Astronomers say they are on the verge of finding planets like Earth orbiting other stars, a key step in determining if alien life-forms exist.
A top Nasa astronomer and other leading scientists say that within four or five years they should discover the first Earth-like planet where life could develop, or may have already.
A planet close to the size of Earth could even be found this year if preliminary hints from a new space telescope pan out.
At the annual American Astronomical Society conference in Washington this week, each discovery involving so-called "exoplanets" - those outside our solar system - pointed to the same conclusion: quiet planets like Earth where life could develop are probably plentiful, despite a violent universe of exploding stars, crushing black holes and colliding galaxies.
Nasa's new Kepler telescope and a wealth of new research from the suddenly hot and competitive exoplanet field generated noticeable buzz at the convention.
Scientists are talking about being at "an incredible special place in history" and closer to answering a question that has dogged humanity since the beginning of civilisation.
"The fundamental question is: are we alone? For the first time, there's an optimism that sometime in our lifetimes we're going to get to the bottom of that," said Simon "Pete" Worden, an astronomer who heads Nasa's Ames Research Centre.
"If I were a betting man, which I am, I would bet we're not alone - there is a lot of life."
Even the Roman Catholic Church has held scientific conferences about the prospect of extraterrestrial life, including a meeting last November.
"These are big questions that reflect upon the meaning of the human race in the universe," director of the Vatican Observatory, the Rev Jose Funes, said in an interview at this week's conference.
Mr Worden said: "I would certainly expect in the next four or five years we'd have an Earth-sized planet in the habitable zone."
His centre runs the Kepler telescope, which is making an intense planetary census of a small portion of the galaxy.
Unlike the Hubble Space Telescope, which is a general instrument, Kepler is a specialised telescope just for planet-hunting.
Its sole instrument is a light meter that measures the brightness of more than 100,000 stars simultaneously, watching for anything that causes a star to dim. That dimming is often a planet passing in front of the star.
Any planet that could support life would almost certainly need to be rocky rather than gaseous and in just the right location. Planets that are too close to their star will be too hot, and those too far away are too cold.
"Every single rock we turn over, we find a planet," said Ohio State University astronomer Scott Gaudi. "They occur in all sorts of environments, all sorts of places."
Researchers are finding exoplanets at a dizzying pace. In the 1990s, astronomers found a couple of new planets a year. For most of the last decade, it was up to a couple of planets every month.
This year, planets are being found on about a daily basis, thanks to the Kepler telescope. The number of discovered exoplanets is now well past 400.
None of those has the right components for life, but that is about to change, say experts.
"From Kepler, we have strong indications of smaller planets in large numbers, but they aren't verified yet," said Geoff Marcy of the University of California at Berkeley, one of the founding fathers of the field of planet-hunting and a Kepler scientist.
But there is a big caveat. Most of the early exoplanet candidates found by Kepler are turning out to be something other than a planet, such as another star crossing the telescope's point of view, when double and triple-checked, says top Kepler scientist Bill Borucki.
Kepler is concentrating on about one-four hundredth of the night-time sky, scanning more than 100,000 stars, ranging from a few hundred to a few thousand light years away.
A light year is about 5.9 trillion miles. So such planets are too far to travel to, and they cannot be viewed directly like the planets in our solar system.
If there were an Earth-like body in the area Kepler is searching, the telescope would find it, Mr Marcy said. But it can take three years to confirm a planet's orbital path.
Mr Marcy, who this week announced finding a planet just four times larger than Earth, said he did not like to speculate how many stars had Earth-like planets, but said: "Seventy per cent of all stars have rocky planets.
"If you are in the kitchen and are trying to cook up a habitable planet, we already know that in the cosmos, all the ingredients are there."