An alien spacecraft hovers towards Manhattan in a scene from the 1996 blockbuster film "Independence Day". [ Photo and caption accompanied original article]
Rapid technological leaps forward in the last 10 years mean mankind is closer than ever before to knowing whether extra-terrestrial life exists in our galaxy, one of Britain's leading scientists said on Tuesday.

Astronomer and President of the Royal Society (academy of science) Martin Rees said science had made enormous progress in the search for planets grouped around other distant stars -- a discipline he stressed did not exist in the 1990s.

"Now we know that most of the stars, like the sun, are likely to have planetary systems around them and we have every reason to suspect that many of them have planets that are rather like our earth," Rees told Reuters in an interview.

He said great strides in space search techniques over the last decade had removed one of the big obstacles in finding other worlds, and possibly even complex life forms, in our Milky Way galaxy of 100 million stars.

"Indeed, we live in very exciting times," he said.

And judging by the 250 eminent scientific minds who have gathered in London to attend a Royal Society conference on the "The detection of extra-terrestrial life," he is not the only enthusiast.

The meeting, which ends on Tuesday, is the first in the Royal Society's 350-year history to discuss alien life forms.

Hugely significant projects like the launch last spring of NASA's Kepler spacecraft, a space observatory designed to find earth-like planets in the cosmos, as well as the use of more advanced satellites have brought us closer to solving one of the universe's greatest mysteries, Rees said.

"Kepler is the first one capable of detecting substantial numbers of planets no bigger than the earth. So we will know within two or three years which are earth-like and in earth-like orbits in the sense of being the right distance from their parent star."

Rees, who is professor of cosmology and astrophysics at Cambridge University and holds the honorary title of Astronomer Royal, also believes mankind is on the cusp of unlocking one of life's greatest mysteries.

"I'm certainly pretty confident biologists will understand the origin of life on earth this century. I suspect in 20 years we will have much clearer ideas of how life began," he said.

"And that is going to be very important to answering how likely it is to have started elsewhere and where to look."

He added: "If we understood how life began on earth, that would give us a clue to how likely it was to originate elsewhere and what the optimum environments were."

Those expecting the exotic aliens of sci-fi films should extra-terrestrials be discovered will be disappointed, however.

Many top minds say extra-terrestrial life may be totally beyond our sensory abilities and comprehension.

"Even those who believe complex life is widespread, aren't especially optimistic about current searches getting positive results," Rees said.

"There may be advanced life of a kind we can't conceive, a kind that doesn't reveal itself by electromagnetic radiation -- a kind that isn't communicating at all."