A research paper, in the journal Icarus, claimed that hydrogen gas flowing throughout the planet’s atmosphere disappeared at the surface. This suggested that alien forms could in fact breathe.

A second paper, in the Journal of Geophysical Research, concluded that there was lack of the chemical on the surface Scientists were then led to believe it had been possibly consumed by life.

Researchers had expected sunlight interacting with chemicals in the atmosphere to produce acetylene gas. But the Cassini probe did not detect any such gas.

In 2008, astronomers found organic chemicals on a planet outside our solar system, which was also heralded as a milestone in the hunt for extraterrestrial life.

Researchers identified water in the atmosphere of HD 189733b, a so-called alien planet close to its parent star and too hot for conditions favourable for life as we understand it.

But the ability of scientists to analyse its atmosphere and detect carbon-based molecules was a crucial feat in efforts to find planets that may harbour extraterrestrial life.

The finding, reported in the journal Nature, made the planet one of the best understood of hundreds detected. It was discovered in 2005 in the constellation Vulpecula, a realm so distant that it takes light 63 years to reach Earth.

The achievement demonstrated the ability to detect organic molecules in "Goldilocks zones'' – so-called because they are just right for liquid water, neither too hot nor too cold.

The planet is made of gas similar, but hotter, to that found on Jupiter. Previous studies predicted that methane and water would be present in its atmosphere, but definitive evidence had not been found. Water has already been detected on another alien world.

Using light analysed by the Hubble Space Telescope, Dr Mark Swain of the Jet Propulsion Laboratory and the California Institute of Technology, Pasadena, and colleagues confirmed the presence of methane. They also reported that they found the signature of water, though carbon monoxide, originally expected to be abundant in the upper atmosphere, was not identifiable.

On Earth, methane is produced by natural sources such as termites, oceans and cows, but also man-made sources such as waste landfills.

A discovery much closer to home also ignited a frenzy of speculation about aliens last year, when experts detected a microbe at the bottom of a lake capable of living in conditions previously thought to be inhospitable to any form of life.

Researchers found a microbe at the bottom of Mono Lake in Yosemite National Park that was thriving in an arsenic—rich environment previously thought too poisonous for any form of life to survive.

It raised the prospect that similar life could exist on planets without the Earth's benevolent atmosphere.

A research paper, in the journal Icarus, claimed that hydrogen gas flowing throughout the planet’s atmosphere disappeared at the surface. This suggested that alien forms could in fact breathe.

A second paper, in the Journal of Geophysical Research, concluded that there was lack of the chemical on the surface Scientists were then led to believe it had been possibly consumed by life.

Researchers had expected sunlight interacting with chemicals in the atmosphere to produce acetylene gas. But the Cassini probe did not detect any such gas.

In 2008, astronomers found organic chemicals on a planet outside our solar system, which was also heralded as a milestone in the hunt for extraterrestrial life.

Researchers identified water in the atmosphere of HD 189733b, a so-called alien planet close to its parent star and too hot for conditions favourable for life as we understand it.

But the ability of scientists to analyse its atmosphere and detect carbon-based molecules was a crucial feat in efforts to find planets that may harbour extraterrestrial life.

The finding, reported in the journal Nature, made the planet one of the best understood of hundreds detected. It was discovered in 2005 in the constellation Vulpecula, a realm so distant that it takes light 63 years to reach Earth.

The achievement demonstrated the ability to detect organic molecules in "Goldilocks zones ' ' – so-called because they are just right for liquid water, neither too hot nor too cold.

The planet is made of gas similar, but hotter, to that found on Jupiter. Previous studies predicted that methane and water would be present in its atmosphere, but definitive evidence had not been found. Water has already been detected on another alien world.

Using light analysed by the Hubble Space Telescope, Dr Mark Swain of the Jet Propulsion Laboratory and the California Institute of Technology, Pasadena, and colleagues confirmed the presence of methane. They also reported that they found the signature of water, though carbon monoxide, originally expected to be abundant in the upper atmosphere, was not identifiable.

On Earth, methane is produced by natural sources such as termites, oceans and cows, but also man-made sources such as waste landfills.

A discovery much closer to home also ignited a frenzy of speculation about aliens last year, when experts detected a microbe at the bottom of a lake capable of living in conditions previously thought to be inhospitable to any form of life.

Researchers found a microbe at the bottom of Mono Lake in Yosemite National Park that was thriving in an arsenic—rich environment previously thought too poisonous for any form of life to survive.

It raised the prospect that similar life could exist on planets without the Earth 's benevolent atmosphere.