A powerful orbital telescope launched in March with a mission to look for habitable counterparts to Earth should also be able to detect small moons that could nurture life, scientists said Thursday.

The NASA spacecraft Kepler is designed to monitor more than 100,000 stars over the next three years, looking for telltale dips in their brightness as orbiting planets pass in front of them.

These so-called transit events can yield tantalising details about exoplanets, as planets beyond our Solar System are known.

So far, 358 exoplanets have been spotted since the first was found in 1995.

Frustratingly, none is comparable to Earth.

Our planet sits in the "Goldilocks zone" where the temperature is not too hot for our atmosphere to be stripped away nor too cold for our seas to freeze -- but just right to have liquid water, the stuff of life.

Most of the finds have been gas giants, similar to Jupiter, rather than solid ones like Earth, and they orbit their stars at scorchingly close distances.

Kepler, according to the new study, should have the power to find even Earth-like satellites of exoplanets.

A team led by David Kipping of University College London modelled the properties of the instruments aboard Kepler and compared this with the expected signal strength that a habitable "exomoon" would generate.

They found that habitable exomoons down to just a fifth of the mass of Earth could be spotted.

No exomoon has been found yet, but this could change with the advances provided by Kepler, they believe.

"For the first time, we have demonstrated that potentially habitable moons up to hundreds of light years away may be detected with current instrumentation," said Kipping.

"It seems probable that many thousands, possibly millions, of habitable exomoons exist in the Galaxy and now we can start to look for them."

Even if an Earth-like exoplanet or exomoon is found, we have no chance of getting there with our puny chemical-powered spaceships.

Discovering such a place, though, would add a big piece to the puzzle as to whether life has the potential to exist elsewhere in the Universe.

The paper appears in the journal Monthly Notices, published by Britain's Royal Astronomical Society.