Washington, Sep 12 (IANS): NASA scientists have successfully simulated the atmosphere of alien worlds in the lab, yielding positive results for astronomers searching for life beyond earth.

"When we ran these experiments, we found that in some cases there was a significant amount of ozone that built up in the atmosphere, despite there not being any oxygen flowing into the atmosphere," explained Shawn Domagal-Goldman from NASA's Goddard Space Flight Center in Greenbelt, Maryland, the US.

This has important implications for our future plans to look for life beyond Earth, he added.

The research strengthens the argument that methane and oxygen together, or methane and ozone together, are still strong signatures of life.

Methane and oxygen molecules together are a reliable sign of biological activity because methane does not last long in an atmosphere containing oxygen-bearing molecules.

"If both are seen together in an atmosphere, the methane was freshly delivered because the oxygen will be part of a network of reactions that will consume the methane. You know the methane is being replenished. The best way to replenish methane in the presence of oxygen is with life," explained co-author Antigona Segura from the Universidad Nacional Autonoma de Mexico in Mexico City.

The opposite is true, as well.

"In order to keep the oxygen around in an atmosphere that has a lot of methane, you have to replenish the oxygen, and the best way to do that is with life," Segura noted.

The team now plans to use this research -- done at the NASA Astrobiology Institute's Virtual Planetary Laboratory -- to make recommendations about the requirements for future space telescopes designed to search exoplanet atmospheres for signs of alien life.

The paper appeared in the Astrophysical Journal.