It would be the most audacious and technologically challenging space mission since the Apollo programme landed Neil Armstrong and Edwin "Buzz" Aldrin on the moon in 1969. An international team of scientists has put together detailed plans for a mission to bring back samples of rock, and possibly microscopic life, from the surface of Mars.

To be successful the mission, which is proposed for launch between 2018 and 2023 and could cost up to $8bn, would require expertise and funding from both Nasa and the European Space Agency, as well as other national space agencies. "This is going to be extremely expensive and no one space agency can afford it," said Professor Monica Grady, at the Open University, who co-chaired the expert panel that wrote the mission proposal.

She said it was a vital next step before a possible crewed mission to the Red Planet. "If you can't bring a rock back you are not going to be able to bring people back. There's a real feeling that bringing samples back from Mars is absolutely essential if we are going to continue our Martian exploration programme."

Sending people to Mars will probably not be possible before 2050, but if a crewed mission were ever to go ahead scientists and engineers would need to demonstrate that it is possible to land a craft on the surface of Mars and bring it back to Earth safely. There have been seven successful landings on the Red Planet since the US spacecraft Mariner 4 flew past Mars for the first time in 1965, but no lander has ever taken off from the surface again or brought anything back to Earth.

The mission proposal is the result of an eight-month study by 31 scientists from around the world.

Grady and her colleagues presented it to delegates at a conference of the International Mars Exploration Working Group (IMEWG) in Paris last week. The group is made up of delegates from national space agencies and puts together plans for future missions. The heads of both Nasa and the ESA have received copies and the two agencies will decide in November whether to fund the mission's next planning stage. To hit the proposed timescale, technology development for the mission will need to begin by 2011.

Professor Colin Pillinger, at the Open University, who led Britain's unsuccessful Beagle II mission to Mars in 2003, said returning samples from the Red Planet would allow scientists to carry out much more sophisticated analyses on the rocks and permit a more detailed search for simple Martian life forms. "Everybody knows this is what you have got to do if you want to really get to the bottom of Mars," he said. But he said avoiding contamination would be extremely difficult.

"There's a big caveat when you start playing with Mars, and that's planetary protection. You have to be very careful not to bring anything back that might be harmful to Earth," he said. "Your mission has to be guaranteed, and I really mean guaranteed, to get into the Earth's atmosphere without damaging itself."

If Martian microbes do exist they must be extremely hardy, having survived the planet's freezing, desiccating surface and bombardment with UV radiation, so if the returning spacecraft blew up on re-entry scientists could not be sure that Martian life forms on board would be destroyed in the blast. It would also be impossible to know what they would do to life on Earth. Although samples have been returned successfully from space by robotic vehicles, the first attempt to bring samples from beyond the moon ended disastrously. The Genesis probe, which carried particles collected from the solar wind, crash landed in the Utah desert in September 2004.

The mission would involve the launch of two separate craft from Earth - a "lander composite" and an "orbiter composite". Both would make the trip to Mars, where the lander would touch down on the surface. It would then release a rover which would collect a variety of rock samples totalling around half a kilogram.

It would bring these back to the lander, where the rocks, plus a sample of Martian atmosphere, would be encased in a sealed pod within the so-called Mars Ascent Vehicle - part of the lander composite. This would then blast off from the surface and dock with the orbiter before transferring its precious cargo. The orbiter would then return to Earth, enter the atmosphere and land. At this point, scientists would rush in and transfer the samples to a top-level biosecurity lab, where they would be analysed for any possible signs of life.

Scientists have long fantasised about the possibility of bringing back rocks from the Red Planet. But the backing of IMEWG is a significant boost for the current plan.

They have also been emboldened by the success of several recent missions to Mars, including Nasa's Phoenix lander, which touched down in May. If the mission is to get off the ground, though, it will need strong political backing both in Europe and from the incoming US president, said Pillinger.

Martian chronicles: Previous missions

After a string of failures in the early 1960s by both the Soviet Union and the US, Mariner 4 in July 1965 became the first spacecraft to fly past Mars and send back images.

Following other successful flybys, Nasa orbited Mars in November 1971 for the first time with Mariner 9. The orbiter mapped 80% of the planet's surface by taking 7,329 images.

The Soviet Mars 3 mission was the first to successfully land on the planet in December 1971. It was severely damaged in a Martian dust storm, though, and sent back just 20 seconds of data.

Nasa's two Viking missions, which arrived at the Red Planet in 1976, landed successfully and transmitted more than 50,000 images. Nasa's Mars Pathfinder mission, pictured, which touched down in July 1997, was the first successful rover to probe the planet.

The European Space Agency's Mars Express mission reached Mars in December 2003 and is still operational. But its cargo, the British-led Beagle II lander, crashed on Christmas Day 2003 and failed to send back any data.

Nasa's successful Spirit and Opportunity rovers arrived on Mars in January 2004 and are still operating. The latest lander, Nasa's Phoenix mission, touched down in May this year.