Who is Cassini-Huygens

Launched in October 1997, the Cassini-Huygens mission to Saturn and Titan was a joint effort of by ESA, NASA and the Italian space agency, Agenzia Spaziale Italiana (ASI). Cassini-Huygens reached Saturn on July 1, 2004. Months later, on December 25, 2004, the Huygens probe was released to land on Saturn's moon Titan on January 14, 2005.

ESA describes the mission objectives as the following:

1. what is the source of heat inside Saturn that produces 87 per cent more energy than the planet absorbs from sunlight?
2. what is the origin of Saturn's rings?
3. where do the subtle colours in the rings come from?
4. are there any more moons?
5. why has the moon Enceladus such an abnormally smooth surface? (Has recent melting erased craters?)
6. what is the origin of the dark organic material covering one side of the moon Iapetus?
7. which chemical reactions are occurring in Titan's atmosphere?
8. what is the source of methane, a compound associated to biological activity on Earth, which is so abundant in Titan's atmosphere?
9. are there any oceans on Titan?
10. do more complex organic compounds and 'pre-biotic' molecules exist on Titan?

As shown in the image above, Cassini's trajectory included several gravitational slingshot maneuvers: two Venus, one Earth and one Jupiter flybys to increase Cassini's momentum.

Most of what we know about Saturn is a result of the Voyager I and II and Cassini-Huygens probes. The Cassini probe is still in orbit around Saturn.

Ancient astronomers believe Saturn is a star in the evening sky.

1609 AD Galileo builds the first telescope. Gazing at Saturn, he discovers it's a planet with, what he believes, are two large moons.

1655 Dutch scientist Christiaan Huygens improves upon Galileo's telescope design and aims his better-quality telescope at Saturn: discovering that Saturn's two "moons" are actually a flat, thin ring encircling the planet. Huygens also discovers Saturn's largest moon, Titan.

1675 Jean-Dominique Cassini discovers that Saturn's 'ring' has an outer and an inner ring, separated by a dark band, which has become known as the "Cassini Division.'

1875ish Scottish physicist James Clerk Maxwell proves that Saturn's rings consist of many small particles, orbiting the planet like individual moons.

1944 The Dutch-born astronomer Gerard Kuiper discovers that Titan's unique atmosphere contains methane. Only Jupiter's moon Io and Neptune's moon Triton are known to have atmospheres, but they are very thin.

1979 Saturn is visited for the first time by Pioneer 11, which flies within 20,000 kilometers of the planet's top cloud layer. Pioneer 11 discovers that the 'Cassini' division isn't empty, as believed, but consists of thin dust rings. Furthermore, the probe discovers yet another ring beyond the outermost known ring and that Saturn has a strong magnetic field, more powerful than Earth's. The magnetic field means Saturn's core of liquid hydrogen and helium must be compressed so much that they exhibit the properties of a metal. Pioneer 11 also discovers that Saturn radiates more heat than it receives from the Sun.

1980 Voyager 1 visits Saturn, sending back the first high-resolution images of the planet, rings and satellites. Voyager 1 sees Saturnian cloud cover, storms, weather systems, and, for the first time, polar auroral lights. Surface features of some of the moons are also seen for the first time. Titan's atmosphere, however, proves impenetrable and Voyager 1 is unable to observe the moon's surface.

1981 Voyager 2 continues the study of Saturn, providing more close-up photos of the planet's rings and moons, discovering several new satellites. The probe also examines Saturn's upper atmosphere with its radar, before continuing its journey toward Uranus.

2004 The Cassini-Huygens spacecraft enters into orbit around Saturn. In June, it conducts a flyby of the moon Phoebe and two flybys of Titan, before releasing the Huygens probe on December 25, 2004. Huygens lands on the surface of Titan on January 14, 2005.

Saturn's auroras are glowing regions of ionized gas appearing at the poles, produced by charged particles from the solar wind.

Saturn's atmosphere is similar to Jupiter's. This color enhanced image [above] allows scientists to study the bands that run parallel to the equator, indicating violent winds. Saturn is one of the windiest places in the Solar System, with wind speeds of 1800 kilometers per hour at the equator. The temperature in the part of the atmosphere where "weather" occurs, the troposphere, ranges from about -130ºC to about +80ºC. The top visible cloud deck is made up of ammonia clouds, found about 100 kilometers below the top of the troposphere. The temperature there is about -250ºC. The hydrogen gas, which makes up most of Saturn's atmosphere, changes to liquid with depth as the pressure increases. Below the liquid hydrogen lies the heavier liquid helium. Scientists believe Saturn has a rocky core about ten times the mass of the Earth at the center.

Titan's atmosphere is mostly nitrogen with some organic compounds, such as methane. On earth the presence of methane is an indicator of life. So scientists are puzzled by the methane on Titan...where does it come from? Prior to Cassini, the Keck Observatory revealed methane-containing clouds near Titan's south pole. Did this mean Titan has weather similar to Earth's? Is Titan's surface solid or liquid? Little was known until the Cassini mission.

The Huygens probe discovered liquid methane on Titan's surface, punctuated by rocks of dirty ice. The liquid methane or ethane may form huge seas hundreds of miles across. Titan's high northern latitudes are dotted with these seas and lakes. There are also massive windblown sand dunes of dark brown organic material, which may accumulate and grow from smog particulates falling from the sky.

Although nitrogen is the dominant gas in Titan's upper atmosphere, methane is more abundant in the lower atmosphere. This primitive methane atmosphere is comparable to early Earth's.

Over the last several years, Cassini's radar observations of Titan have revealed what may be an internal ocean, underneath Titan's crust, similar to Jupiter's moon Europa. Scientists believe the ocean may be composed of water with a little ammonia.

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