This image of Ligeia Mare, one of the ethane and/or methane "seas" on Titan, was created with radar data from the Cassini spacecraft. The image has been artificially colorized; liquid ethane/methane is shown in blue, areas of "dry land" are brown. This sea is near Titan's North Pole, and is slightly larger (in area) than Lake Superior on Earth.
Click on image for full size
Image courtesy of NASA/JPL/USGS.

The Poles of Titan

Titan is Saturn's largest moon, and the second largest moon in our Solar System. It is the only moon with a thick atmosphere. Titan's poles are interesting places. Scientists have discovered lakes at both poles, and even small seas near the North Pole. They have also spotted clouds, some of which are huge, at each of the moon's poles.

Astronomers have long hypothesized that there might be lakes or even oceans of liquid methane and/or ethane on Titan. Images from the Hubble Space Telescope in the 1990s and data from the Cassini spacecraft starting in 2004 confirmed these suspicions. So far, however, these lakes and seas have only been seen near Titan's poles. There are many lakes of various sizes, and even a couple of seas, near the North Pole. The region around the South Pole does not have any seas; and though fewer in number than in the North, it does have several lakes.

Titan is very cold; the surface temperature is around -179° C (-290° F). At those temperatures water ice is as hard as rock, and methane (natural gas, like the stuff that fuels many home furnaces) and ethane turn from gases into liquids. Titan's lakes and seas may contain ethane, methane, or both. They are the first stable bodies of surface liquid found beyond Earth.

The area around the North Pole is dotted with hundreds of small lakes. It also has some very large ones which astronomers are now calling seas. One (named Ligeia Mare) is about the size of North America's Lake Superior, the largest of the five Great Lakes. Another (dubbed Kraken Mare) may be even larger, about as big as the Caspian Sea - though it hasn't yet been completely mapped. One lake appears to be fed by a river that is over 200 km (124 miles) long and up to a kilometer (0.6 miles) wide. Ontario Lacus, similar in size and shape to Lake Ontario (the smallest of the Great Lakes) on Earth, is one of the larger lakes near Titan's South Pole. So far, only a handful of lakes have been spotted in the vicinity of the South Pole. A sea on Titan is called a "mare" (plural "maria"), while a lake is called a lacus (plural "laci").

So where did the liquid ethane and/or methane in the lakes and seas come from? Astronomers have spotted clouds over both of Titan's poles. Some scientists hypothesize that methane and/or ethane rain or snow may fall from those clouds to Titan's surface, filling the lakes. One idea claims that methane/ethane evaporates at the warmer summertime pole (the South Pole at the time of the early Cassini observations), is transported by the atmosphere to the other pole, and then falls as rain or snow at the winter pole - filling the lakes. This hypothesis would explain why lakes are more abundant near the North (the wintertime pole as of this writing in 2008) Pole and scarcer near the South (summertime) Pole. One of the clouds seen over the North Pole in 2007 was gigantic, covering an area half the size of the United States!

Last modified January 20, 2009 by Randy Russell.

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Hubble Space Telescope

The Hubble Space Telescope (HST) was one of the most important exploration tools of the past two decades, and will continue to serve as a great resource well into the new millennium. The HST is credited...more

Cassini

The Cassini probe began its journey to Saturn on October 15, 1997. It flew by Earth in August, 1999, before heading towards the distant planet. Cassini passed Jupiter in 2000 and then burned towards its...more

Methane - CH4

Methane is gas that is found in small quantities in Earth's atmosphere. Methane is the simplest hydrocarbon, consisting of one carbon atom and four hydrogen atoms. Methane is a powerful greenhouse gas....more

Changes of State: Solids, Liquids, and Gases

Any substance, called matter, can exist as a solid material, liquid, or gas. These three different forms are called states. Matter can change its state when heated. As a solid, matter has a fixed volume...more

The Poles of Saturn and Its Moons

There's a lot of strange and interesting stuff going on at both the North and South Poles of Saturn. Features at the poles of two of Saturn's moons, Titan and Enceladus, have also grabbed the attention...more

How Titan Formed

In many respects Titan is similar to the other icy moons, but Titan is the only icy moon to have an atmosphere that can be compared to other planets'. It is natural to ask how is this possible since Titan...more

The Environment of Titan, can there be Life?

Titan's atmosphere is a lot like the Earth's, except that it is very cold, from -330 degrees to -290 degrees! Like the Earth, there is a lot of Nitrogen and other complex molecules. There also may be an...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA