Orbiting the magnificent gas giant planet Jupiter, is the mysterious icy moon,
Europa, a seemingly frozen world about the same size as our Moon.
With a surface temperature of about -160 degrees Celsius (-256 degrees Fahrenheit) and
a location that means it has to withstand a relentless pummelling of radiation.
At first sight, it would be easy to think of Europa as a barren,
ball of ice. But despite the harsh conditions it exists within,
this fractured moon is one of the most promising places to search for alien life.
So how could life survive on such an extreme moon? And if it does exist, what might it look like?
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Many spacecraft have passed by Europa during their missions,
but it was NASA's Galileo spacecraft that elevated our understanding of this icy moon to a new level.
It discovered the first solid evidence that an enormous ocean exists beneath its surface.
An ocean with possibly two or three times as much water as all of Earth's combined.
Arriving at the Jovian system in December 1995 with the aim of exploring Jupiter and its large
moons, Galileo passed by Europa multiple times, coming as close as 201 kilometres. (125 miles)
It captured its frozen terrain in incredible detail, allowing
us to see close-ups of its cracks, ridges and jumbled-up landscape. But
also find intriguing evidence of what might be happening below its crust.
Galileo confirmed that Europa was geologically active. Its close-up
images revealed the enormous cracks in the moon's surface had separated,
and dark, icy material had flowed into the opened gaps.
As with the spacecraft that came before it,
Galileo also found only a handful of impact craters, which are expected to
build up over time as the surface is constantly bombarded by meteorites over billions of years.
Much like our own Moon for example. But Europa is smooth, suggesting that its surface
is relatively young and that something had erased any large craters. Such as icy, volcanic flows.
One of the most important measurements made by the Galileo mission, however,
showed how Jupiter's magnetic field was disrupted in the space around Europa.
This measurement strongly implied that a special type of magnetic field is
being created within the icy moon by a deep layer of some electrically conductive fluid.
Based on Europa's icy composition, scientists think the most likely material
to create this magnetic signature is a global ocean of salty water.
There are even images from the Hubble Space Telescope that appear
to show huge plumes of water vapour erupting from Europa’s south pole,
although, unfortunately, they are not high-resolution enough to be definitive.
But if Europa's surface is frozen solid, then how could a massive ocean of salty water form? And, if
there is liquid water down there, could life have really started in such a bizarre environment?
While the icy shell of Europa is clearly frozen as hard as a rock,
the interior is warmer because it is heated by what's called tidal flexing.
The side of Europa that’s closest to Jupiter experiences a stronger pull than the other side,
stretching the entire moon back and forth, probably causing the long cracks that
run across its icy surface as well as heating the interior through friction.
Similar to how repeatedly bending a paperclip generates heat for example. It is this constant
flexing that melts the internal ice and creates Europa's enormous ocean.
But is it really possible for life to start on a
frigid moon hundreds of millions of kilometres away from the Sun?
Well, life as we know it seems to have four main requirements. Liquid water,
certain chemical elements, an energy source and of course, time.
We have already discovered that Europa may have an enormous ocean of liquid water that
is protected below its crust. And certain studies of the ocean have
suggested that it may have formed just a few hundred thousand years after the
moon formed. Which is estimated to be around 4.5 billion years old.
Giving life, if it does exist there, plenty of time to get going.
But what about the other two requirements? Chemical elements and an energy source.
Chemical elements are the building blocks of life as we know it and they include carbon,
hydrogen, nitrogen, oxygen, phosphorus and sulfur.
These elements are common throughout the universe and makeup 98% of living
matter on Earth by combining to form organic molecules essential to life.
Scientists think these elements were likely present during the formation of Europa
and may have even been added to later on when asteroids and comets collided with the icy moon.
One good example of chemical elements discovered on Europa was made fairly
recently when the James Webb space telescope detected large amounts of
carbon dioxide on its surface as can be seen in this incredible infrared image.
Europa is shown as blue while the carbon is white and it is thought
that it likely originated from the ocean below.
Then we need an energy source. All life as we know it requires it to survive. Here on Earth,
life relies mainly on the Sun for energy, such as through photosynthesis.
Plants convert sunlight into energy,
allowing them to grow and that energy is then transferred to those who eat the plants.
But any life that may exist in the ocean of Europa is hidden below the thick ice,
no light can penetrate through it, meaning that a process like photosynthesis couldn't
work. Instead, life would have to be powered purely by chemical reactions.
And these reactions could come in multiple ways, such as from Jupiter's powerful radiation perhaps
that is bombarding Europa's surface. Or more likely from the warm rock on the sea floor.
As the icy moon orbits around Jupiter, its interior flexes as we have already
discovered. The flexing forces energy into the moon’s interior,
which then seeps out as heat. The more the moon’s interior flexes, the more heat is generated.
If Europa’s rocky ocean floor is heated by tidal flexing, that process could potentially
be supplying energy in the form of available chemical nutrients in hydrothermal vents.
And this type of process can be seen here on Earth where life is abundant.
The vents are like bubbling cauldrons of energy, spewing out super hot water
that has flowed below the Earth's surface, becoming heated by a layer of molten magma.
They erupt with plumes of what looks like smoke bellowing out of a chimney,
but within it is a soup of chemicals that certain life can thrive on.
The chemicals would be toxic to human beings,
but these organisms can convert the chemicals to energy.
This process is called chemosynthesis and is what ultimately powers entire
ecosystems around hydrothermal vents found in the deep dark regions of our
oceans. The places where the Sun's light cannot reach.
The vents are the only places on Earth in fact,
where the ultimate source of energy for life is not sunlight but the Earth itself.
Huge red-tipped tube worms, ghostly fish, strange shrimp with eyes on their backs
and other unique species thrive in these extreme deep ocean ecosystems.
So life as we know it on Europa it seems could be possible, but what might it look like?
To get an idea, one place we could look is within one of the deepest,
darkest points on Earth, the Mariana Trench.
The deepest point in the Mariana Trench is called the Challenger
Deep and is 11 kilometres (7 miles) below sea level. It is difficult to
comprehend how deep that actually is, but if you placed Mount Everest there,
the peak of the mountain would still be more than 2000 metres (6561 feet) below sea level.
However, that's nothing when compared to Europa's ocean, which is anywhere between
60 - 160 kilometres (40 and 100 miles) deep. Despite this enormous difference
in depth, however, the conditions between the two environments may still share some similarities.
Imagine a vast, seemingly endless, pitch black void filled with crushingly cold seawater,
this is the type of oppressive environment life within the Mariana Trench has had to adapt to.
But dive deep enough, and you will find some of the weirdest creatures on Earth,
creatures so strange that you would think they were from Europa.
Take the snail fish for example, a species that breaks the record
for any living vertebrate. It is the deepest living fish ever discovered
found at more than 8000 metres (26246 feet) below sea level.
This weird translucent tadpole-looking fish is known to contain chemicals which
help keep its membranes and cell walls flexible so that the crushing pressure
doesn’t kill them. But there are creatures that live deeper.
Within the deepest region of the Mariana Trench, the challenger deep,
three organisms are most commonly found.
The first are called xenophyophores and are the world's largest living single-celled
organisms that resemble spherical or frilly sponges about 20 centres across (8 inches).
It is unsure exactly how these weird creatures survive, but it is thought
that they produce slime that soaks up microbes from the sediment around them.
Then there are Amphipods, which are shrimplike scavengers that
survive the deep seas because of exoskeletons that contain aluminium.
How these little creatures find this metal is a mystery,
but scientists think they use sugar based chemicals in their guts to extract aluminium
ions from the sea floor as they feed on debris raining down from above.
The third are called holothurians which are a species of deep sea sea cucumber. They
are the most alien of the known animals in this region and are highly diverse,
appearing with spiky, brightly coloured skin or smooth, translucent skin.
Vast fields of sea cucumbers have been discovered at the bottom of the Mariana Trench like cows
grazing over pastures as they feed on bacteria and decomposing matter on the sea floor.
So if life has managed to thrive in the deepest oceans of Earth,
could it have also done the same in the even deeper oceans of Europa?
Until we send a probe capable of drilling through the thick layer of ice that encases it,
we may never know. Europa could be full of alien creatures, or it could be completely barren.
However, that burning question may be answered in the next few years. Because
the European space agency along with NASA each have two separate major missions to Europa.
The first from ESA is called JUICE and has already launched in April 2023, arriving in 2031
for a double flyby with the aim of collecting new data on the chemistry of the icy moon.
Then we have NASA's Europa Clipper, which is a mission designed to determine once
and for all whether this icy moon's ocean is habitable or not. It is
scheduled to launch in October 2024, but won't arrive until April 2030.
The exciting missions should complement each other,
but neither will be able to confirm if aliens exist here,
just whether the icy moon has the right conditions to support life as we know it.
If we did eventually find some form of life on Europa it would
probably be in the form of microbes, surviving around a hydrothermal vent.
But If it can be demonstrated that life formed
independently, regardless of how complex it is, in two places around the same star,
it would then be reasonable to suggest that life springs up fairly easily once the necessary
ingredients are present and that life might be found throughout our galaxy and the universe.
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there is plenty more to come. Thank you for watching. And I'll see you next time.