise us.
We are yet to solve a lot of Europa’s puzzles, but there are many we are starting to piece
together.
I’m Alex McColgan, and you’re watching Astrum, stick with me in this video and together
we will explore some of those fascinating mysteries, and delve into almost everything
there is to know about this intriguing world.
Let’s first of all see where Europa fits into the Jovian system.
Europa is the second and smallest of the four Galilean moons, although it’s still the
sixth biggest moon in the entire solar system, just behind Earth’s Moon, with a diameter
of about 3,000 km.
It takes Europa 3.5 days to orbit Jupiter once.
Interestingly, the first three Galilean moons Io, Europa and Ganymede are locked in a 4:2:1
orbital resonance, due to their gravitational influence with each other.
This means that every time Ganymede orbits Jupiter once, Europa orbits twice, and Io
orbits four times.
This orbital resonance and the constant gravitational tugging from the other moons keeps the orbit
of Europa from ever becoming completely circular.
Due to Europa’s slight elliptical orbit, the magnitude of the gravitational force acting
on it from Jupiter increases and decreases as it orbits.
This creates tides that stretch the moon’s surface.
These forces are significant, as they have a big influence on the moon’s appearance
and what goes on under its surface.
Europa’s surface is made predominantly of water-ice.
As you can tell, it looks very remarkable and distinctive due to these long, continuous
fractures and cracks.
These are called Lineae, which translates to ‘lines’ in Latin.
These lineae are often only about 1-2 kilometres wide but can extend for thousands of kilometres
across the moon’s surface.
We aren’t sure about how or why these lineae are formed at present.
But the most likely theory is that as the crust pulls apart from tidal flexing, warmer
material from beneath fills the gap, in a similar fashion to the ocean ridges on Earth.
In this image taken by the Galileo spacecraft, you will notice some dark brown spots.
They are very small, only about 10 km across, and they are known as lenticulae.
They are also believed to be formed by the upwelling of hot, less dense material to the
surface, either by pushing the existing crust up, or by breaking through altogether.
Should the underground material have broken through, what we can then see are these strange,
unusual terrains, called chaos terrains.
They are really rough patches surrounded by a rather smooth surface.
These spots are expected to be soft and may contain significant information about what’s
under Europa’s surface, which we will get to later in the video.
Data from Galileo also indicated that Europa's equator may be covered in icy spikes called
Penitentes.
These vertical cracks may be up to 15 meters high and will have formed from direct overhead
sunlight on the equator.
Interestingly, penitentes are found on Earth too, in dry regions at high altitudes, although
nowhere near as large as on Europa.
Despite being roughly the age of the solar system, Europa barely has any craters.
Europa has less than 50 major craters, whereas the Earth's Moon has more than 5000 craters
with a diameter above 25 km.
This indicates that Europa’s surface is constantly changing and reforming.
Models suggest that Europa’s surface is only about 30-180 million years old, which
is very young in geological terms.
Additionally, Europa’s icy surface is the smoothest of any known solid celestial object
in the entire Solar System.
Its icy crust also has an albedo or light reflectivity of 0.64, one of the highest of
all moons.
Europa’s albedo makes it 5 times brighter than our Moon.
This surface is bombarded by a constant and intense blast of radiation from Jupiter.
The radiation level at the surface of Europa is equivalent to a dose of about 5400 mSv
per day.
Exposure to radiation at that level would be enough to kill a human in a single day.
The reddish-brown colour spread across the cracks and fractures of the moon is believed
to be due to salt and sulphur compounds mixing with water ice and modified by Jupiter’s
radiation.
A recent study from JPL suggests that Europa might even glow in the dark.
Energetic ions from the radiation penetrates the surface, which would energize the molecules
beneath, which would make them release energy as visible light.
Unfortunately, we cannot see Europa’s dark side from Earth, as we are between it and
the Sun always, so we are going to have to wait for the future missions to Europa before
we can prove this.
Radiation received from Jupiter plays a significant role in Europa's atmosphere as well.
Europa has a very tenuous atmosphere, composed primarily of oxygen.
Unlike on Earth, the oxygen on Europa is formed by radiolysis, or in other words, the process
of radiation bombarding the water ice surface, separating the H2O into oxygen and hydrogen.
Hydrogen escapes Europa’s gravity altogether because it is so light, whereas a lot of the
heavier molecular oxygen remains.
The hydrogen and oxygen that escape Europa’s gravity form a disperse neutral cloud, which
follows the orbit of Europa around Jupiter.
In 2012, the Hubble Space Telescope discovered plumes of water vapour erupting from near
Europa’s south pole.
This image suggests that the water plumes rise up to 200 kilometres from its surface.
In 2018, astronomers found additional evidence of water plume activity on Europa, when they
looked back at the old Galileo data with a new data analysis technique.
A dedicated mission studying these plumes can also help us understand what’s inside
the moon without having to land on it.
Because what may lie underneath that solid ice surface is perhaps the most fascinating
thing about Europa.
There is likely to be a global ocean between a rocky mantle and the water ice crust.
The first clue that this amazing ocean world was hidden under its surface was provided
by the Voyager and Galileo probes in 1979 and the late 1990s respectively.
Between these missions, there was a drastic change in the magnetic field of the moon,
which is not possible unless there is some electrically conductive fluid beneath the
surface.
Europa’s crust also indicates the presence of a liquid layer beneath it, as it rotates
with at angle of 80°, which is not possible if the crust and rocky mantle were mechanically
attached.
Instead, it is likely that the icy crust floats on the ocean and it is believed to make one
full rotation around the moon once every 12,000 years.
The fact that this ocean is not attached also explains the multitude of lineae on the surface.
Tidal flexing should cause lineae to form at specific points on Europa, not all over.
However, because the position of the crust changes over time, and one spot never stays
in place for very long, hence why more and more lineae form.
Europa is 780 million kilometres away from the sun, which is 5 times further away than
the Earth, that makes the sunlight about 25 times fainter here.
As such, Europa, or any other moon in the Jovian system for that matter, barely receives
any heat from the Sun.
So unsurprisingly, it’s cold enough here that the surface is frozen.
In fact, Europa's surface temperature averages about −160 °C at the equator and −220
°C at the poles, keeping Europa's icy crust as hard as granite.
However, tidal pressures exerted on the moon as it orbits Jupiter heats Europa’s core,
so geothermal activity from the core should keep the subsurface ocean in a liquid state.
This ocean is believed to be under only 15 to 25 kilometres of solid, frozen crust.
The ocean itself is probably about 60 to 150 kilometres deep.
Interestingly, Europa is only one-fourth the diameter of Earth, although it may contain
twice as much water as all of Earth’s oceans combined.
What’s most interesting about Europa’s ocean is that scientists believe that it is
in contact with Europa’s silicate rocky mantle.
This makes Europa’s ocean a suitable environment for life as we know it to exist.
We believe that life requires water, minerals and energy to form.
And Europa seems to have all these requirements.
From the evidence we’ve seen so far, scientists are extremely confident that this ocean not
only exists, but that chemical reactions can take place there, and that there is enough
tidal energy heating the core that geothermal activity may exist on this oceans floor.
As we have seen on Earth, whole ecosystems can exist in such places, far away from the
Sun’s light.
So, for now, Europa is one of the most likely places we can find life outside of Earth.
Now, NASA’s Europa Clipper spacecraft is scheduled to launch in 2022 and is likely
to reach the moon by the end of the decade.
It is scheduled to perform more than 42 flybys of Europa.
ESA is also working on their own spacecraft called JUICE (Jupiter Icy moons Explorer),
which will explore Jupiter and three of its largest moons, Ganymede, Callisto and Europa.
JUICE is also scheduled to launch in 2022 and is also likely to reach the moon by the
end of the decade.
These probes are specifically designed to examine Europa's water plumes and atmosphere.
NASA is also planning a Europa lander mission, but this mission is going to launch well after
the Europa Clipper mission.
These missions will help us know more about Europa, and hopefully confirm the answer to
the most tantalising question of all, does it and can it sustain life?
At the very least, these missions will give us a new perspective of our Solar System and
help us understand how it works.
So, there we have it, almost everything you could want to know about the fascinating world of Europa.
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Thanks for watching!
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