Life on Mars? The Red Planet's atmosphere once contained MORE oxygen than Earth until it was damaged in a catastrophic collision with another world the size of Pluto

Craft: This shows a self-portrait taken by the NASA rover Curiosity in Gale Crater on Mars. Measurements of the Martian air by the rover found it is mostly made of carbon dioxide with traces of other gases

Theory: There was interest in what may have existed in the past on Mars, after Curiosity found that much of the planet's atmosphere has been lost over time, suggesting it was once warmer

A team of Nasa scientists claim that a change in the ratio of two different kinds of argon gas is evidence that the atmosphere has been stripped away.

Nasa's Dr Chris Webster said: 'As Mars became a planet and its magma ocean solidified, catastrophic outgassing occurred while volatiles were delivered by impact of comets and other smaller bodies.

'Solar wind, and the possible impact by a Pluto-sized body is thought to have stripped much of the initial early atmosphere from the planet, and since then the atmosphere has developed as a balance between volcanic injection and loss to space.'

The Nasa scientists were investigating the atmosphere after one of their telescopes on Earth had detected a surprising and mysterious amount of methane in three regions in the Martian western hemisphere.

This presence of methane could have suggested there was some form of life living on the planet.

Yet the Curiosity rover did not find any methane, which has disappointed those who believe microbes may still linger there.

On Earth, methane is mainly a by-product of life - from animal digestion and decaying plants - and the gas can also be produced by non-biological processes. 

Disappointment: Last year, the Curiosity team reported no definitive whiff of methane near the landing site, and since then, the rover has taken several more air samples

Red planet: A view of Mars that was stitched together by images taken by NASA's Viking Orbiter spacecraft

But last year, the Curiosity team reported no definitive whiff of methane near the landing site, and since then, the rover has taken several more air samples.

There are also plans to sniff the atmosphere during a drive to the Mount Sharp mountain. And in the autumn NASA is set to launch a Mars-orbiting spacecraft aimed at solving the methane mystery.

Called Maven, the craft will target the Martian atmosphere. Scientists want to know if it actually exists, determine the abundance and whether that varies by year or location.

'The fact that it’s turned out to be pretty much disproven - it’s not a surprise, but a disappointment perhaps,' planetary scientist Adrian Brown of the SETI Institute in California, told Wired magazine.

The Curiosity found the air is made mostly of carbon dioxide. This closely matched what the twin Viking landers detected in the late 1970s and what scientists have gleaned from Martian meteorites.

And there was also interest in what may have existed in the past on Mars, after Curiosity found that much of the planet’s atmosphere has been lost over time, suggesting it was once warmer.

This would have been more conducive to liquid water flowing on the surface - and potentially even life existing on the planet, reported Wired.

Mars' atmosphere is overwhelmingly dominated by carbon dioxide, unlike Earth's air, which is a mix of nitrogen and oxygen. However, there was still a small surprise.

Results: The nuclear-powered, six-wheel rover set down in an ancient crater near the Martian equator almost a year ago