We have long considered Mars as a potential second home. But the deeper we study our solar system,
the more new candidates emerge, some of them perhaps even better for colonization.
Life on Earth in its early stages was radically different from what it is today. The atmosphere
was different, completely alien species dominated, and if we were to look at the
landscapes that existed back then, we wouldn’t recognize Earth as it is today.
So perhaps, while we are hunting for potentially habitable celestial bodies,
we should expand our criteria and contemplate the conditions that would foster the existence
of alien life forms. And there’s one world in our solar system that could fit these criteria.
How is Titan the representation of the early Earth? What are these mysterious
deserts on Saturn's largest moon, and what causes its lakes to erupt?
[LOGO]
Titan [Diameter: 3,200 miles / 5,150 km], the largest of Saturn’s 146 moons,
is even bigger than Mercury. But it’s no ordinary satellite. The gigantic
moon is so similar to Earth, it’s almost hard to believe.
Not only does Titan have lakes, seas, and rivers, but it also hides a subsurface
ocean of water, 50 miles [80 km] below the icy ground. In the moon’s skies, there are clouds,
on its surface – organics. It rains on Titan, liquid bodies replenish lakes and seas,
and then evaporate, launching an Earth-like hydrological cycle.
The atmosphere of nitrogen and methane that envelops the satellite is thick enough for
you to safely stroll around its surface without a pressure suit. But that’s only
if Titan wasn’t as cold as -290°F / -179°C and had an oxygen-nitrogen atmosphere like
the Earth. And if you had wings attached to your suit, you could even fly as the moon’s gravity
is just 14% of the Earth’s. Because of this, you would also witness rain falling in slow-motion,
about 6 times slower compared to Earth. Although it would be no ordinary rain. On Titan, it rains
liquid methane, and its droplets are roughly 50% larger than raindrops we see on our planet.
Titan is located some 750 million miles [1,200,000,000 km] from Earth, where it revolves
around Saturn in about 16 days. Titan is tidally locked to the sixth planet. But even though
one of its sides is always facing Saturn, the satellite still has intricate weather patterns.
Saturn’s largest moon receives 100 times less solar energy than our planet,
and it has a thick atmosphere extending 10 times higher into space. In these conditions,
not much light can get through and reach the surface.
For the first half of Titan’s day, which is equivalent to 16 Earth days,
its surface is bathed in a faint orange haze. Looking through this haze would be
like trying to see beyond thick fire smoke. The skies during this part of
the day could be 100-1000 times dimmer than here on our planet in an afternoon. And the
other part of the day brings total darkness to the surface. But even if it was bright enough,
you still wouldn’t see Saturn from the surface of Titan because of the haze.
Interestingly, daytime isn’t the brightest part of the moon’s day. According to computer simulations,
the brightest it gets on this mysterious world is during twilight – up to a factor
of 200 compared to daytime. This is something that happens because of
the way light is scattered by the haze particles in the atmosphere.
And since Titan is tidally locked, with a permanent daylit side and nightside,
there’s also a permanent twilight zone – a border in between the two sides called terminator.
Titan, like Earth, experiences eclipses, which can last up to 6 hours. This is like
having a second night in the middle of a day. Of course, you would only notice it if you were on
the side of the Titan facing Saturn. Otherwise, a solar eclipse would happen during nighttime.
Understanding this is important as it tells scientists how much
light Titan’s atmosphere and its surface receives from the Sun,
which dictates what conditions a potential life on Titan would have to live in.
Just recently, the James Webb Space Telescope was able to detect clouds that form in Titan’s
lower atmosphere during late summertime when its surface absorbs more heat. And this means that
the moon has seasonal weather patterns, just like scientists have predicted it.
Titan’s tilt relative to the Sun closely resembles that of Saturn, so both celestial
bodies experience seasons of approximately equal duration, changing about every 7 Earth years.
Although at a slow rate, seasonal shifts bring change in weather on Titan.
When the Earth’s axis is tilted neither away nor toward the Sun,
something interesting happens. Imagine a line that cuts through the north and south poles, dividing
the planet in half. During this time, occurring twice a year, night and day have about the same
length all over the world. This phenomenon is called the equinox, and Titan experiences it too,
although less frequently – about every 15 years. But when this time of the moon’s year comes,
enormous clouds of methane form in its equatorial regions, bringing about severe wind storms.
During summer on Titan, the winds blow stronger. During the Cassini mission,
scientists saw waves on Titan's lakes, and they were unlike any waves here on Earth.
Titan's weak gravity allows these waves to be much bigger, about seven times taller
than waves in the Earth's oceans. But they move more slowly, up to three times slower.
Winds on Titan also fuel powerful dust storms. Something like this happens in
arid areas on Earth too, when big dust clouds form right before storms. The only
other place in the solar system this phenomenon has been detected is Mars.
This is how organics in the form of dust are scattered around on Titan’s surface.
And although downpours are a rare phenomenon on Saturn’s largest moon,
when they do happen, they leave behind a fascinating footprint. Titan’s rains
are heavy and have a big impact on the surface. They create something called
"alluvial fans." These features are a bit like piles of dirt and rocks shaped like
triangles. They form when water or ice flows and leaves behind the stuff it was carrying.
Scientists have also detected dune fields on Titan taking up to 13% of the moon’s surface.
Compared to sand dunes found on Earth, they are enormous in size – hundreds of miles long,
1.2 miles [2 km] wide, and 330 feet [100 m] high. There’s more sand on Titan than anywhere
else we know of, although this sand isn’t made of silicates like it is on our planet. Instead,
it consists of solid hydrocarbons that fall like rain from the atmosphere.
On Earth, we understand how landforms are created through a straightforward process:
rocks break down into tiny grains, wind carries these grains to specific areas,
they pile up, and eventually, they shape the land. But on Saturn's largest moon,
things are more puzzling. The origin of its landforms has been a mystery because
the sand grains on Titan are quite different from those on Earth. They're weaker and thought to be
more temporary. However, despite this, we've observed long-lasting sand dunes on Titan.
When the wind transports sand grains, they should collide with each other and the surface,
which usually makes them smaller over time. So how do these grains manage to
stick around long enough to form significant landforms?
After studying Titan's landscape, scientists discovered something fascinating. It turns
out that the moon has a special type of sedimentary process known as "sintering",
where neighboring grains smash together and fuse into larger,
stronger pieces that are less likely to be blown away by the wind.
If sand on Titan can adapt in such a way to form complex landforms,
could life have adapted similarly?
There are a lot of similarities between our home planet and this alien faraway world.
The problem with Titan is, its ingredients seem to be all wrong. What’s water on Earth,
is liquid methane and ethane there, including its clouds, rivers, lakes, and seas.
But one thing is certain – this celestial body is still active.
Even liquids flowing on the surface of Titan involve complex physical processes. Similar
to water bodies on our planet, methane lakes on Titan can stratify, that is, create layers
depending on density difference. And not only that, but the liquefied methane and ethane
lakes could potentially erupt. This happens due to the combination of methane, ethane, and nitrogen,
resulting in bubbles powerful enough to shape river deltas within the moon’s liquid bodies.
Understanding how bubbles form in Titan's lakes helps scientists explore how liquids
behave on this intriguing moon. Imagine if a submarine were sent to explore Titan's lakes
one day. If it gives off heat, it could actually cause an explosion of bubbles,
just like the ones scientists have discovered. So, these findings not only tell us about Titan but
also hint at some surprising challenges a future spacecraft might encounter in those alien waters.
Whatever life forms could potentially exist there, they would have a completely different biology,
and so they would look and act like nothing we’ve ever seen before.
According to a team of researchers from Cornell University,
it is possible for cell membranes to form in the conditions present on Titan right now.
On Earth, cell membranes are made up of special molecules called phospholipids.
Imagine these molecules as having a head and a tail. The head is a bit like a magnet,
with a positive and negative side. The tail is neutral, meaning it has no magnetic quality.
Imagine these molecules in water like a sandwich with two slices of bread. The
heads of the molecules are like the outer sides of the bread, and they really like the water,
so they face outward. But the tails of the molecules are like the inside of the bread,
and they want to stay away from the water, so they hide in the middle. This
arrangement makes the membrane flexible – something that is crucial for life.
If there's any form of life on Titan, it would probably need to have a similar
membrane. The problem is, methane has an even distribution of electrical charges,
so Titan doesn't have the right conditions to make these Earth-like membranes. Because of this,
life on Titan would have to find a different way to build its "cell walls."
But scientists have been able to create inside-out membranes in such non-polar
liquids in a laboratory. And they believe that Titanian cell membranes would have a
similar structure. Although they would have to be composed of something else, as liquids
on Saturn’s largest moon probably lack phosphorus and oxygen, and are too frigid for phospholipids.
So what kind of a molecule could this be?
Although the Titanian atmosphere is mostly made of methane and nitrogen, it has traces of different
compounds as well. Computer models have shown that a substance called “acrylonitrile” would be able
to form cell membranes in non-polar liquid methane on Titan. The Cassini mission has previously
detected small amounts of acrylonitrile in the moon’s atmosphere, about 10 parts per million.
Even though there’s a vast difference in temperature in which Earth-like membranes
form and Titanian membranes could form, they both share surprisingly similar qualities,
like stability and internal resistance to external force. So it’s possible for
membranes to form in frigid temperatures of Titan’s lakes, and survive there.
The possibility of methane-based life would change our entire outlook. Instead of focusing solely on
planets in the "habitable zone" of stars, where conditions are Earth-like, we'd also explore
worlds farther from their stars where methane can exist as a liquid. Within our galaxy alone,
the number of potential places to find alien life forms would skyrocket. And if life, on some of
these worlds, has persisted for long enough to develop into complex organisms, we might find
a living counterpart of an imaginary creature, like those mentioned in fantasy movies and books.
But even if, at this stage of Titan’s history, life cannot survive on its surface, there’s a
subsurface ocean of liquid water hiding beneath the moon’s icy coating. Scientists are trying to
find out if organics can penetrate through this ice shell into the ocean. If this is something
that happens on Titan, then this subsurface water could be potentially habitable. Although we still
don’t know much, like what the density or the composition of this global ocean is,
its temperature, and how it interacts with the icy crust above. Another big question is whether
there’s a source of chemical energy down there to allow for metabolism. But one bacterium with
a rare metabolism that’s been found on Earth could potentially live in the Titan’s subsurface ocean.
Billions of years ago, the Earth had a very different atmosphere with high
amounts of nitrogen, CO2, and water vapor, which descended to the surface,
launching a life cycle. The building blocks of life on our planet may have once been the same
ingredients we see today on Titan. In a way, Saturn’s largest satellite is a real-life lab
where astrobiologists can study how these ingredients might have played a role in
the beginnings of life on Earth. Perhaps, some millions or billions of years into the future,
the moon will evolve into a habitable world, teeming with Earth-like organisms.
Soon, we may find out the answer to these questions. Planned to be launched in June 2027,
NASA’s Dragonfly robotic helicopter will search for water or hydrocarbon
biosignatures potentially present on Saturn’s gigantic satellite. With Dragonfly's arrival,
scientists hope to uncover clues about Titan's subsurface ocean, its potential habitability,
and whether the ingredients for life might indeed be present in this distant world.
If we discover signs of alien life on Titan, what might these otherworldly
creatures look like? Share your thoughts in the comments below,
and stay tuned here for the thrilling discoveries that await us in space. Thanks for watching!