TITAN (SATELLITE): CHARACTERISTICS, COMPOSITION, ORBIT, MOVEMENT - ARTE - 2025

Titan is one of the satellites of the planet Saturn and the largest of all. Its surface is icy, it is larger than Mercury, and it has the densest atmosphere of all the satellites in the solar system.

From Earth, Titan is visible with the help of binoculars or telescopes. It was Christian Huygens (1629-1695), a Dutch astronomer, who in 1655 spotted the satellite with a telescope for the first time. Huygens did not call it Titan, but simply Luna Saturni, which is Latin for "moon of Saturn."

Figure 1. Titan orbiting Saturn. Image of the are Cassini. Source: NASA.

The name Titan, derived from Greek mythology, was proposed by John Herschel (1792-1871), son of William Herschel, in the mid-19th century. The Titans were the brothers of Cronos, father of the time for the Greeks, equivalent to the Saturn of the Romans.

Both the space missions carried out during the last half of the 20th century and the observations of the Hubble Space Telescope greatly increased the knowledge about this satellite, which is in itself a fascinating world.

To begin with, on Titan there are meteorological phenomena similar to those on Earth, such as winds, evaporation and rain. But with a fundamental difference: on Titan, methane plays an important role in them, since this substance is part of the atmosphere and the surface.

In addition, because its axis of rotation is tilted, Titan enjoys seasons, although the duration is different from those of Earth.

For this and also because it has its own atmosphere and its large size, Titan is sometimes described as a miniature planet and scientists have focused on getting to know it better, to know if it harbors, or is capable of harboring life.

General characteristics

Size

Titan is the second largest satellite, second only to Ganymede, the huge moon of Jupiter. In size it is larger than Mercury, since the small planet is 4879.4 km in diameter and Titan is 5149.5 km in diameter.

Figure 2. Comparison of sizes between the Earth, the Moon and Titan, bottom left. Source: Wikimedia Commons. Apollo 17 Picture of the Whole Earth: NASA Telescopic Image of the Full Moon: Gregory H. Revera Image of Titan: NASA / JPL / Space Science Institute / Public domain

However, Titan has a large percentage of ice in its composition. Scientists know this through its density.

Density

To calculate the density of a body, it is necessary to know both its mass and its volume. Titan's mass can be determined through Kepler's third law, as well as data supplied by space missions.

Titan's density turns out to be 1.9 g / cm ³, well below that of rocky planets. This only means that Titan has a large percentage of ice - not just water, the ice can be other substances - in its composition.

Atmosphere

The satellite has a dense atmosphere, something rare in the solar system. This atmosphere contains methane, but the major component is nitrogen, just like the Earth's atmosphere.

It does not have water in it, nor does it have carbon dioxide, but there are other hydrocarbons present, because sunlight reacts with methane, giving rise to other compounds such as acetylene and ethane.

No magnetic field

As for magnetism, Titan lacks its own magnetic field. Because it is at the edge of Saturn's radiation belts, many highly energetic particles still reach the surface of Titan and break up molecules there.

A hypothetical traveler arriving on Titan would find a surface temperature of the order of -179.5 ºC and an atmospheric pressure that was perhaps uncomfortable: one and a half times the value of the earth's pressure at sea level.

Rain

On Titan it rains, because methane condenses in the atmosphere, although this rain may often not reach the ground, as it partly evaporates before it reaches the ground.

Summary of the main physical characteristics of Titan

Composition

Planetary scientists infer from Titan's density, which is roughly twice that of water, that the satellite is half rock and half ice.

The rocks contain iron and silicates, while the ice is not all water, although under the frozen layer of the crust there is a mixture of water and ammonia. There is oxygen on Titan, but tied to water in the subsurface.

Inside Titan, just like on Earth and other bodies in the solar system, there are radioactive elements that produce heat as they decay into other elements.

It is important to note that the temperature on Titan is close to the triple point of methane, which indicates that this compound can exist as a solid, liquid or gas, playing the same role as water on Earth.

This was confirmed by the Cassini probe, which managed to descend on the surface of the satellite, where it found samples of the evaporation of this compound. It also detected regions in which radio waves are weakly reflected, analogously to how they are reflected in lakes and oceans on Earth.

These dark areas in the radio images suggest the presence of bodies of liquid methane, between 3 and 70 km wide, although more evidence is needed to definitively support the fact.

The atmosphere on Titan

The Dutch astronomer Gerard Kuiper (1905-1973) confirmed in 1944 that Titan has its own atmosphere, thanks to which the satellite has the characteristic orange-brown color that can be seen in the images.

Later, thanks to data sent by the Voyager mission in the early 1980s, it was found that this atmosphere is quite dense, although it receives less solar radiation due to distance.

It also has a layer of smog, which dulls the surface and in which there are hydrocarbon particles in suspension.

In the upper atmosphere of Titan winds of up to 400 km / h develop, although approaching the surface the panorama is a little more serene.

Atmospheric gases

Regarding its composition, atmospheric gases consist of 94% nitrogen and 1.6% methane. The rest of the components are hydrocarbons. This is the most characteristic feature, because apart from the Earth's atmosphere, no other in the solar system contains nitrogen in such quantity.

Methane is a greenhouse gas whose presence prevents Titan's temperature from dropping further. However, the outermost layer, made up of widely dispersed gases, is reflective and counteracts the greenhouse effect.

Hydrocarbons

Among the hydrocarbons observed on Titan, acrylonitrile is striking, in a concentration of up to 2.8 parts per million (ppm), detected through spectroscopic techniques.

It is a compound widely used in the manufacture of plastics and, according to scientists, is capable of creating structures similar to cell membranes.

Although acrylonitrile was initially detected in the upper layers of Titan's atmosphere, it is believed that it may well reach the surface, condensing in the lower atmospheric layers and then falling in the rain.

Besides acrylonitrile, on Titan there are tholins or tholins, curious compounds of an organic nature that appear when ultraviolet light fragments methane and separates nitrogen molecules.

The result is these more complex compounds that are believed to have existed on early Earth. They have been detected on icy worlds beyond the asteroid belt and researchers are able to produce them in the laboratory.

Such findings are very interesting, although the conditions of the satellite are not suitable for terrestrial life, especially because of the extreme temperatures.

How to observe Titan

Titan is visible from Earth as a small point of light around the giant Saturn, but the help of instruments such as binoculars or telescopes is necessary.

Even so, it is not possible to notice a lot of detail, because Titan does not shine as much as the Galilean satellites (the great satellites of Jupiter).

In addition, the large size and brightness of Saturn can sometimes hide the presence of the satellite, which is why it is necessary to look for the moments of greatest distance between the two to distinguish the satellite.

Orbit

Titan takes almost 16 days to rotate around Saturn and such rotation is synchronous with the planet, which means that it always shows the same face.

This phenomenon is very common among satellites in the solar system. Our Moon, for example, is also in synchronous rotation with the Earth.

Figure 3. Titan's orbit highlighted in red, along with that of Saturn's main satellites: Hyperion and Iapetus are the outermost to Titan, while the innermost are, in order: Rhea, Dione, Tethys, Enceladus and Mimas. Source: Wikimedia Commons. ! Original: Rubble pileVector: Mysid. / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)

This is due to the tidal forces, which not only lift the liquid masses, which is the effect that is most appreciated on Earth. They are also capable of lifting the crust and warping planets and satellites.

The tidal forces gradually slow down the speed of the satellite until the orbital speed equals the rotational speed.

Rotatory motion

Titan's synchronous rotation means that its period of rotation around its axis is the same as the orbital period, that is, approximately 16 days.

There are stations on Titan because of the tilt of the axis of rotation at 26º from the ecliptic. But unlike Earth, each would last for about 7.4 years.

In 2006, the Cassini probe brought up images showing rain (from methane) on Titan's north pole, an event that would mark the start of summer in the satellite's northern hemisphere, where methane lakes are believed to exist.

The rains would make the lakes grow, while those in the southern hemisphere would surely be drying up around the same time.

Internal structure

The diagram below shows Titan's layered internal structure, built by pooling evidence collected from Earth observations plus that from the Voyager and Cassini missions:

-Nucle composed of water and silicates, although the possibility of a more internal rocky core, based on silicates, is also handled.

-Various layers of ice and liquid water with ammonia

-Outermost crust of ice.

Figure 4. Internal structure of Titan, according to theoretical models. Source: Wikimedia Commons. Kelvinsong / CC BY (https://creativecommons.org/licenses/by/3.0).

The diagram also shows the dense atmospheric layer that covers the surface, in which the layer of organic compounds of the tholin type mentioned above stands out, and finally a more external and tenuous layer of smog.

geology

The Cassini probe, which landed on Titan in 2005, investigated the satellite using infrared cameras and radar, capable of penetrating the dense atmosphere. The images show a varied geology.

Although Titan was formed along with the rest of the members of the solar system just over 4.5 billion years ago, its surface is much more recent, around 100 million years according to estimates. That is possible thanks to great geological activity.

Images reveal icy hills and smooth surfaces of darker color.

There are few craters, since geological activity erases them shortly after they form. Some scientists stated that Titan's surface is similar to the Arizona desert, although ice takes the place of rock.

Gently rounded ridges of ice were found at the site of the probe's descent, as if a fluid had shaped them long ago.

There are also hills lined with channels gently sloping down to the plain and the methane lakes described above, as well as islands. These lakes are the first stable liquid bodies found in a place outside the Earth itself and are located near the poles.

Figure 5. Image of Titan taken by the Huygens probe at 10 km altitude. Source: ESA / NASA / JPL / University of Arizona / Public domain.

The relief in general is not very marked on Titan. The highest mountains reach about one or two kilometers high, according to altimetric data.

In addition to these features, on Titan there are dunes caused by the tides, which in turn generate strong winds on the surface of the satellite.

In fact, all these phenomena occur on Earth, but in a very different way, since on Titan methane took the place of water, and it is also much further from the Sun.

References

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