A look at Titan, Saturn's largest moon

Saturn's largest moon

Italian astronomer Giovanni Cassini and Dutch astronomer Christiaan Huygens both made detailed observations of Saturn and its moons.

Huygens discovered Titan, Saturn's largest moon. Actually, calling these men astronomers is selling them short. They were scientists in a more general sense, making contributions in many different fields. Back in the 17th century, when they lived, doing cutting edge science did not involve the degree of specialization that is required today.

When a space mission was planned to make closer observations of Saturn and its moons, it was logical to name the mission after these men. The mission involved two spacecraft. One, named Cassini, would orbit around the Saturn system making detailed observations of the planet, its rings and its moons. The other, named Huygens, would make a soft landing on Titan. The pair were launched on Oc. 15, 1997 and entered orbit around Saturn on July 1, 2004.

The trip took that long because the launcher was not powerful enough to give the spacecraft a direct trip to Saturn, it had to do flybys of Venus, Earth and Jupiter to gain the speed needed to reach Saturn.

On reaching the Saturn system, the Huygens spacecraft separated and headed for Titan. After surviving the heat of atmospheric entry, where it used the drag of the atmosphere to slow from many kilometres a second down to a few hundred kilometres an hour, it deployed a parachute, and descended slowly to manage a gentle landing on Titan's surface. There is a fascinating NASA video of the view from Cassini as it descended. https://science.nasa.gov/resource/a-view-from-huygens/

More information about the Huygens mission and more images are available here. https://science.nasa.gov/mission/cassini-huygens/

There are reasons for our particular interest in Titan, compared with the other moons in the Solar System. As soon as telescopes improved enough, astronomers noticed that whereas the other moons in the Solar System are largely colourless or very subtly coloured, like our moon, Titan is orange-brown. Whereas the other moons have either no atmosphere, or maybe a very thin one, Titan has a very thick atmosphere, thicker than the Earth's.

Around 9.6 times further from the Sun than the Earth, Titan receives only about 1% of the solar heat and light. This makes Titan a really cold place, with a surface temperature of about -180 C. At that temperature water would be a permanently frozen rock mineral. However, under Titanian conditions, methane can be present as a gas or a liquid, playing the same role as water on Earth, forming lakes and rivers. Huygens landed on a dry streambed.

The brown atmosphere is due to hydrocarbons and other organic (carbon-based) molecules. A witches brew of chemicals have been detected so far, probably formed in the upper atmosphere, in chemical reactions driven by sunlight.

Here on Earth, the foundation of life was organic molecules dissolved and interacting in seawater. Could organic molecules dissolved in liquid methane provided a foundation for life on Titan?

There is little or no oxygen in Titan's atmosphere, but when life first started on Earth there was no oxygen here either. One important difference is water is a solvent in which chemicals can easily break up and then combine to make new ones. Liquid methane is less effective for this. However, that does not rule out the possibility of life. If it exists it will be very different from life here. We need to have a closer look at that world.


• Venus lies low in the dawn glow.

• Jupiter shines high in the south after sunset.

• The Moon will reach first quarter Feb. 16.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.

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About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]

The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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