The Cassini-Huygens Mission

The Cassini mission is a mission launched to Saturn on Oct 15 1997, and entered orbit in the Saturn system on June 30 2004. Its purpose is to study the planet, moons, and rings of the Saturn system.

Out of Respect for Copyrights - I've posted links to pictures instead of the linked images themselves.

The Cassini Probe

Its launch generated a lot of hype back in the 1990's. It carried a small nuclear battery, called a radio-isotope thermoelectric generator or RTG, which provided power and heat to the probe. Deep space probes operating far from the sun cannot get solar energy to run their instruments, and conventional batteries don't last years at a time, so RTGs are usually employed. This RTG caught the attention of the enviro-mental community, which latched onto the fact that it used a nuclear material (2kg of plutonium) to generate heat to run the device. The screaming protest was spectacular. They were prophesizing that if it were to crash over the gulf of Mexico, hundreds of thousands of people could die from nuclear contamination, and it would wipe out sea life in the area (2 kg of plutonium!).
Info about RTGs.
Of course, such concerns were absurd, first of all because of the extremely low amount of the nuclear fuel (think about it: if plutonium is that dangerous, why do we insist on weaponizing it and building atomic bombs at all? Why not just spray parts-per-billion powder over a country?), and second of all, because it is designed to break up in the upper atmosphere to disperse harmlessly. It's also an alpha emitter.

In any case, despite the hoopla, and protestors in Darth Vader masks, the mission launched successfully, did a swing-by of Venus, then Earth, then Venus again. This fortuitous and intricate trajectory, and its associated launch window enabled the probe to make the voyage, boosting its velocity enough to send it on a trajectory for Saturn.

The Interplanetary Trajectory

When the probe arrived in the Saturn system, it detached the Huygens lander on 24 December 2004. The Huygens lander landed on Titan on 14 January 2005. The probe successfully took and transmitted pictures of the surface, atmospheric and wind data, and even sounds from the surface of the moon.

Titan is a moon of Saturn, with a radius of 2580km (for comparison, our moon has a radius of 1700km and Mars has a radius of 3400km). When Voyager I first flew by this moon in 1980, it could not penetrate the hazy atmosphere to detect anything about the surface. The atmosphere of Titan is a dense smoggy layer of methane. Titan can maintain an atmosphere this dense because of its very low temperature, being far from the sun in the outer solar system.

A Comparison of the Sizes of the various Moons.


When Huygens landed, it found that Titan has a surface sculpted by liquid methane and other simple hydrocarbons. The planet looks superficially Earthlike, at least in black and white, with river deltas and lakes. But the rivers and lakes are methane and hydrocarbons, and the rocks are water-ice and nitrogen. Titan's surface has a temperature of about 94K (-290F).

Titan's sea from Huygens as it descends.


Color Image of Titan's Surface