Five years ago the European Space Agency's (ESA) Huygens Probe made history when it landed on Titan, the largest moon in the Saturnian system. The touchdown on the surface of Titan marked the first, and so far only, landing of a man-made probe in the outer Solar System.

Today many of the scientists and engineers that worked on the mission will celebrate this anniversary in the science museum Cosmocaixa in Barcelona, Spain.

They will share their memories with the public and reveal future projects, "much work remains to be done", says ESA's Huygens Project Scientist Jean-Pierre Lebreton, "Titan has many different environments to explore further with in situ probes".

The international Cassini-Huygens mission to Saturn was jointly developed by NASA, ESA and the Italian Space Agency (ASI). The Cassini-Huygens spacecraft, consisting of NASA's Cassini orbiter and ESA's Huygens Probe was launched on 15 October 1997. After six and a half years of interplanetary voyage Cassini-Huygens went into orbit around Saturn, and on 25 December 2004 the Probe was released on a ballistic trajectory to Titan.

On 14th January 2005 the Huygens Probe made an historic journey through Titan's hazy atmosphere carrying a suite of six scientific instruments that performed measurements and obtained images during the decent. Following a gentle landing the Huygens Probe continued to function for several hours with the six instruments performing well. The successful landing of the Huygens probe on Titan pushed the frontiers of exploration forwards, to the realm of the outer Solar System.

"I remember it very vividly, it was a very intense moment", says Alvaro Gimenez Canete, ESA Science Policy Coordinator and Director of the Spanish Centre for Astrobiology.

"We didn't even know whether Huygens would survive the impact. We didn't know then if the touchdown would be on a solid surface or in a sea. Then, when the first pictures arrived, I was struck by the apparently strong similarities with Mars or even the Earth: Titan had a ground, rocks.... Of course we soon learnt that it is very different from Earth, a fascinating cold world in which methane plays the role of water on Earth".

Five years ago Gimenez was in Darmstadt, Germany, witnessing the event from ESA's European Space Operations Centre (ESOC) and is now participating in the celebration to mark the fifth anniversary of this remarkable event at the Huygens Legacy and Future Titan Exploration conference, which will run for three days from 13 - 15 January 2010.

The conference will cover a broad range of topics including science results from the Huygens in situ exploration of Titan, results from studies of this moon using remote sensing from instruments on the Cassini Orbiter combined with Huygens data, and the role of ground-based observations, laboratory data and modelling in interpreting the observations of Titan from space.

Data returned by the Huygens Probe have provided a unique view of Titan and have led to a wealth of surprising discoveries. As Gimenez noted, "In many ways Titan resembles the Earth", explains Lebreton.

"Both have atmospheres that are predominately nitrogen gas. Titan's unique atmosphere contains 1.5% methane and no oxygen. The surface pressure on Titan is 1.5 times that at the surface of the Earth. There are aerosol layers and clouds that come and go. Huygens discovered that the surface of Titan looks much like the surface of the Earth, with terrestrial analogues for many of the landscapes. Whether it be fluvially carved surfaces with networks of stream and river channels, lakes (some of them dry), impact craters, possible lava flows, or sand dunes - these are all familiar features on the Earth. This suggests that similar processes operate on both surfaces. However, the big difference at Titan is the very cold temperature. Water-ice plays the role of rock and liquid methane plays the role of water".

Due to a smooth landing on Titan the Huygens probe survived for longer than anticipated and only ceased to operate once the onboard batteries had no power remaining. The Cassini Equinox Mission, which commenced 1 July 2008, is continuing the tour of the Saturnian system, including further flybys of Titan. In addition the Cassini Equinox Mission will monitor the seasonal effects on Titan and Saturn "We expect seasonal effects on Titan too", says Dennis Matson, Senior Research Scientist Titan and Saturn System Mission (TSSM) Jet Propulsion Laboratory (Caltech).

"Will the size and number of the lakes in the South grow as winter comes? Shall we see the northern lakes and seas diminish or dry up as summer progresses?".

"The amazing discoveries have redefined our concept of the whole system. We are seeing many features and processes for the first time. Some of them are beautiful, some astound us, and others tax our abilities of explanation", write both Matson and Lebreton.