Titan's thick atmosphere, which appears orange, hides the moon's surface from view. A high-altitude haze layer appears as a faint ring around Titan. This image was captured by Cassini on October 24, 2004 at a distance of about one million km (621,371 miles).
Click on image for full size
Image courtesy NASA/JPL/Space Science Institute.
Titan is the largest moon of Saturn,
and the second largest moon in the entire
Solar System (Jupiter's moon Ganymede is
the largest). Titan's diameter is 5,150 km (3,200 miles), which is comparable
to the distance across the United
States. It is considerably larger than Earth's
moon, and is even larger than
two planets - Mercury and Pluto.
Titan orbits Saturn at a distance of 1,221,830 km (759,208
Titan has a dense atmosphere,
which, like Earth's atmosphere, is composed mostly of nitrogen. It is the only
moon in the Solar System possessing a substantial atmosphere. Atmospheric pressure at the surface of Titan is about 60% greater than the pressure at sea level
on Earth! Titan's atmosphere also contains a fair amount of methane, as well
as smaller quantities of various hydrocarbons created via the exposure of methane
to solar ultraviolet radiation. A smog-like haze in Titan's atmosphere prevents
us from directly observing
the moon's surface in visible wavelengths from Earth or orbiting spacecraft.
Titan's surface is
quite cold, with temperatures hovering around -178º C (-288º F). The European
Space Agency's Huygens
probe, which landed on the icy
moon in January 2005, has given us our first good look at the surface of
Titan. NASA's Cassini spacecraft is also
revealing details of the moon's surface via radar. Titan's surface has
areas, near its poles, dotted with numerous lakes of liquid methane and ethane!
Titan was discovered by the Dutch astronomer Christiaan
Huygens in 1655. Modern scientists are especially interested in Titan because
of its unusual history
and complex atmospheric chemistry. Some scientists think conditions on Titan
may be similar to those on Earth shortly before life
arose on our planet, making Titan a modern laboratory for studying the primordial
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