WHAT'S the most obvious sign of life on another planet? Believe it or not, it's flatulence.

In a new spin on a "whoopee" moment, scientists believe such "gas byproducts" will be the first clues to existence around distant stars.

In particular they want to sniff out methane, an animal byproduct on the nose here on Earth because of its greenhouse gas properties.

But methane is not the only life-related gas scientists are seeking that is wafting among the stars.

Photosynthesis among plants emits oxygen. Microbes produce nitrous oxide. Seaweeds let-off chloromethane.

All these chemicals, when detected in an atmosphere in sufficient quantities, will give astronomers the first real whiff of alien life.

A team of scientists has told the European Planetary Science Congress of this plan to sense life beyond our solar system.

"For the first time we are reaching a point where serious scientific debate can be

applied to address the age-old question: are we alone?" Lee Grenfell of the DLR In­sti­tute of Plan­e­tary Re­search in Ber­lin said.

The chemicals in an atmosphere distort light passing through it in predictable patterns. These "fingerprints" can then be extracted from the spectrum of light reflected by the planet towards Earth.

It will take a new generation of telescopes capable of peering across the vastness of space with fine enough detail to extract these distinct "biomarkers" from a planet's atmosphere - but Mr Grenfell points out such telescopes are already on the way.

The European Extremely Large Telescope is likely to be one of the first capable of capturing such clues to enter service.

TITLE: Next Generation Telescopes

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CAPTION: Next Generation Telescopes To Solve the Biggest Mysteries of the Universe

"We've developed computer models of exoplanets which simulate the abundances of different biomarkers and the way they affect the light shining through a planet's atmosphere," Mr Grenfell said.

"In our simulations, we modelled an exoplanet similar to the Earth, which we then placed in different orbits around stars, calculating how the biomarker signals respond to differing conditions," he explained.

"We focused on red-dwarf stars, which are smaller and fainter than our Sun, since we expect any biomarker signals from planets orbiting such stars to be easier to detect."

Such a technique does have its limitations.

It assumes that life out there is the same as down here - something nobody is certain about.

And all of these biomarkers can be produced via non-living processes, making verification a difficult process.

It's life Jim, but not necessarily as we know it.