Water vapour has been detected escaping from Mars’s atmosphere, offering scientists a fresh clue as to whether the red planet was once home to life.

The ExoMars Trace Gas Orbiter (TGO), operated by the European Space Agency (ESA) and Russia’s Roscosmos, made the discovery by measuring light as vapour passes through the atmosphere.

Scientists, including two from the Open University, used an instrument on board the orbiter called the “Nadir and Occultation for Mars Discovery” (NOMAD) to study water vapour and “semi-heavy” water.

As hydrogen chloride gas rises, it gives researchers an indication of the history of water on Mars.

The red planet features several ancient dried out valleys and river channels which have long pointed towards the possibility of liquid water once flowing there.

Understanding water vapour on Mars would help answer the all-important question, was there life on Mars?

Much of it is now locked up in the ice caps and buried underground.

Dr Manish Patel, co-principal investigator of NOMAD, said: “The NOMAD instrument is fundamentally changing our understanding of the evolution of water on Mars.

“This fantastic instrument is giving us a never-before-seen view of water isotopes (water variants with different molecular masses) in the atmosphere of Mars as a function of both time and location on Mars.

“Measuring water isotopes is a crucial element of understanding how Mars as a planet has lost its water over time, and therefore how the habitability of Mars has changed throughout its history.”

As well as helping scientists understand the workings of a Martian water cycle, the findings also provide signs of magmatic activity.

Sue Horne, head of space exploration at the UK Space Agency, said: “This research is a key component in our quest to unearth the mysteries of the Red Planet.

“Understanding water vapour on Mars would help answer the all-important question, was there life on Mars?

“UK scientists and technology are playing a leading part in Nasa’s Perseverance rover mission due to land on Mars this month.

“The mission will collect samples from the planet’s surface to further our understanding of our neighbouring world.”

A pair of studies were published in the Science Advances journal.