In science-fiction circles, there was excited chatter last week about online trailers for Ambition. This slick short film depicts humans in the distant future — somehow imbued with the power to craft their own worlds — discussing how they discovered the key to life.

The film, directed by Oscar nominee Tomek Bagiński and starring Aidan Gillen from the television show Game of Thrones, was not what it seemed. It was the work of the European Space Agency (ESA), using the film as a Trojan Horse to trick an unsuspecting public into engaging with science. The fictional secret to life, the full film revealed, was unearthed with the help of Rosetta — a real ESA mission that this week plans to land a probe on a real comet.

The goal of the mission is more modest than in the film: it hopes to find clues as to whether ancient comets could have delivered Earth’s oceans or even the organic molecules that sparked life. Although this is a fascinating puzzle, it is unlikely to be the feature of the mission that people remember. The real drama is the high-stakes attempt to land a probe on the 4-kilometre-diameter comet — 67P/Churyumov–Gerasimenko — which is travelling at more than 60,000 kilometres per hour some 500 million kilometres from Earth. The lander was due to be released, and its fate learned, soon after Nature went to press.

The lander, Philae, is intended to provide a ground truth with which to cross-check measurements from the Rosetta orbiter. But it is also designed to go beyond the orbiter’s instruments, using an on-board laboratory to analyse samples from 20 centimetres beneath the comet’s surface (including materials that would not make it to the dusty tail) and by studying its mechanical properties and interior.

Missions have flown to comets before. Whereas ESA’s Giotto and NASA’s Stardust provided snapshots, sampling the tail of comets as they raced past at high speed, Rosetta has stalked its prey at close range. Landing the Philae probe was always going to be the riskiest part of the mission. NASA’s Deep Impact mission deliberately crash-landed a probe on the surface of a comet to unearth pristine dust for its parent craft to study, but this soft landing is a first.

ESA flight managers say that this is the most ambitious mission they have ever flown.

Unlike asteroids, comets are active bodies that send out streams of water, gas and dust. Rosetta must navigate the harsh environment with sufficient delicacy and precision to launch the lander into a 1-square-kilometre patch on the comet’s surface, some 20 kilometres away. Philae must land with a gentle bump, travelling at just 1 metre per second. The slow descent is crucial because the comet’s gravitational pull is several hundred thousand times weaker than that on Earth. Even a safe landing is not the final act; the craft must deploy harpoons and ice screws to tie itself to the comet’s unforgiving surface.

Experienced ESA flight managers say that this is the most ambitious mission they have ever flown. In terms of complexity, it is more like Apollo 11’s landing of humans on the Moon than a Mars adventure. And it is being done with 20-year-old, space-hardy technology, the processing power of which is more like that of a pocket calculator than anything recognizable on a desktop today. Two decades in the planning (and a decade in transit), the Rosetta mission was developed after NASA cancelled its own Comet Rendezvous Asteroid Flyby mission. The Europeans built on NASA’s plans, but instead of a probe, went for the (perhaps more risky) soft-landing option.

Rosetta was always going to be flying into the unknown. All that was known about the comet was its size and orbit around the Sun. Only when it arrived, and discovered 67P to be a bizarre, rugged, rubber-duck-shaped comet rather than the potato the mission scientists were expecting, did the team begin to work out where best to set down the lander.

Rosetta is also a mission of endurance. For a decade, the craft has been chasing its comet through the Solar System, including the cold of space beyond the asteroid belt, for which it was designed to survive temperatures as low as −180 °C.

There are lots of ways the mission could (did?) fail, all of which are illustrated in a graphic on page 172. The final manoeuvre ahead of separation, which sets the lander up with the speed and trajectory for its unpowered descent, must go off without a hitch. The craft and lander must separate in perfect synchrony. And then there is luck. Even if Rosetta performs perfectly and mission scientists do everything right — as has been the case so far — if Philae were to land on a cliff, ridge or boulder the probe would topple, and it could be game over.

ESA scientists are not just covering their backs when they say that the mission will be a success whether or not Philae lands safely. Whatever happens to the lander, Rosetta will continue orbiting the comet, the first spacecraft to take a ringside seat as a comet changes in its approach to the Sun. Landing may be the high-drama part of the mission, but around 80% of the science output is expected to come from Rosetta.

Philae’s fate might dictate Rosetta’s public legacy, but all scientists should celebrate the mission’s attempt — whether in homage to its triumph or memorial to its loss — for the engineering and technical expertise it took to execute.

In attempting to capture the public’s imagination by stealth, Ambition was somewhat out of character for ESA or, indeed, any public research body. But the film — which must have cost a large chunk of the mission’s public-relations budget — was probably unnecessary. The feat alone is spectacle enough.