Nasa and Esa have signed a letter of intent that could lead to the first “round trip” to another planet.

The move was announced as a meeting in Berlin, Germany, discussed the science goals and feasibility of a Mars Sample Return (MSR) mission.

The venture would allow scientists to answer key questions about Martian history.

Those questions include whether the Red Planet once hosted life.

Scientists at the Mars meeting said that there was only so much they could learn from Martian meteorites and from the various rovers and static landers sent to the Red Planet.

The next step had to be a mission that would retrieve samples from the Martian surface, blast them into space in a capsule and land them safely on Earth.

They could then be subjected to detailed analysis in laboratories, using instruments that are currently too large and power-hungry to carry as part of a robotic rover’s payload and techniques that are difficult to perform from 55 million kilometres away.

Making the announcement at the ILA Berlin Air and Space Show, which is taking place at the same time as the Mars science meeting, Dr Thomas Zurbuchen, Nasa’s associate administrator for science, said: “We want to partner with the European Space Agency, but also with other partners.”

He said this included potential link-ups with the commercial space sector, adding: “We will at every point look at what is available in the commercial market. Nasa has no interest whatsoever in developing things that we can buy.”

Dave Parker, director of human and robotic exploration at Esa, commented: “It’s very important that every mission we send to Mars discovers something slightly unusual. It’s on the basis of that that we tend to plan the next mission or next missions.”

Nasa’s 2020 rover mission is expected to help pave the way for Mars Sample Return, by drilling into the surface and caching the cores in containers. But this is designed principally to act as a demonstration.

The design of a sample return mission would need to be drawn up in coming years. Previous concepts have envisaged a rover storing the geological samples from scientifically desirable locations on Mars.

The cached samples would then be loaded on to an ascent vehicle which would lift off from the Martian surface. After the cruise back to Earth, a descent module would parachute down through Earth’s atmosphere, delivering the first retrieved Martian samples directly into the hands of experts waiting on the ground.

Protecting the planet

If life existed in the past on the Red Planet, it would likely have been microbial in nature. Today, the high levels of cosmic radiation on Mars’ surface – a consequence of its thin atmosphere – would create a hostile environment for any organisms.

But in the unlikely scenario that organisms are living in the Martian soil today, the mission itself and the handling of samples once they arrived on Earth would need to be subject to strict quarantine, or “planetary protection”, procedures aimed at preventing the contamination of Earth’s biosphere with any Martian bugs.

Dr Zurbuchen said the sample return mission could also be crucial for later planned human exploration of Mars, which he said Nasa should start thinking about in the 2030s.

“I can imagine a lot of scenarios where the samples are actually critical for how we explore as humans,” he said.

Esa’s Trace Gas Orbiter (TGO) is currently commissioning its instruments in Martian orbit. It will contribute to the life question by mapping the distribution in the atmosphere of methane gas, which could be produced by Martian organisms, but also by non-biological sources.

Nasa and Esa had previously worked together on a programme to return geological samples from the Red Planet. In 2009, the agencies agreed to collaborate on the Mars Joint Exploration Initiative, which would have culminated in the recovery of samples in the 2020s.

But in 2011, Nasa cancelled its participation in the project amid a budgetary squeeze.

The 2nd International Mars Sample Return Conference is taking place from 25-27 April 2018 in Berlin.