Earth. A relatively small and
insignificant terrestrial planet in the grand scale of the cosmos. But there is
one feature that makes this world truly special. Looming beneath its protective
atmosphere simple and complex organisms thrive. For billions of years,
evolution has shaped the inhabitants of Earth eventually creating sentient life
capable of grasping the complexities of the universe. Humans have often looked to
the Stars and wondered if we're in fact alone drifting through the vastness of
space. While it appears sentient life is exceedingly rare, is it possible that
simple cellular life is relatively common in the cosmos? We've customarily
limited our search for life to the circumstellar habitable zone, eloquently
called the Goldilocks zone. This is a range of orbits around a star that
provides enough radiant energy to support liquid water on the surface of a
planet, given sufficient atmospheric pressure. Several factors are considered for calculating the habitable zone, the most
important being the size and type of star. Hotter stars will push the
habitable zone further out whereas cooler stars will require planets
orbiting much closer to remain within this zone. For our solar system the inner
edge is around 142 million kilometers from the Sun. The outer edges around 240
million kilometers. That puts Earth barely within the inner edge of the
habitable zone and Mars beyond the outer fringe. Incredibly scientists are
speculating about the existence of life on an exotic world quietly orbiting
through the outer solar system. With a dense planet like atmosphere rich in
nitrogen, weather that produces methane rain, and stable bodies of liquid on the
surface, Saturn's moon Titan is the most unique
and exciting world in our solar system. This orange moon is a frozen, yet
flammable world with hundreds of times more liquid hydrocarbons than all the
known oil and natural gas reserves on Earth. So why are we considering the
existence of life on Titan? After all it's almost one and a half billion
kilometers away from the Sun, well outside of the habitable zone. So far in
fact that sunlight traveling at... well, the speed of light... takes over an hour to
reach Titan. And temperatures on the surface are cold enough to make
Antarctica seem like a tropical paradise. Nevertheless, astonishing discoveries now
suggest that given the right elements, cellular life might thrive in these
frigid conditions. Discovered in 1655 by the Dutch
astronomer Christiaan Huygens, Titan was the first known moon of Saturn and only
the sixth known moon in the solar system after Earth's moon and the Galilean
moons of Jupiter. Huygens named it Saturni Luna, Latin for
Saturn's moon. The name Titan came from John Herschel, the son of William
Herschel who had discovered Mimas and Enceladus. He suggested names of the
mythological Titans brothers and sisters of Chronos, the Greek Saturn. In Greek
mythology, the Titans were a race of powerful deities, descendants of Gaia and
Uranus, that ruled during the legendary Golden Age. Today we know Titan as the
sixth ellipsoidal moon from Saturn and the only moon in our solar system with a
dense atmosphere. Compared to the other major moons of Saturn, Titan truly lives
up to its name Rhea is the closest in size, but it's
still 3 times smaller. Evidence suggests that during the formation of Saturn any
large moons were either absorbed by dramatic collisions or simply ejected
from their orbits while passing too closely to the mighty Titan. Both Rhea
and Iapetus are believed to be the remnants from spectacular collisions
early in Titan's history. Titan's diameter of 5,150 kilometers
is about half the diameter of Earth and nearly as large as Mars, making it the
second largest moon in the solar system after Jupiter's Ganymede. While Titan
appears larger, if we remove the dense atmosphere it's clear Ganymede wins the
size contest. Even Mercury has a diameter smaller than Titan, however
Mercury is denser than both Titan and Ganymede combined. Compared to our own
moon, Titan is 50% larger and 80% more massive. Titan's density is relatively low
for its volume, so it has about 86% less gravity than Earth, which
means you could jump almost eight times higher than you could on earth. Standing
on the surface of Titan you would experience an average temperature of
-179 degrees Celsius. Titan's distance from the Sun yields this
forbidding and persistently frigid environment. A mere one percent of the
sun's illumination reaches Titan. This means mid day would appear extremely dim,
yet it would be 300 times brighter than the illumination observed under a full
moon on earth. Orbiting 1.2 million kilometers from Saturn Titan takes only
16 days to complete one orbit. If you could see through the hazy atmosphere
while standing on the surface, Saturn would appear 11.4 times
larger in the sky compared to our own moon as seen from the surface of Earth.
Titan's orbital eccentricity is rather high, which means its orbit is not very
circular and thus passes closer to Saturn on one side of its orbit.
Like our own moon, Titan is tidally locked in synchronous rotation above
Saturn's equator. This means it always shows the same face towards Saturn and
its day is equal to its orbital period. Composed of half water ice and half
rocky material, Titan has a bulk density of 1.88 grams per centimeter cubed. Its
hydrous silicate core is about 3,400 km in diameter. Surrounding the
core are several layers of different crystalline forms of ice. A liquid
subsurface ocean composed of water and ammonia is found under the crust. This is
possible due to heat and pressure within Titan's interior, and to some extent, tidal
forces from Saturn which combined produces enough heat to sustain liquid
water below its surface. Above the subsurface ocean is a thin water ice
crust. On earth the crust sits on top of the upper mantle which is made up of hot
high-pressure rock that slowly flows over long periods of time causing land
masses to shift as they have since the time of Pangaea. On Titan however, surface
features shifted by 30 km over a period of only two years. This indicates
the crust of Titan is not attached to the interior, instead it actually floats
atop a global ocean. Like Europa and Enceladus, scientists believe the
conditions for life could exist within the subsurface ocean layer. Here on earth
we find life thriving around hydrothermal vents in the deepest parts
of the ocean where no sunlight penetrates, so it's not hard to imagine
that life could be thriving within Titan's subsurface ocean, but that's only one
potential for life on this planet like moon. Titan's thick orange atmosphere is the
most distinguishable feature we can see from space. It's orange color is likely
produced by hetero polymer molecules called tholins. These are tar like,
organic precipitates that are thought to form in reactions resulting from the
sun's photolysis of methane in Titan's nitrogen-rich atmosphere. While tholins are not found on modern-day earth, they are rather abundant on icy moons in
the outer solar system. Evidence suggests that though tholins may facilitate the
formation of prebiotic chemistry. This could have a significant implication of
the origins of life. Composed of 98.4% nitrogen, Titan has the only
nitrogen-rich atmosphere in the solar system aside from earth.
The remaining 1.6% is composed of mostly methane and a little hydrogen. With no oxygen in the atmosphere you wouldn't be able to breathe on titan
though. There are trace amounts of other
hydrocarbons like ethane, acetylene, propane, and other gases such as argon,
helium, and even hydrogen cyanide. Titan's atmosphere is 2 times thicker than
Earth's atmosphere and about 7.3 times more massive on a per surface area basis.
Standing on the surface you'd feel about 50% more pressure than you would on
Earth. That's equivalent to the pressure you'd feel when diving 15 feet
underwater on earth. As a result you would not require a pressure suit to
survive on Titan, but you would need oxygen to breathe, and without an
insulated suit you would freeze where you stood in seconds. Given Titan's thick
atmosphere and low gravity, you could fly like a bird with a set of wings strapped
to your arms. The physical exertion required might be similar to swimming
through water on earth. Surely this knowledge would greatly have
been appreciated for those who attempted such comical feats a century ago on
Earth. Titan's low gravity struggles to retain
its atmosphere that wraps rather loosely around the moon and rotates much faster
than its surface. The mesosphere extends 600 km above the surface. That's
about 2 times higher than the International Space Station orbits Earth
and about 480 km higher than Earth's mesosphere. Like all the moons in
our solar system, Titan lacks a magnetosphere required for shielding its
atmosphere from the solar wind, however Titan spends 95% of its time
within Saturn's magnetosphere. This graphic illustrates Titan just outside
of Saturn's protective magnetosphere for a short period of time during its 16 day
orbit around the gas giant. Both sunlight and Saturn's magnetosphere
are central to the formation of Titan's incredibly thick haze. 1,000 km
above Titan's surface, nitrogen and methane molecules are broken down as
photons and highly energized particles collide with the atmosphere. In a chain
of chemical reactions triggered from positive ions and electrons a multitude
of hydrocarbons are formed. As these compounds grow larger they begin to sink
deeper within Titan's atmosphere due to their increasing weight. Within the lower
atmosphere these large aggregates of atoms and molecules benefit from
favourable conditions ultimately producing carbon-based
aerosols which directly affects Titan's climate. Titan's climate is uniquely regulated by
the presence of conflicting environmental effects. Atmospheric
methane creates a greenhouse effect on the surface, without which Titan would be
far colder. Conversely, carbon-based aerosols that
produce the thick atmospheric haze contributes to an anti greenhouse effect.
This in turn reflects 90% of sunlight back into space canceling a portion of
the greenhouse effect and making its surface significantly colder than its
upper atmosphere. Seasons ebb and flow on Titan, each lasting about
seven-and-a-half earth years. When the Cassini spacecraft arrived at Saturn in
2005, Titan's North Pole was in the middle of winter. By the end of its mission,
Cassini witnessed the seasons change as the North Pole emerged into the light of
spring and the South Pole transitioned into fall. During the seasonal change
scientists discovered a monstrous ice cloud over the South Pole. Interestingly,
this cloud formed in the stratosphere, a stable region high above the troposphere
where the active weather layer is found. Global winds and Titan's stratosphere
transport gases from the pole in the warm hemisphere to the pole in the cold
hemisphere. At the cold pole, the warm air sinks in a process known as subsidence. The sinking gases -- a mixture of smog like
hydrocarbons and nitrogen bearing chemicals called nitriles -- encounter
colder and colder temperatures on the way down. Different gases will condense
at different temperatures resulting in a layering of clouds over a range of
altitudes. At an altitude of 200 km, a noxious ice cloud was also
observed above the South Pole. Experiments determined that the exotic
ice cloud is a combination of hydrogen cyanide and the large ring shaped
chemical benzene. The two chemicals appear to have condensed at the same
time to form ice particles rather than one being layered on top of the other.
Drifting below these exotic cloud formations are methane rain clouds that
form in a remarkably similar way as clouds do on Earth. As liquid methane
evaporates from the surface, clouds are formed when it reaches an altitude where
the combination of temperature and air pressure is right for condensation.
Typically only 1% of Titan is covered by clouds though outburst of rapid cloud
expansion by 8% has occurred. As the clouds accumulate, thick droplets of
liquid methane rain down giving rise to surface features strikingly similar to
Earth. Adorned with mountains, valleys, dunes,
rivers, seas, and lakes, Titan's surface is covered with earth-like features making
it an exciting study among the scientific community. Yet there are
surprisingly bizarre characteristics on its surface. Instead of sand or dirt,
Titan's surface is covered by non silicate granules. The granules are essentially
plastics formed in the atmosphere as hydrocarbons produce longer chain
molecules that fall to the surface. These include propylene, which is found
in common household plastics we use every day. A rather peculiar phenomenon
indicates these granules are electrically charged. Sand dunes on Earth
are shaped in the direction the wind blows, but Titan's dunes are curiously
formed in the opposite direction of the prevailing winds. When strong winds
disturbed the non silicate granules on the surface, an electrostatic charge is
produced as the grains collide with each other. This charge provides enough cohesion that the grains can stick together for months at a time, particularly because of Titan's low gravity. Scientists compare
this to the same effect you might observe with packing peanuts in
shipping boxes. If you've ever stuck your arm in a pile of packing peanuts you
probably noticed that some of them stuck to your arm due to a frictional charge.
The same effect can be observed if you rub a balloon against your hair.
The electrostatic charge lifts your hair up as you pull the balloon away. Unlike
many of the moons in our solar system Titan's surface is relatively smooth with
few impact craters. There's a couple of reasons for this. Firstly, Titan's thick
atmosphere destroys most objects colliding with it before they can ever
reach the surface, and second it's believed geological processes may have
reshaped Titan's surface. Although Titan has been around since the
formation of the solar system four and a half billion years ago, its surface is
much younger. Because Titan is so cold, evidence
suggests that cryovolcanoes are the force reshaping Titan's surface.
Unlike volcanoes on earth that erupt hot magma, these things eject volatiles such
as water, ammonia, or methane -- in a sense these are ice volcanoes and most likely
the source of methane found in Titan's atmosphere. An area of the surface known
as the Xanadu region is a large reflective equatorial area about the
size of Australia. It's filled with hills and cut by valleys and chasms. After
hitching a ride on the Cassini spacecraft the Huygens space probe
landed on the surface of Titan near the Xanadu region on January 14, 2005. Taking
three hours to descend through Titan's thick atmosphere,
Huygens became the first probe to land in the outer solar system and the only
probe to land on a moon other than our own. It sent back data and images for
about 90 minutes after touchdown and remains the most distant landing of any
human-made craft. Although no lakes or oceans were seen from Huygens images, it
appears to have landed in a dried -up lake bed. The rounded stones seen in front of
Huygens camera are strikingly similar to river stones on Earth that are shaped by
flowing water. Scientists believe the landing site is covered by liquid
methane during seasonal rains, but as the seasons change sunlight evaporates the
liquid leading to the dry lakebed seen in these images. Titan also features mountains on its
surface. Radar altimetry suggests height variation is low, typically no more than
150 meters. Occasional elevation changes of 500 meters have been discovered and
Titan has mountains that sometimes reach several hundred meters to more than one
kilometer in height. While stunningly beautiful, mountains are relatively
common. But the incredible discovery of flowing liquid on the surface shatters
any commonality with other worlds besides Earth. H2O. A molecular compound
found in 117 million lakes dotting the surface of every continent on earth, yet this accounts for less than 1% of Earth's water. A whopping 97% is found in
a vast global ocean covering 71% of our planet. Our proximity to the Sun
facilitates these stable bodies of liquid. Water oceans and lakes filled with water
are so familiar to us that Titan challenges our wildest imagination as
the only other home in our solar system to hold stable bodies of liquid on its
surface. But unlike Earth, Titan's lakes and seas are not filled with water.
When the Cassini spacecraft began studying the Saturnian system in 2004, it
observed a dark feature near Titan's South Pole called Ontario Lacus. This was later confirmed to be a hydrocarbon lake
filled with liquid methane, ethane, and propane, the main components found in
natural gas. Ontario Lacus is the largest lake found in Titan's southern
hemisphere. Lacus is of course Latin for lake. Radar measurements indicate the
average depth of Ontario Lacus is extremely shallow, ranging from 40
centimeters to 3 meters, and a maximum depth of 7 meters or about 23 feet. With
methane being an extremely flammable compound in the presence of oxygen, it's
difficult to imagine this stuff lapping against a lakeshore as water does on
Earth. It's certainly a good thing Titan's atmosphere is lacking oxygen. When Titan's
North Pole emerged from 15 years of winter darkness Cassini discovered a
lake called Jingpo Lacus. This stunning photo of the infrared specular
reflection was captured by Cassini as sunlight was reflected off the surface
of the lake. Dozens of smaller lakes have been
discovered in Titan's North Pole region, some of them up to 50 kilometers across.
It seems the lack of sunlight in Titan's polar region prevents this
rather high concentration of lakes from evaporating.
But lakes aren't the only surprise found on Titan's surface. It also has three seas
of liquid methane. Located near the North Pole, Ligeia Mare is the second largest sea on Titan. It's larger than Lake Superior on
Earth with a surface area 126,000 square kilometers and contains enough
liquid methane to fill Lake Michigan three times over.
Ligeia Mare is deeper than Ontario Lacus averaging 20 to 40 meters, with
some parts exceeding 200 meters in depth. Several hydrocarbon rivers flow into
like a Ligeia Mare, the longest one stretching 400 km across the
surface. Radar observations showed the surface of Titan's second largest sea was
smooth as glass with waves no taller than one millimeter. This was a
confounding discovery. Given Titan's atmospheric density, waves can be
generated at lower wind speeds than on Earth, and should be seven times higher
courtesy of Titan's lower gravity. Either the liquid is so viscous that waves
struggle to form, or more likely surface winds were minimal during observations. A
year on Titan is equal to 30 years on Earth, so its seasons are rather long.
It's possible Ligeia Mare is seasonably calm during the long dark winter while
the sun's energy may drive stronger winds during Titan's long summer and thus
produced higher waves. Another rather peculiar phenomenon was observed in Ligeia Mare.
Informally known as Magic Island, observations show the evolution
of a transient feature within the lake. Cassini witnessed this island disappear and
reappear over time, which can't be explained by tides, sea level, or sea
floor changes. We're not sure, but scientists speculate that nitrogen
bubbles formed in Titan's oceans sit on the surface for a period of time
creating a temporary island that eventually dissipates. Titan's largest
sea is also found in the north polar region. The Kraken Mare is 400,000 square
km. That's almost the same size as Texas! Named after the legendary sea
monster, Kraken Mare is split in two parts with a strait connecting each side
that's roughly the same size as the Strait of Gibraltar. Because of Titan's orbital eccentricity it experiences more tidal forces from Saturn as it passes
closest to the planet. This may cause tides of 1 meter generating strong
currents and whirlpools in the strait, affectionately nicknamed the throat of
Kraken. We've only discussed a few of the major lakes and seas on Titan. There's at
least 36 lakes we know of and three seas. Together they contain 300 times the
volume of oil reserves on earth. While Titan's lakes and seas are incredibly
intriguing, the most exciting part is the possibility of life thriving within them. Whether or not life is present on Titan
is one of the most intriguing questions currently being researched by scientists.
Titan's thick atmosphere is a soup of complex organic compounds ideal for
prebiotic chemistry or potentially exotic life. Critics assert that Titan is
far too cold for liquid water to exist on its surface and thus making it
unlikely that life could develop. We know that water is the solvent of all life on
Earth, but what if we replaced water with a liquid hydrocarbon? Although water is a
stronger solvent, it's more chemically reactive and can break down large
organic molecules through hydrolysis. If life on Titan used liquid methane as a
solvent, then it would not face the risk of its biomolecules being destroyed
through hydrolysis. Life-forms living in Titan's rivers, lakes, or seas of liquid
hydrocarbons would intake hydrogen in place of oxygen. React it with acetylene
instead of glucose and produce methane instead of carbon dioxide. By comparison
some methanogens on Earth obtain energy by reacting hydrogen with carbon
dioxide producing methane and water. If methanogenic life existed in sufficient
numbers then a measurable effect of the hydrogen and Titan's atmosphere should
be observed. Curiously, scientists have found levels
of hydrogen and acetylene near the surface to be much lower than expected.
The physics of diffusion causes the higher concentration of hydrogen in
Titan's upper atmosphere to flow downward at a rate of 1,025 molecules per second,
but near the surface the downward flowing hydrogen apparently disappears.
Could this be the result of methanogenic life consuming hydrogen
on Titan's surface? While this discovery suggests a real potential for life on
Titan, some scientist caution that other explanations like human error or
meteorological processes are more likely. It's also possible that a mineral
catalyst is present that enables hydrogen and acetylene to react
chemically but we don't know of any such catalyst to date and the discovery of
one might be more surprising than if we actually did find life on Titan. Assuming
life did arise on Titan, how could it form a stable cell without liquid water?
On Earth, cells rely on a phospholipid bilayer, the protective structure that
separates the inside of the cell from the outside world. These fatty molecules
require water to exist. Scientists began looking for compounds that could allow
cellular life to thrive in Titan's methane lakes and seas. They found the
organic compound acrylonitrile could form a hollow microscopic sphere that
they dubbed an azotosome. This protective sheet would provide the
separation necessary for a stable cell membrane. As it turns out astronomers
have discovered a lot of this stuff in Titan's atmosphere while observing it
from the Alma Observatory in Chile. Carried to the surface by methane rain,
NASA Goddard's team estimate that Titan's sea Ligea Mare could have accumulated
enough acrylonitrile to form about 10 million azotosomes in every
milliliter or quarter teaspoon of liquid. That's compared to roughly a million
bacteria per milliliter of coastal ocean water on Earth. Further studies of Titan's atmospheric gases found something miraculous. When energy was applied to a
combination of the same gases found on Titan, some of the compounds produced
included the five nucleotide bases that constitute the building blocks of DNA
and RNA, as well as amino acids the building blocks of protein. Life as we
know it could not exist without these vital elements and it seems likely that
even exotic life forms would require something similar. All the evidence suggests an exciting
potential for life to arise and thrive in Titan's adverse environment, but we
just can't say for certain without sending another probe to study the
surface of Titan's methane lakes and seas, which is precisely what NASA is planning.
The most exciting idea involves a submersible autonomous vehicle. Launching
by the year 2038, this submarine would splashdown and Titans largest sea, the
Kraken Mare, becoming the first submarine to explore the depths of an
extraterrestrial sea. The addition of a submarine to NASA's fleet would expand
their capabilities to include situnautical operations. A Titan sub could prove incredibly
useful in the search for life within Titan's seas, but it might also offer clues
to how life on Earth formed. With an array of sophisticated autonomous instruments
onboard, the submarine would observe and analyze samples from the bottom of
Kraken Mare. It's almost eerie to think of what we could find while diving the
depths of a liquid methane sea. Several other mission ideas have been proposed
in the wake of Cassini's incredible discoveries that has left us with an
endless supply of intriguing questions. These include a balloon circumnavigating
Titan's atmosphere from an altitude of 10 kilometers, a robotic aircraft that
would photograph Titan's surface as it cruised through the atmosphere, and a
boat that has small propellers allowing it to explore the surface and shorelines
of Titan's seas, lakes, and rivers. These future endeavors are beyond exciting, but
we'll have to remain patient for the time being since
these are just preliminary proposals. We face crucial engineering challenges
ahead if we ever hope to boldly attempt a mission to study an extraterrestrial
sea with a submersible autonomous vehicle. For now, the question remains...
Will we find life upon our return to this orange moon? No matter what the
future holds, Titan will always remain one of the most extraordinary worlds in
our quiet corner of the galaxy. Thank you for watching to the end! Be sure
to subscribe to my channel for more documentaries in the future and let me
know what you thought in the comments below. Thank you also to my patrons whose
support helps to cover some of the expenses I invest in producing these
videos. Visit my patreon page if you'd like to help out too! Until next time my
friends, I'm Tex, happy orbiting.
I just learned a lot about Titan. thank you
1:09 “While it seems sentient life is exceedingly rare...” I turned it off.
We don’t know how rare sentience is. We just don’t. The assertion that we have any concept at all of the statistical likelihood of sentience or any other metric is a simple admission of our own intellectual shortcomings. “We don’t know what we don’t know.” -Donald Rumsfeld