"We'll be looking at the best solution for getting there and back," UK Astrium's Dr Ralph Cordey told BBC News.
"We've got to look at all elements of the mission - how we would design the mission, how to design the trajectory to one of a number of possible asteroids, how to optimise that so we use the smallest spacecraft, the least fuel and the smallest rocket."
Marco Polo might work like this:
• After the launch on a Soyuz rocket from Europe's Kourou spaceport, a propulsion unit would take the mission out to its target asteroid
• The main spacecraft unit would undertake a remote-sensing campaign, gathering key information on shape, size, mass, spin and global composition
• It would then attempt to land, drilling a few cm into the surface. Up to 300g of dust and pebbles would be stored away in a sealed capsule
• After lifting off the asteroid, the spacecraft would put itself on a homeward trajectory, releasing the capsule close to Earth for a re-entry
• The capsule would land without parachutes. It would be opened in a clean facility to ensure there was no Earth contamination
Marco Polo would map the asteroid as well as grabbing a sample
Esa has an exploration roadmap for the missions it wishes to conduct in the coming years. Marco Polo is being considered under its Cosmic Visions programme, and is one of a number of competing ideas in a class of missions that could cost in the region of 300 million euros.
It is quite possible that Marco Polo, if approved, could be undertaken in partnership with Japan.
Sample return missions are of significant interest to scientists. Although in-situ measurements provide remarkable insights, so much more would be learnt if materials were brought back to Earth laboratories, where the full panoply of modern analytical technologies can be deployed.
The small return capsule would be released just prior to re-entry
An asteroid sample return mission would have huge scientific merit in its own right but it would also help develop the technology needed for the more challenging task of getting down and up from a large planetary body that has a much bigger gravitational pull - such as Mars.
Not that getting down on to a small, low-gravity body is easy. The wrong approach could crush landing legs or even result in the vehicle bouncing straight back off into space.
Such problems were amply demonstrated by the recent Japanese attempts to grab samples off the surface of Asteroid Itokawa.
It is still not clear whether Japan's Hayabusa spacecraft managed to capture any material and the probe's return to Earth is still haunted by uncertainty.
The Americans deliberately crash-landed their Near-Shoemaker probe on to Asteroid Eros at the end of the spacecraft's mission in 2001.
They have also sent the Dawn spacecraft to rendezvous with Asteroid Vesta in 2011 before going on to visit Asteroid Ceres in 2015. But these are remote-sensing ventures, not sample return attempts.
Europe, itself, is no novice in the field of asteroid study. Its Rosetta probe, which is en route to a comet, took close-up pictures of Asteroid Steins during a flyby earlier this month.
Ultimately, it is possible that astronauts could visit an asteroid. The US space agency is currently studying how this might be done; but even if approved, such a mission would not happen for many decades.
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