Titan (satellite): characteristics, composition, orbit, movement

Titan is one of the satellites of the planet Saturn and the biggest of all. Its surface is icy, is larger than Mercury and has the densest atmosphere of any satellite 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 sighted the satellite with a telescope for the first time. Huygens did not call him Titan, but simply Luna Saturni , which in Latin is equivalent to saying “moon of Saturn”. 

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 Cronus, the father of 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 Hubble Space Telescope observations have greatly increased knowledge about this satellite, which in itself is a fascinating world. 

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

Furthermore, by having its axis of rotation tilted, Titan enjoys seasons, although the duration is different from that of Earth.

Because of that, as well as having its own atmosphere and its large size, Titan is sometimes described as a miniature planet and scientists focus on getting to know it better, to find out if it harbors or is capable of harboring life.

General features

Size

Titan is the second largest satellite, second only to Ganymede, the huge moon of Jupiter. In size, it is larger than Mercury, as the small planet is 4,879.4 km in diameter and Titan is 5,149.5 km.

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 its mass and volume. Titan’s mass can be determined by Kepler’s third law, as well as data provided by space missions.

Titan’s density turns out to be 1.9 g/cm 3 , much lower than that of rocky planets. It just means that Titan has a large percentage of ice – not just water, ice can be other substances – in its composition.

Atmosphere

The satellite has a dense atmosphere, which is rare in the solar system. This atmosphere contains methane, but the major component is nitrogen, as does the Earth’s atmosphere.

No water in it, nor carbon dioxide, but no other hydrocarbons are present because sunlight reacts with methane giving rise to other compounds such as acetylene and ethane.

no magnetic field

As for magnetism, Titan does not have its own magnetic field. Being on the edge of Saturn’s radiation belts, many highly energetic particles still hit Titan’s surface and fragment the molecules there.

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A hypothetical traveler arriving at Titan would find a surface temperature in the order of -179.5°C and a perhaps uncomfortable atmospheric pressure: one and a half times the value of the pressure of the land at sea level.

Rain

It rains on Titan because methane condenses in the atmosphere, although this rain often fails to reach the ground as it partly evaporates before then.

Summary of Titan’s main physical characteristics

Composition

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

Rocks contain iron and silicates, while ice creams are not all water, although there is a mixture of water and ammonia beneath the frozen layer of the crust. There is oxygen on Titan, but it is linked to groundwater.

Inside Titan, as on Earth and other bodies in the solar system, there are radioactive elements that produce heat as they break down 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 spacecraft, which managed to descend to the surface of the satellite, where it found samples of the evaporation of this compound. He also detected regions in which radio waves are poorly reflected, similar to the way they are reflected in terrestrial lakes and oceans.

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

The atmosphere on Titan

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 seen in the images.

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

It also has a layer of atmospheric pollution, which dulls the surface and in which there are suspended hydrocarbon particles. 

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

Atmospheric gases

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

Methane is a greenhouse gas whose presence prevents Titan’s temperature from falling further. However, the outermost layer, composed of widely dispersed gases, is reflective and neutralizes the greenhouse effect.

Hydrocarbons

Among the hydrocarbons observed on Titan, acrylonitrile is impressive , at concentrations of up to 2.8 parts per million (ppm), detected by spectroscopic techniques.

It is a compound widely used in the manufacture of plastics and which, 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 can reach the surface, condensing in the lower layers of the atmosphere and then precipitating with rain. 

In addition to acrylonitrile, on Titan there are tholins or tolins,  curious organic compounds that appear when ultraviolet light breaks down methane and separates nitrogen molecules. 

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

Such discoveries are very interesting, although the conditions on the satellite are not suitable for terrestrial life, mainly due to extreme temperatures.

How to watch 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 needed.

Even so, it is not possible to notice many details, because Titan does not shine as bright as the satellites of Galilee (the great satellites of Jupiter).

Also, Saturn’s large size and brightness can sometimes obscure the presence of the satellite, so it is necessary to look for the furthest moments between them to distinguish the satellite.

Orbit

Titan takes almost 16 days to rotate around Saturn and this rotation is synchronized with the planet, meaning it always shows the same face.

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

This is due to tidal forces, which not only elevate liquid masses, which is the most appreciated effect on Earth. They are also able to lift the crust and deform planets and satellites.

Tidal forces gradually decrease the satellite’s speed until the orbital speed equals that of rotation.

rotary movement

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

There are stations on Titan due to the inclination of the axis of rotation by 26º in relation to the ecliptic. But unlike Earth, each would last approximately 7.4 years.

In 2006, the Cassini spacecraft brought in images showing rain (methane) at Titan’s north pole, an event that would mark the beginning 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 certainly be drying up at the same time.

Internal structure

The following diagram shows Titan’s internal layered structure, built by bringing together the evidence gathered from Earth observations and that provided by the Voyager and Cassini missions:

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-Nucleus composed of water and silicates, although the possibility of a rocky inner core, based on silicates, is also addressed.

-Several layers of ice and liquid water with ammonia

-Icing on the outside.

The diagram also shows the dense atmospheric layer covering the surface, in which the above-mentioned layer of tholin-type organic compounds and finally a weaker outer layer of smoke stands out.

geology

The Cassini spacecraft, which landed on Titan in 2005, investigated the satellite using infrared and radar cameras 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 younger, around 100 million years ago, according to estimates. This is possible thanks to the great geological activity.

The images reveal icy hills and darker, more colorful surfaces.

There are few craters, as geological activity erases them soon after their formation. Some scientists have claimed that Titan’s surface is similar to the Arizona desert, although ice replaces the rocks.

Smoothly rounded ice edges were found at the site of the probe’s descent, as if fluid had molded them long ago.

There are also canal-filled hills that slope gently down to the plain and the methane lakes described above, as well as islands. These lakes are the first stable liquid bodies found at a location outside the Earth itself and are located near the poles.

Relief is generally not very pronounced on Titan. The highest mountains reach about a kilometer or two in height, according to altimetry data.

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

In fact, all of these phenomena occur on Earth, but in a very different way, as methane has replaced water on Titan and is also much further away from the Sun. 

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