Titan – The “Earth-like” moon

Nuvin Wickramasinghe

Titan is Saturn’s largest moon, the second largest natural satellite in the solar system, behind Jupiter’s Ganymede. Originally discovered in 1655, Titan has been revealed to be one of our solar system’s most bizarre satellites over time, especially regarding its atmosphere, surface and structure sharing similarities with Earth.

Rivers, lakes, sand dunes, canyons, a weather cycle, an atmosphere etc. are all found on Titan. Despite these features being composed of different materials to our planet, they all are Earth-like features found on this mysterious moon (Waldek, 2022).

Titan appeared in the popular film “Star trek” (2009), where the U.S.S Enterprise comes out of warp in the large moon’s atmosphere to ambush enemy ships attacking Earth. It also appears in TV shows such as “Futurama” and “Eureka” and in the famous anime “Cowboy Bebop” (NASA, 2022a). Iconic supervillain Thanos was also born on Titan in the original marvel comics (albeit the moon appears vastly different) (Aaron & Bianchi, 2013). In the movies, he’s from a faraway, fictional planet in a different solar system called Titan.

Timeline of major discoveries on Titan

On March 25th 1655, astronomer Christiaan Huygens discovered the bizarre moon. Then, Gerard Kuiper in 1944 discovered that the moon had a thick atmosphere, something extraordinary. He did this by finding methane when passing reflected sunlight from Titan through a Spectrometer (Kuiper, 1944). Pioneer 11 (1979) confirmed astronomers’ predictions regarding temperature and mass. Following this, Voyager 1 (1980) pictured the somewhat orange body we know Titan to be today. It also revealed its atmosphere to be primarily nitrogen (like Earth), whilst also containing other hydrocarbons (NASA, 2022b).

The Cassini-Huygens mission was a joint NASA/ESA (European Space agency) effort. From 2004 to 2017, NASA’s Cassini spacecraft orbited Saturn to collect data of the planet and its moons. On 14 January 2005, the ESA’s Huygens space probe reached Titan where the world obtained its first pictures from Titan, as well as furthering our understanding of the large moon. The entire operation was a huge success with the probe being the largest interplanetary spacecraft ever built and Huygens being the farthest landing from Earth ever made (ESA, n.d. a).

Building on the Cassini-Huygens success, NASA plan to launch the Dragonfly spacecraft in 2027 following the discoveries of water and the Earth-like atmosphere on Titan. Scientists hope that this mission will be able to help study the possible start of life due to Titan sharing many features of a young Earth. Dragonfly will sample and examine the structures and chemicals there to hopefully gain invaluable information about life as we know it, and as we don’t (The planetary society, n.d.).

Size, orbit and formation

Some information about Titan: The large moon has a radius of about 2575km (nearly 50% wider than the Earth’s moon), as well as having a mass 1.8 times larger than Earth’s moon. Titan takes 15 days and 22 hours to complete 1 full orbit of Saturn (NASA, 2022c). As for how Titan came into existence is quite unique. Some moons, such as Neptune’s Triton was formed elsewhere in the solar system then pulled into orbit by the planet’s gravitational pull. Alternatively, some moons are created as residue from impacts such as the widely believed theory that the Earth’s moon was formed from an impact of the Earth with a smaller object called Theia. Other moons are believed to have been born in circumplanetary discs. These discs exist around a planet when an infant star is making a planetary system. Generally, large moons formed in the dusty material in the discs spiral towards the planet due to the drag from the surrounding gas and dust. However, Yuri Fujii and Masahiro Ogihara, at the Department of Physics, Nagoya University, and National Astronomical Observatory of Japan, created a model that used updated information about circumplanetary discs. The models hinted at a “safety zone” for larger moons where high pressure gas coupled with being a significant distance away from the planet lead to the moon being pushed outwards, causing a balance of forces, preventing Titan from being pulled into Saturn. Once these discs cease to exist, any movement towards or away by Titan from Saturn stops. Titan being formed during the creation of the solar system is supported by data collected by the Huygens’s probe on Titan’s nitrogen isotope ratio. It resembles material found in the Oort cloud, a collection of icy objects that was formed around the same time as the solar system, which implies Titan existed and was created during the formation of the planetary system (Dartnell, 2020; Leman, 2020).

Atmosphere, surface and structure

Titan’s atmosphere is what makes it such a scientific hotspot for discovery. The fact that it’s a moon with an atmosphere immediately draws much intrigue towards it. Unlike Earth’s atmosphere, Titan’s looks like a thick layer around it. This is because the moon is a lot smaller than earth but its atmosphere is 1.9 times larger than earth’s, and its weaker gravity means it pulls its atmosphere down less strongly. Voyager 1 found that Titan’s atmosphere consists of: Nitrogen (around 95 percent), methane and hydrogen (about 5 percent) and hydrocarbons (from broken up methane due to the sun’s UV light) that many believe give Titan its orange colour. However, due to this continuous breaking down of methane, the moon should’ve ran out of it by now, meaning there must be a source that replenishes the methane, which researchers suspect to be cryovolcanoes (Volcanoes that erupt liquids and vapours into an environment that is below their freezing point, similar to magma from Earth’s volcanoes). Despite this, it still is yet to be confirmed on whether this refreshes methane although its presence would also validate that Titan is alive and still changing from its interior. (Astrum, 2019)

Titan’s special surface and structure also contributes to its uniqueness. Cassini discovered something remarkable, a layer of liquid water beneath the moon’s surface. Saturn’s strong gravity alters Titan’s shape as the moon orbits it, similar to the tides on Earth. If Titan consisted of only rock, the crust will rise and fall by about 1 meter. In spite of this, Titan experiences tides of about 10 meters, meaning Titan isn’t solely made of rock. A liquid layer beneath the outer crust would allow Titan to expand and compress to this magnitude. Due to the surface of Titan being water ice, it’s most likely that Titan’s subsurface ocean is mainly liquid water. The presence of an ocean gives scientists further hope for life on Titan although nothing can be confirmed yet. Experts believe that life is likely to exist when liquid water meets rock, but the current observations can’t tell what the ocean floor of Titan is made of (NASA, 2012a).

Another success of Cassini-Huygens is that the probe developed our comprehension of Titan’s climate. In the lower layers of the atmosphere, it possesses a fully functioning seasonal weather cycle, almost identical to the Earth’s hydrological cycle, except with methane. Titan’s freezing surface temperatures (approximately -180 degrees Celsius) permits methane to form clouds and rain, which then fall onto the surface, filling the lakes and rivers. However, as mentioned prior it’s still yet to be confirmed how methane clouds continue to exist due to photochemical reactions (reactions that occur due to the absorption of energy from light) involving the sun’s light that breaks down methane, with the theorized cryovolcanoes being the possibility many researchers suspect (Mitchell, 2016).

Cassini-Huygens also found its surface to have rivers and lakes of hydrocarbons. During Huygens’s descent, features that resembles rivers from Earth were seen except the involved fluid was methane. The probe then landed on a frozen surface with the below picture being taken. Cassini also revealed a surface littered with these hydrocarbon lakes, the first time this had ever been seen outside of Earth. For example, Ligeia Mare and the Kraken Mare are two lakes found on Titan, both of which are larger in surface area than Lake Superior in North America (ESA, n.d. b;

Astrum, 2019). Life

First I’ll look at the possibility of humans staying on Titan. Due to the density of the air, we could theoretically walk around Titan without a spacesuit. Despite this, the freezing temperatures and the lack of oxygen means it isn’t feasible and likely unachievable for humans to stay on Titan (NASA, 2022c; NASA, 2022a).

However due to Huygens’s findings of an underground ocean of water arises the possibility of life within them, even though they will likely operate differently to life on Earth. There could even be life we are incapable of comprehending at this point in time present on Titan within these oceans of water or even in the lakes of hydrocarbons. There is still the possibility that Titan is lifeless or yet to develop life (NASA, 2022c).

As I see it, I am hopeful of some sort of discovery of life on Titan eventually. Something that can help us develop our understandings of the beginning of life on a celestial object. There are so many unique features to this moon (atmosphere, water etc.) that lead me to being optimistic for significant discoveries regarding Titan in the future.

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