Moons of the Solar System ② - Titan, the Foggy World of Organics

A series on the moons of the solar system.
Last time, I wrote about the largest moon, Ganymede.

The icy giant was a quiet world, yet one that held the potential for life.

Now, this time, we look at Saturn's moon, Titan, which is shrouded in organic fog. It is the second-largest moon in the solar system, following Ganymede. Let's get started!

Overview: A moon with a dense atmosphere

Titan, the sixth moon of Saturn.
Its defining feature is that it is the only moon in the solar system with a dense atmosphere.

It has a diameter of approximately 5,150 km. It is the largest of Saturn's moons.
Like Ganymede, it is even larger than the planet Mercury.

Its orbital period is about 15.95 days.
Titan is also tidally locked to Saturn, meaning it always keeps the same face pointed toward the planet.

Atmosphere and internal structure

Titan's atmosphere is composed mainly of nitrogen, with ethane and methane mixed in.
This atmosphere is very thick, and the surface pressure is actually 1.5 times that of Earth.
Furthermore, methane is broken down by sunlight into complex hydrocarbons, which then lead to organic molecules. The fog created by this process is what dyes Titan's sky orange.

Additionally, Titan's atmosphere experiences 'super-rotation,' where it rotates faster than the body itself.
This phenomenon has only been clearly observed on Venus and Titan.
Winds in the upper atmosphere blow at tens of meters per second, exceeding the speed of its rotation.

The surface temperature is a frigid -179.2°C.
Methane and ethane turn into liquid, fall to the surface as rain, and then become rivers that carve the landscape and flow into lakes.

Even if it is not water, it is very similar to Earth in that it has a 'climate cycle involving liquids.'
Titan is the only place in the solar system other than Earth where stable liquids have been confirmed on the surface.

Titan's interior is thought to consist of a 'subsurface ocean' made of liquid water containing salt and ammonia beneath an icy crust, with another layer of ice below that, and a rocky core made of silicate rock at the center.
Like Ganymede, it is believed that this subsurface ocean may contain more water than Earth's oceans.
However, this ocean is rich in organic matter and ammonia, which is a feature that distinguishes it from Ganymede.

*The illustration is a model image based on observation data from the Cassini spacecraft.

Possibility of life

Because Titan is rich in complex organic compounds, there has long been hope that life might exist there.
Researchers are focusing on two possibilities.

One is 'water-based life' in the subsurface ocean, similar to Ganymede. In Earth's deep oceans, there are organisms that live using the chemical reactions of hydrothermal vents as energy, without relying on sunlight.
A similar environment might exist in Titan's subsurface ocean, within the extremely cold water containing ammonia and salt.

The other is a possibility unique to Titan: life that is completely different from Earth's, using the hydrocarbons and organic matter in the atmosphere as an energy source.
If such life were discovered, we would be witnessing a new common knowledge of the universe: that 'life can emerge even without water.'

History of Exploration

The history of Titan exploration began with Pioneer 11 in 1979, followed by Voyager 1 in 1980 and Voyager 2 in 1981.
However, those observations were hindered by Titan's thick atmosphere, leaving a lack of detailed information.

Titan, which had been shrouded in mystery, had its details revealed by the Cassini and Huygens probes.
Cassini arrived at Saturn in 2004 and subsequently conducted explorations of Titan. It performed several close flybys and photographed Titan from above.

Cassini also deployed the Huygens probe in 2005. Released into the upper atmosphere of Titan, Huygens descended using a parachute and landed on the surface.

The surface of Titan observed by Huygens showed round pebbles and traces of riverbeds.

And now, NASA is moving forward with the 'Dragonfly' mission to explore Titan.
It is scheduled to launch in 2028 and arrive at Titan in 2034.
While it's just a blink of an eye in cosmic time, it's quite a bit into the future for us.

Dragonfly is a probe with rotors like a drone. It is the perfect exploration method for Titan, which has a dense atmosphere.
Unlike previous probes that remained at a single location, it can fly around and investigate many different places.

So cool...!
Dragonfly's main objective is to investigate chemical reactions before the birth of life (prebiotic chemistry).

Observation Methods

Although Titan is large in diameter, as a moon of Saturn, it cannot be observed with binoculars from Earth.
It seems it can be seen as a small dot with a commercially available astronomical telescope.
To capture its characteristic orange color, large telescopes like the Subaru Telescope or the Hubble Space Telescope are required.

Summary

Titan, the second-largest moon in the solar system.
This world was somewhat similar to Earth, not only in its size but also in its dense atmosphere, liquid circulation, and even the potential for life.
It is a moon full of personality, different from Ganymede.

Next time, I plan to summarize 'Callisto,' the third-largest moon in the solar system.

Thank you for reading until the end.
If the article left even a small impression on you, I would be happy if you could let me know by clicking the [Like] button.
See you next time!

Sources and References

• Wikipedia - Titan (moon) : Link

• NASA / JPL / Space Science Institute, PIA06122: Titan’s Colorized UV View, link

• NASA / JPL-Caltech, Layers of Titan (annotated), link

• NASA / JPL, PIA07232: First Color View of Titan’s Surface, link

• NASA / JHU-APL, Dragonfly rotorcraft-lander concept, link

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