Alien Life? Astronomers Predict Contact by 2025

Earthlings could make contact with extraterrestrial beings by the year 2025, two astronomers predict in a new book. The authors say it's unlikely space aliens look like Hollywood's ET—little, green, and hairless—and that while aliens are highly unlikely to pay Earth a visit, they may be sending radio signals across space to let us know they exist.

The book, Cosmic Company, "is an explication of why we think they're out there, how we're looking for them, what they must be like, and a little bit of what it might mean" to find life on other planets, said co-author Seth Shostak, a senior astronomer at the Search for Extraterrestrial Intelligence Institute (SETI) in Mountain View, California.

Beyond Our Galaxy

Shostak and co-author Alexandra Barnett, an astronomer and executive director of the Chabot Space and Science Center in Oakland, California, base their predictions on a number of factors.

They include the billions of years in which extraterrestrial life could have evolved and the abundance of planets and stars elsewhere in the universe that are likely to mimic environmental conditions found on Earth.

"It's a matter of statistics, really," said Barnett. "Depending on who you talk to, the universe is 12 to 15 billion years old. Humans have only been around for 40,000 years. We really are the new kids on the block. It would just be too tough a pill to swallow to believe that nothing else has evolved in all that time and space."

The universe is indeed vast. In 1924 astronomer Edwin Hubble showed that there are galaxies beyond our own. "More than a half century later, the Hubble telescope has shown that there are at least 100 billion such galaxies," said Shostak. Our galaxy, the Milky Way, is home to at least 100 billion stars.

Planets are also plentiful. Since 1995, when the first Jupiter-sized planet outside of our solar system was found, astronomers have been able to identify about 100 more planets, all of them around 300 times more massive than Earth.

"Planets really are as common as phone poles," said Shostak. "Right now, we know that there are planets out there [orbiting] ten or twenty percent of the stars we look at. So far, only huge planets have been found, but it would be a big surprise if there were only big ones. I don't think anyone expects that to be the case."

But in 2007, NASA will launch the Kepler Mission, a satellite probe able to detect smaller planets the size of Mercury, Mars, or the Earth. The mission is specifically designed to look for planets in what scientists consider the habitable zone: the distance from a star where liquid water can exist on the planet's surface.