Review of the year: Deep-space explorers make contact

Titan is the largest of Saturn's many moons, and the year began as it was visited by a spacecraft from Earth that landed a small probe on its frozen surface. The Cassini-Huygens spacecraft took seven years to travel the two billion miles to its final destination.

Last Christmas, the Huygens probe detached from the Cassini mothership and began its perilous final approach. In mid-January, its parachutes opened and Huygens floated down through Titan's atmosphere - it is the only moon known to have one - to touch down safely in a weird landscape etched by rivers of flowing methane.

"We are the first visitors of Titan. We shall unveil the secrets of this new world," said Professor Jean-Jacques Dourdain, director general of the European Space Agency.

Huygens was the brainchild of Professor John Zarnecki of the Open University, who admitted to feeling highly emotional when the box of scientific instruments arrived safely. "This is a tantalising glimpse of the processes at work on Titan," Professor Zarnecki said as data and images streamed back. "It shows how the weather systems operate, with methane-forming clouds and rain, producing the drainage channels, river beds and other features that we see in the images."

Six months later, the United States engineered an explosive encounter with the comet Tempel-1. Scientists fired a missile into the comet in an effort to examine the insides of these mysterious travellers. On 4 July, at 100 times the speed of a bullet, the missile slammed into Tempel-1, releasing the ingredients of the comet's primordial "soup". Nasa's Spitzer space telescope watched from afar, using its infra-red spectrometer to analyse the cloud of material ejected.

" We are assembling a list of comet ingredients that will be used by other scientists for years to come," said Carey Lisse of John Hopkins University. To their surprise, scientists found that comets contain a wide range of compounds, including aromatic hydrocarbons - organic substances found in the black soot on barbecues and car exhausts.

"Now we can stop guessing at what is inside comets," said Mike A'Hearn of the University of Maryland, the principal investigator for the Deep Impact mission. "The information is invaluable for piecing together how our own planets may have formed."

The Japanese weren't so lucky. Their Hayabusa probe was supposed to touch down on the Itokawa asteroid, pick up a sample and bring it back to Earth. The Japanese space agency announced on 26 November that its probe had touched down briefly, fired a projectile, collected the dust kicked up, and then lifted off again to transmit data.

However, it appears that the probe may not have collected any samples, and the space agency has said that it won't know for certain until it returns to Earth in June 2007.

Such are the risks of space exploration. Ask the scientists behind Cryosat, a satellite designed to monitor the Earth's polar ice. The £90m satellite was lost when its Russian rockets failed to lift it into the right orbit.

At least Europe's Venus Express mission launched safely in October. The spacecraft will study the runaway super-hot greenhouse effect on Earth's "evil twin" planet - perhaps helping scientists to understand what might happen here on Earth.