Nasa scientists say the gas emissions could have either a geological or biological source - as The Sun exclusively revealed today.
Nasa tonight streamed it historic findings live on its online television channel which you can watch by clicking HERE
Life is responsible for more than 90 per cent of the Earth’s atmospheric methane.
Experts believe there is a good chance that organisms produced the gas emissions - as large as some of those seen on Earth - on Mars too.
Scientist Michael Mumma of NASA’s Goddard Space Flight Center said: “This raises the probability substantially that life was there or still survives at the present.
“We think the probability is much higher now based on this evidence.”
The bugs that made it may have vanished millions of years ago, leaving the methane frozen under the planet’s surface.
But another possibility is that some hardy organisms still survive on the Red Planet, living underground without sunlight and using hydrogen from water for energy. Similar microbes exist on Earth.
Methane produced by the action of water on hot carbon bearing rocks, as occurs in volcanic regions on Earth, is the alternative explanation.
Whatever the source is, scientists agree that something is replenishing the methane.
The find is seen as exciting new evidence that Martian microbes are still alive today.
Some scientists reckon methane is also produced by volcanic processes. But there are NO
known active volcanoes on Mars.
Furthermore, Nasa has found the gas in the same regions as clouds of water vapour, the vital “drink” needed to support life.
Experts speculate that the methane is being emitted as a waste product by organisms called methanogens living in water beneath underground ice.
And they would have to be alive today because the methane would otherwise have been lost from the Martian atmosphere.
John Murray — a member of the Mars Express European space probe team — believes the mini-Martians may be in a form of suspended animation and could even be REVIVED
He has found overwhelming evidence of a vast frozen ocean beneath the dust near the Martian equator where simple life could have thrived as microbes.
Today’s briefing will feature a star panel of Mars experts headed by Michael Meyer, chief scientist for Nasa’s Mars programme.
UK Mars expert Professor Colin Pillinger believes the methane can only point to the presence of life on the planet.
His ill-fated Beagle 2 probe was carrying a laboratory that would have looked directly for such signs of life when it crashed on Christmas Day 2003.
Prof Pillinger told The Sun last night: “Methane is a product of biology. For methane to be in Mars’ atmosphere, there has to be a replenishable source.
“The most obvious source of methane is organisms. So if you find methane in an atmosphere, you can suspect there is life.
“It’s not proof, but it makes it worth a much closer look.”
Nasa’s findings confirm studies by Europe’s Mars Express probe, which has been orbiting the planet for five years and also reported signs of methane in 2004.
Britain’s top space expert Nick Pope last night hailed the new evidence of life as “the most important discovery of all time”.
He said: “What could be more profound than to know it’s not just us out there?
We’ve really only scratched the surface — it’s an absolute certainty that there is life out there and we are not alone.
“If there is life on Mars then the logical conclusion is that there must be life elsewhere too.
“If it’s happened here on Earth, then why shouldn’t it happen anywhere? The implication is this is a universal law.
“Mars is very similar to Earth. It’s about the same size, it’s a rocky inner planet.
“Most scientists believe it probably has liquid water which is almost universally agreed as the pre-requisite for life. I am certain there is other life in the Universe and, most likely, intelligent life.”
The Red Planet has gripped the public imagination for more than a century as a possible home for aliens.
But life could not survive on its surface because, unlike the Earth, Mars has no magnetic shield to protect it against deadly sun radiation.
The planet resembles our own in many ways. It is made of rock, it has an atmosphere and weather systems.
Although much smaller with a diameter of around 4,222 miles, Mars’ day is just 40 minutes longer than ours and its tilted axis gives it seasons.
Water has been found in the form of buried ice and scientists believe that two billion years ago, Mars was covered with liquid oceans.
Proof that water is still on Mars came in 2007 when Mars Express used ground-piercing radar to study the region around the planet’s South Pole.
Nasa’s latest lander Phoenix dug up chunks of Martian ice last year. It swiftly evaporated into the thin atmosphere.
Nasa have controversially hit the headlines before for claiming evidence for Martians.
In 1996, they said they had discovered fossilised organisms in a meteorite from the planet.
But other scientists were sceptical.