The European Space Agency's parlous finances are jeopardising its best chance to launch a mission to Mars for a generation. Julia Hinde reports.

Either Europe goes to Mars with Mars Express, or it can forget all about planetary science." The reality is painfully simple, at least in the eyes of Colin Pillinger, professor of planetary science at the Open University. If Europe wants to play a role in investigating other planets, and ultimately in the search for extra-terrestrial life, however basic it may turn out to be, then it must sign up to the next planned space mission. Otherwise, it will be a question of sitting back and watching the Americans.

Scientists say 2003 presents a perfect opportunity for reaching Mars. The relative positioning of the planets opens a window of opportunity, which will not occur again for another decade. Scientists across Europe have embraced the idea of a mission to Mars, five years from now, funded by the European Space Agency. They have proposed more than 30 different instruments that could be included on a rocket called the "Mars Express". The instruments include a landing craft, Beagle 2, championed by Professor Pillinger.

The science being proposed is, according to many, excellent, but ultimately it is funding and politics that will determine whether the Mars Express blasts off. These two factors, inextricably linked, are jeopardising Europe's hopes of a mission to the Red planet.

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When the ESA first proposed Mars Express in April 1997, its suggestion was greeted with hostility by some scientists. They feared that the mission would "gatecrash" the established ESA routine of competitive bidding for funding to pay for specific scientific projects. But, spurred on by widespread public interest in the Red planet as a result of Nasa's claims to have found evidence of life in a Martian meteorite, the space agency went ahead with a call for research bids from scientists.

The agency proposed to pay the Pounds 123 million needed to build and launch the mission, but it would be up to individual European countries to pay for instruments. If Pillinger and his team wanted to send Beagle 2 to Mars, not only would they have to prove its scientific worth, but also find up to Pounds 25 million, either from the already stretched British science budget or privately.

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A year on, Beagle 2, named after Charles Darwin's ship, is expected to be the only landing craft considered for Mars Express. Other instruments, for measuring atmospheric loss or photographing the planet's surface, will compete for space on the orbiter, while Pillinger's team hopes to land Beagle 2 and dig beneath Mars's dust and rock for signs of life.

According to Monica Grady of the Natural History Museum, who is working with Pillinger, it is only under the planet's surface that we are likely to detect life. Mars's atmosphere today is very thin and the ultraviolet radiation from the sun would be death to any carbon bonds (which form the base of organic material) on the surface of the planet. "If we want to look for things still living, we have to be looking in caves, rocks and underground," says Grady. Beagle 2 will contain a mechanical mole which will feed its spectrometer with rock samples from up to two metres below the surface.

In order to be ready for 2003, ESA's scientific committee is expected to decide which instruments it supports at a meeting this month, with a final decision on the project in November. Pillinger has presented his plans and is now pushing for extra time. He says he is in a chicken and egg situation. Though he hopes government money can be found for the lander after the government's ongoing spending review, he has found it difficult to secure private funding without knowing that his project has been selected by ESA. ESA, on the other hand, is likely only to select instruments which can be funded. "We want the agency to say that we are scientifically and technically acceptable and then let us go and raise the money," says Pillinger.

But there now appears to be an even greater financial barrier to Beagle 2 making it to Mars. At a meeting in London earlier this month, Roger Bonnet, ESA's scientific director, said that if ESA's financial situation remains as it is, then ESA will need to rethink its priorities. In 1995, ESA member states put a cap on agency spending, fixing subscriptions over the following three, and possibly five, years. The cap, imposed in a bid to force greater economies at the agency, was to be reviewed this year. As one space scientist says: "ESA is using Mars Express as a carrot to make member states rescind the cap from this year onwards." He adds: "It looks very unlikely this strategy will work."

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ESA's science committee will have to decide in November - almost certainly without more money - whether it can afford Mars Express. Paul Murdin, a member of the committee which will make the final decision, says: "In November it is doubtful we will know more about levels of resources than now, except that there is no hope of lifting the cap in the fourth year. Therefore, if we hold to logic, ESA can't do Mars Express." But he adds: "I think that by comparison with previous missions, Mars Express is amazingly good value. There may be other areas for manoeuvre."

Others note the very strong scientific interest in the project. Ken Pounds, former chief executive of the Particle Physics and Astronomy Research Council, and himself a space scientist, says that the best way for ESA to win more money in the long run is to demonstrate cost effectiveness. "I hope ESA doesn't retreat from the challenge," he says.

Fifty-five-year-old Pillinger, who has dedicated his academic life to looking for life beyond Earth, says: "Mars Express will happen. I am prepared to go up to the wire to see if I can get on board."