In the search for extraterrestrial intelligence, some have been accused of harboring a sense of “carbon chauvinism,” expecting other life-forms in the universe to be made of the same biochemical building blocks as we are and tailoring our searches accordingly. Here are 10 examples of biological and nonbiological systems that stretch the definition of “life.”

Funded by Russian billionaire Yuri Millner, the initiative will give the search for intelligent life a major boost.

Russian billionaire Yuri Milner announces most comprehensive hunt for alien life.

A new $100 million, 10-year search for intelligent life in the universe was announced today (July 20) by famed scientist Stephen Hawking and other prominent researchers.

Alien life forms might be living right under our noses, but how can we find them if we don’t know what we’re looking for?

A sensational claim that ESA’s Philae spacecraft has landed on a comet teeming with life doesn’t hold water.

In the constellation Boötes, a star a bit smaller than our sun flares sporadically, dimming and brightening, but still too faint to be seen with the naked eye. Scientists have named this red dwarf Gliese 526 and categorized it as a star that just might have a habitable planet or two. No one has spotted a planet yet, but the abundance of planets orbiting other, similar stars make the chances look good. If life exists in that star system, we would be neighbors...

New photos revealed at a recent event in Mexico have been said to depict the body of an extraterrestrial alien recovered from the Roswell UFO crash of 1947.

If aliens landed in Central Park tomorrow, how would humankind respond? Would we point every tank and gun squarely on the spacecraft? Or would we offer a more neighborly greeting? What questions would we ask these extraterrestrials? And what would we tell them about us?

Scientists at a US science conference have said it is now time to actively try to contact intelligent life on other worlds.

Are we the only island of life in the vastness of space, or is our Galaxy teeming with other civilisations? We've long been intrigued by the idea that we are not alone. The search for extra-terrestrial intelligence (SETI) - was born from this curiosity - the use of sophisticated scientific methods to try to detect a signal coming from life elsewhere in the Galaxy. In the 1960s, radio astronomy was put to work in the search. Radio telescopes surveyed the sky...

We have yet to discover any signs of aliens, a troubling observation that has led to much speculation. One possible solution to the Great Silence is that nobody's out there. It's a conclusion that sounds impossible to believe, but there may be something to it. Here's why we may be alone in the universe.

The space agency is out with some new tips for going about your search the right way and avoiding the trap of false positives. Researchers at NASA's Astrobiology Institute’s Virtual Planetary Laboratory conducted thousands of simulations of various atmospheres and star types over the course of four years and came up with a few new recommendations.

Alien hunter extraordinaire Jill Tarter, the inspiration for the movie Contact, speaks about her quest to detect signs of intelligent life.

Sigourney Weaver’s Ripley stands in front of the squad of ten cocky, poised space marines. They laugh and joke, oozing bravado and testosterone—even the women. As the shavetail lieutenant lays out the situation, Bill Paxton’s mouthy PFC Hudson interrupts: "Is this going to be a stand-up fight, sir, or another bug hunt?" "All we know is that there’s still no contact with the colony," replies the lieutenant, Gorman, "and that a xenomorph may be involved."

NASA predicts that 100 million worlds in our own Milky Way galaxy may host alien life, and space program scientists estimate that humans will be able to find life within two decades.

Neil DeGrasse Tyson tells MSNBC that it's possible aliens have visited and already concluded that there is no intelligent life on Earth.

Two top astronomers told Congress today that it would be "bizarre if we are alone" and asked for continued funding to detect extraterrestrial life. Dan Werthimer, director of the SETI Research Center at the University of California, Berkeley (SETI is short of "Search for Extraterrestrial Intelligence") also told the House Committee on Science, Space and Technology that he thinks the possibility of microbial life on other planets is close to 100 percent.

Whether you're a die hard aliens-are-real-and-they-want-to-kill-us-all conspiracy theorist or you think that the closest we'll ever get to meeting extra terrestrials is shaking hands with Dennis Rodman, in the most objective sense possible these are 25 of the most famous UFO sightings on record.

Humans are not yet ready to make contact with intelligent aliens, a study suggests. Space psychologist Professor Gabriel de la Torre came to the conclusion after questioning 116 American, Italian and Spanish university students. The survey assessed participants' knowledge of astronomy and their perception of cosmological order - the "place" things occupy in the universe.