It must be tough right now being a UK scientist involved in the Cassini spacecraft mission to Saturn and its moons.

It must be a bit like being told all your friends are going to the party but you're staying behind.

The US space agency has just approved a further and final extension to the Saturn probe's mission. The extension will enable observations to continue until 2017, when the spacecraft will be commanded to plunge into the ringed planet's atmosphere.

It will be a spectacular ending to an extraordinary adventure at everyone's second favourite planet (after Earth).

For British planetary scientists, however, this news is bitter-sweet because they were told before Christmas that the funding which supports their operational work is stopping.

Cassini is not the only space project which is about to see the UK execute a "managed withdrawal".

British effort on the Sun-Earth system missions Cluster and Soho will be curtailed also; so will support for Venus Express and the X-ray telescope XMM-Newton.

The Science and Technology Facilities Council (STFC), the body that directs funding for physics and astronomy in the UK, is in something of a bind - to put it mildly.

It has structural problems and is also struggling with the depressed value of the pound, which makes the subscriptions it pays to belong to international organisations, such as the European Space Agency, very expensive.

The STFC is trying to save tens of millions over the next five years, and it has identified ongoing Cassini support as a low priority.

The present round of UK funding for the mission runs to 31 March, but just pulling the plug on this date would amount to a "dump and run" policy rather than managed retreat.

So discussions are going to take place with international partners to determine how Britain can best extricate itself from its commitments, and over what timescale.

The scientists themselves will be hoping they can hang in there for as long as possible.

The British contribution to the mission has been immense. It has co-investigators on many of the instruments and the principal investigator on Cassini's magnetometer - Prof Michele Dougherty from Imperial College London.

It was the magnetometer, you will recall, that was responsible for making what is unquestionably one of the big discoveries in space science in recent years - the atmosphere at the moon Enceladus.

Cassini has a lot of unfinished business at the ringed planet and it will undoubtedly make many more remarkable observations.

When the probe arrived in 2004, it did so in the depths of the northern winter, when the southern poles of the planet and its moons were in direct sunlight.

Nasa's decision to extend the Cassini mission to 2017 means scientists will now be able to see the system until a few months past the northern summer solstice.

What effects will the change of seasons have?

As the shadow cast by the rings moves across Saturn's clouds, how will the atmosphere react? Will some of the methane lakes that dominate the northern pole of Titan evaporate? Is it possible the giant plumes on Enceladus could wilt? There are so many questions.

The Cassini spacecraft itself is in excellent health and when I spoke a few weeks ago to Bob Pappalardo, the Nasa Cassini project scientist, he was relishing the tasks ahead:

"We've got a lot of exciting stuff coming up. We've got a daring fly-by of Titan in 2010. It's the lowest we'll go into the atmosphere - about 880km. The goal is to dip below some of the ionospheric effects and try to tell whether there is an intrinsic magnetic field at Titan."

The fly-by will be a high priority for the magnetometer instrument, of course. It means Prof Dougherty's team at Imperial will once again be in the driver's seat.

The observations will go a long way to resolving the debate over whether the moon has a convecting liquid core or not.

British Cassini researchers will have to wait on the outcome of those discussions with international partners before they will know how long their participation in the mission will be maintained.

The worry in situations like this is that withdrawal will harm not only present endeavour but our involvement in future missions as well.

If our young scientists today are not working on Cassini, they will not be in a position to command prominent roles on the next flagship visit to the outer planets, such the proposed Europa-Jupiter System Mission (EJSM) in the late 2020s.

With space funding already under pressure and all the main political parties promising to keep a tight rein on post-election public spending, it's clear that British planetary scientists, like almost everyone else, may face some tough times ahead.