John Zarnecki, professor of space science at the Open University, is to spend yet another Christmas worrying about an interplanetary probe. Last year it was Beagle 2 , now it's Huygens , which is due to separate from its mothership Cassini on December 25 and will head for a rendezvous with Saturn's mysterious moon Titan three weeks later. But Professor Zarnecki, principal investigator with Huygens ' surface science package, said he'd been devastated when Huygens was approved in 1988 at the expense of a proposal he'd been working on for 12 months. So perhaps there was an element of revenge when Professor Zarnecki explained that his dream scenario was to watch a giant wave bearing down as Huygens floats helpless on some notional sea.