Cassini approaches Titanic flyby

Moment of truth for Huygens team

This time next week, the Cassini-Huygens spacecraft will be making its closest approach to Titan, Saturn's largest moon. The craft will come within 1,200km of Titan's surface, and space scientists are eagerly awaiting the data it will send back.

Launched in 1997, the Cassini-Huygens craft has travelled 3.5bn kilometers from Earth. It entered orbit around Saturn on 1 July this year, and has begun the process of collecting data on the planet and its moons, which will continue for the next four years. As it passes the moon, Cassini's instruments will scan for details of the moon’s interior structure, surface characteristics, atmospheric properties and interactions with Saturn’s magnetosphere.

The information Cassini gathers next week will be particularly useful for the European Space Agency's (ESA) Huygens team who will be using the data to check the accuracy of their atmospheric models. These have been developed for the separation, descent and landing of the Huygens probe.

Professor John Zarnecki from the Open University, lead scientist for the Science Surface Package on the Huygens Probe, says his team is looking forward to finding out how well his teams models fit the reality of the moon, and what kind of surface is under all the smog. "In other words we want to know if our instruments will land with a splash or a thud!"

The Huygens probe will separate from the main craft on Christmas day 2004 before heading to the surface of Titan, one of Saturn's many moons. It is scheduled to land on 14 January. Titan is particularly interesting to astronomers because it is thought to be very similar to the Earth before life emerged. Scientists speculate that the conditions could be right to produce amino acids, the building blocks of life, might be found.

The moon's atmosphere is composed mainly of nitrogen and methane. The methane is broken down by sunlight and forms other organic compounds: at least 12 have already been identified. These form a thick layer of smog, very similar to that on the early Earth. Althought it is a very cold body, scientists hypothesize that watery volcanos could erupt onto the surface, and could even remain liquid for long enough to convert the organic into amino acids.

Professor Michele Dougherty, from Imperial College, lead scientist for the Magnetometer instrument on Cassini said that the moon's similarities to the young Earth meant that data could start to unravel some of the mysteries of our own planet. She said: "The Cassini Magnetometer experiment will investigate Titan’s interior and variations in the magnetic field measurements could indicate the presence of an ocean contaminated by salty materials like in the Earth’s oceans and in the hypothesised oceans of Callisto and Europa in the Jovian System." ®

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