Touch down on Titan

Titan Artist's impression of the Huygens probe entering the upper layers of Titan's atmosphere. Copyright ESA-D/DUCROS

Professor John Zarnecki, Mr Mark Leese, Mr Brijen Hathi, Dr Andrew Ball, Dr Axel Hagermann, Dr Martin Towner, Professor Tony McDonnell, Dr Simon Green, Dr Manish Patel, Dr Timothy Ringrose, Mr Philip Rosenberg, Mr Karl Atkinson and MrMark Paton. 
The Open University. 

On 14 January 2005 John Zarnecki and colleagues at the Planetary and Space Sciences Research Institute (PSSRI) waited with bated breath to discover whether the Huygens probe would arrive at Titan with a thud, squelch or splash. No-one knew what the surface of Titan, Saturn's largest moon, would be like and whether the probe would land on wet or dry ground and survive the landing. At 2pm the team discovered that Huygens had made it to the surface of Titan intact. By the early hours of the following day the data received from the Surface Science Package (SSP) was described as 'exceeding their wildest dreams'; the team had hoped for 3 minutes of data from the surface and had received 70. Early analysis of the data is providing the first ever glimpse of what the surface of Titan is really like. 

Titan, discovered by Christiaan Huygens in 1655, is the only moon in our solar system with a substantial atmosphere. Just like Earth, Titan's atmosphere is mostly nitrogen along with methane and many other organic compounds. On Earth, methane in the atmosphere is a clear sign of life, but life on Titan seems unlikely, as the surface temperature is estimated to be 180°C. These similarities to Earth mean that data gathered on Titan's surface structure and atmosphere could provide insights into how life began on Earth. 

Data from the SSP suggest that Titan's surface is covered in channels or rivers carved out of icy bedrock by methane rain, and these are clearly visible on the images received from Huygens. 'Much like our rivers carve out channels by grinding rocks into sand or gravel, on Titan the methane rain grinds up the ice creating smaller particles that are then washed down into lakes or small seas', explains John. 'The most likely scenario  from the data we received is that on landing the SSP hit a pebble-like object and then ploughed into the Titan equivalent of sand so I guess the landing was a gentle thud'.