Carefully wrapped inside this donut-shaped bag is a 35-m diameter parachute about to be baked inside a specialised dry heater steriliser oven.

This 74 kg parachute, made mostly of nylon and Kevlar fabrics, will endure a six-minute dive into the thin martian atmosphere and slow down the ExoMars Rosalind Franklin rover for a safe landing on Mars. This feat will make it the largest parachute ever to fly on the Red Planet or anywhere else in the Solar System besides Earth.

The ExoMars Rosalind Franklin rover mission will launch in 2028 and spend over 25 months travelling to the Red Planet where it will search for signs of life under the martian surface.

The potential existence of past and perhaps even present-day life on our closest planetary neighbour requires rigorous sterilisation, to make sure that no microbes piggyback their way there from Earth. Any terrestrial microbes hardy enough to survive the ride through space would interfere with the investigation by causing ‘forward contamination’ and triggering a false positive.

But this is not the only reason why the parachute needs to be at least 10 000 times cleaner than your smartphone – protecting the martian environment from ourselves, in accordance with international planetary protection measures, is as important as protecting the mission.

To get rid of any microbes it might have picked up during its time on Earth, the parachute will be heated up in a specialised oven at the European Space Agency’s Life Support and Physical Sciences Laboratory at ESTEC, the agency’s technical centre in the Netherlands.

As step-by-step instructions on baking an ExoMars parachute are not readily available, the laboratory’s experts had to use its exact copies to identify the right parameters. Through multiple rounds of testing, they found that sterilising at 125°C for 36 hours – following a 50-hour preheating procedure to make sure even the innermost parts of the parachute reach that temperature – results in a parachute clean enough to meet all planetary protection requirements.

Until now, the process might have resembled baking a cake in your kitchen – but this is where the similarities end. Unlike your oven, ESA’s dry heater steriliser is located in an ‘ISO Class 1’ cleanroom, one of the cleanest places in Europe. All air inside the room continuously passes through a two-stage filter, and everyone entering the chamber has to gown up more rigorously than a surgeon before passing through an air shower to remove any contaminants.

After coming out of the oven, the parachute was given a few hours to cool down before the lab team suited up and carefully packaged it inside the cleanroom. Once sealed inside a protective wrapping, the squeaky-clean parachute was sent back to its makers at Thales Alenia Space in Turin, Italy, where it awaits spacecraft integration.

Last year, a precise copy of the parachute was deployed during a high-altitude balloon drop test, successfully slowing down an ExoMars mock-up landing platform for a safe touchdown on Earth.

Watch ESA’s Mars chief engineer Albert Haldemann explain the baking process and why it is a big step for the ExoMars Rosalind Franklin rover mission.