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A space probe crashes in the desert. Something deadly on board wipes out almost the entire population of a small town. The government instigates an emergency protocol and top scientists gather at a secret underground quarantine facility to contain this killer germ from outer space.

Will they be able to save the planet from disaster?

To find out, read Michael Crichton’s Andromeda Strain – an adventure with heroic scientists. This terrifying tale of alien microbes, bringing instantaneous death to (almost) every living creature they come into contact with, was published weeks before the first Apollo lunar landing. But Nasa had already predicted this worst-case scenario of bringing back material from another world.

On their return to Earth, the Apollo 11 astronauts were locked away in a converted Airstream caravan - the Mobile Quarantine Facility. Lunar rocks and soil were sealed in bags and only opened in airtight laboratories. Even the Apollo capsule was wiped with bleach to destroy any stray Moon bugs. In retrospect, these precautions look rather quaint and the whole rigmarole was abandoned after Apollo 14, when scientists concluded that the Moon was completely devoid of life.

But now, 40 years on, Nasa is dusting down those quarantine procedures for a new challenge: returning rocks from Mars.

A so-called Mars sample return mission is the next step in the exploration of the red planet, coming between the existing rover missions, such as Curiosity, and future human exploration. It may also, finally, answer one of the biggest questions about Mars: is there life?

“The Curiosity rover does not have the instruments to answer the ‘are we alone’ question by itself,” says David Beaty, chief scientist for Nasa’s Mars Exploration Directorate at the Jet Propulsion Laboratory in Pasadena, California. “All it can do is understand the environment. Testing for ‘is there evidence of life?’ requires another mission and the best way to do that is by collecting samples and returning them to Earth.”

Popping out for coffee

The reason scientists favour a sample return mission is that they do not know exactly what they are looking for. Martian life could come in many different guises and using equipment designed to detect life on Earth, may not pick it up on Mars. Nasa could design another rover, equipped with all sorts of life-hunting instrumentation, only to find it is taking the wrong measurements with the wrong detectors. 

“If you have the wrong experiment on your rover, you can’t modify that,” says Beaty’s Mars programme colleague, Deborah Bass. “If you bring samples back, you have all the power of Earth’s laboratories at your disposal.”

But it won’t be easy. Although robotic sample return missions have been attempted before, they have had varying degrees of success. The first, Luna 16, landed on the Moon in 1970 and brought the Soviet Union back its own lunar rocks. In 2004, Nasa’s Genesis mission returned to Earth after capturing particles blown from the Sun. Unfortunately, the spacecraft’s parachutes failed to open and it smashed into the Utah desert spilling its contents. Nasa had more luck in 2006 with its Stardust mission to a comet but things did not go so well for the 2010 Japanese Hayabusa mission, which returned to Earth after landing on an asteroid. It only managed to capture a few dust particles, as projectiles designed to blast fragments from the surface failed to fire. No mission has yet returned samples from another planet.

Still, the good news is that they do not need to collect much. Whereas Apollo brought back several hundred kilos of rocks, soil and dust, Beaty reckons he would be happy with 20 Mars samples of some 15g to 20g each – between 300g and 400 g in total. Or, to put it another way, “what would fit in a coffee cup”.

Although as you can imagine, adds Bass, there is a little more to it than that. “If we just go to a random location on Mars and started tossing things into a coffee cup, it’s unlikely we would find what we are looking for.”

Plans for a sample return mission are still on the drawing board but most envisage a spacecraft landing a rover (or even several small rovers) in an area where life might have hung out. Probably a place where there used to be flowing water. Once safely on the ground, the rover will trundle off to collect soil or rock from a number of key sites, digging or drilling into the Martian dirt. It will then return to the lander to load its samples into a coffee-cup-sized capsule. So far, so straightforward – and certainly achievable with existing robotic technology.

The most crucial part of the mission, the sample return stage, is a lot harder. Nasa’s current concept employs a rocket – built into the lander – to launch the capsule from the Martian surface into Mars orbit. Here, it docks with a mothership. This spacecraft then fires its engines and heads back towards Earth. As the sample return spacecraft approaches our planet, it will use parachutes to survive a 50,000 km/s (30,000 mph) plummet and descend gently to the ground (or sea) for recovery.

Mission planners are well aware that docking with a spacecraft while in orbit around another planet has never been attempted before nor has bringing that spacecraft back to Earth. But assuming all goes to plan, the idea is that the samples will be recovered from the capsule and whisked away into a “secure containment facility.”

The technology being looked at for this laboratory is based on existing secure biological or nuclear facilities, incorporating the lessons learnt from Apollo. The aim of quarantine is not only to prevent any risk from Mars germs – and some horrible Andromeda Strain scenario – but the contamination of Mars samples by Earth microbes. Although the chances of the sample containing a deadly bug are almost certainly miniscule, the consequences of any release are potentially serious. What if there really was a deadly bug on Mars? However remote the possibility, we would be foolhardy to rule it out. It is therefore essential that, unlike the Stardust mission, the container survives its return. 

The mission’s success is also vital for Nasa’s plans beyond sample return: a human mission to Mars, currently slated for 2033.

“Mars sample return has a second very important purpose: to demonstrate a rocket that can leave Mars,” Beaty explains. “If you can’t demonstrate you can return a rock from Mars, how can you believe you can return a human?

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