Video: The odds of alien life

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updated 12/8/2010 11:14:22 AM ET 2010-12-08T16:14:22

Lately, a handful of new discoveries make it seem more likely that we are not alone — that there is life somewhere else in the universe.

In the past several days, scientists have reported there are three times as many stars as they previously thought. Another group of researchers discovered a microbe can live on arsenic, expanding our understanding of how life can thrive under the harshest environments. And earlier this year, astronomers for the first time said they'd found a potentially habitable planet.

"The evidence is just getting stronger and stronger," said Carl Pilcher, director of NASA's Astrobiology Institute, which studies the origins, evolution and possibilities of life in the universe. "I think anybody looking at this evidence is going to say, 'There's got to be life out there.'"

A caveat: Since much of this research is new, scientists are still debating how solid the conclusions are.

Another reason to not get too excited is that the search for life starts small — microscopically small — and then looks to evolution for more. The first signs of life elsewhere are more likely to be closer to slime mold than to E.T. It can evolve from there.

Some science, some pure guesswork
Scientists have an equation that calculates the odds of civilized life on another planet. But much of it includes factors that are pure guesswork on less-than-astronomical factors, such as the likelihood of the evolution of intelligence and how long civilizations last. Stripped to its simplistic core — with the requirement for intelligence and civilization removed — the calculations hinge on two basic factors: How many places out there can support life? And how hard is it for life to take root?

Story: Figure the odds of finding E.T.

What last week's findings did was both increase the number of potential homes for life and broaden the definition of what life is. That means the probability for alien life is higher than ever before, agree 10 scientists interviewed by The Associated Press.

Seth Shostak, senior astronomer at the SETI Institute in California, ticks off the astronomical findings about planet abundance and Earthbound discoveries about life's hardiness. "All of these have gone in the direction of encouraging life out there and they didn't have to."

Scientists who looked for life were once dismissed as working on the fringes of science. Now, Shostak said, it's the other way around. He said that given the mounting evidence, to believe now that Earth is the only place harboring life is essentially like believing in miracles. "And astronomers tend not to believe in miracles."

Astronomers, however, do believe in proof. They don't have proof of life yet. There's no green alien or even a bacterium that scientists can point to and say it's alive and alien. Even that arsenic-munching microbe discovered in Mono Lake in California isn't truly alien. It was manipulated in the lab.

But, says NASA astrobiologist Chris McKay, who has worked on searches for life on Mars and extreme places on Earth, "There are real things we can point to and show that being optimistic about life elsewhere is not silly."

Where such life might exist
First, there's the basic question of where such life might exist. Until a few years ago, astronomers thought life was only likely to be found on or around planets circling stars like our sun. So that's where the search of life focused — on stars like ours.

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That left out the universe's most common stars: red dwarfs, which are smaller than our sun and dimmer. Up to 90 percent of the stars in the universe are red dwarf stars. And astronomers assumed planets circling them would be devoid of life.

But three years ago, NASA got the top experts in the field together. They crunched numbers and realized that life could exist on planets orbiting red dwarfs. The planets would have to be closer to their star and wouldn't rotate as quickly as Earth. The scientists considered habitability and found conditions near these small stars wouldn't be similar to Earth but would still be acceptable for life.

That didn't just open up billions of new worlds, but many, many times that.

Last week, a Yale University astronomer said he estimates there are 300 sextillion stars — triple the previous number. Lisa Kaltenegger of Harvard University says scientists now believe that as many as half the stars in our galaxy have planets that are two to 10 times the size of Earth — "super Earths" which might sustain life.

Then the question is how many of those are in the so-called Goldilocks zone — not too hot, not too cold. The discovery of such a planet was announced in April, although some scientists are challenging that.

The other half of the equation is: How likely is life? Over the past decade and a half, scientists have found Earth life growing in acid, in Antarctica and other extreme environments. But nothing topped last week's news of a lake bacterium that scientists could train to thrive on arsenic instead of phosphorous. Six major elements have long been considered essential for life — carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. This changed that definition of life.

By making life more likely in extreme places, it increases the number of planets that are potential homes for life, said Kaltenegger, who also works at the Max Planck Institute in Germany.

Donald Brownlee, an astronomer at the University of Washington, is less optimistic because he believes what's likely to be out there is not going to be easy to find — or that meaningful. If it's out there, he said, it's likely microbes that can't be seen easily from great distances. Also, the different geologic and atmospheric forces on planets may keep life from evolving into something complex or intelligent, he said.

Mars most likely candidate
If life is going to be found, Mars is the most likely candidate. And any life is probably underground where there is water, astronomers say. Other possibilities include Jupiter's moon Europa and Saturn's moons Enceladus and Titan.

There's also a chance that a telescope could spot a planet with an atmosphere that suggests photosynthesis is occurring, Kaltenegger said. And then there's the possibility of finding alien life on Earth, perhaps in a meteorite, or something with an entirely different set of DNA.

And finally, advanced aliens could find us or we could hear their radio transmissions, McKay said. That's what the SETI Institute is about, listening for intelligent life.

That's where Shostak puts his money behind his optimism. At his public lectures, Shostak bets a cup of coffee for everyone in the audience that scientists will find proof of alien life by about 2026. The odds, he figures, have never been more in his favor.

Copyright 2010 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

Explainer: SETI: 50 years of searching for E.T.

  • Somewhere out there, alien civilizations might be communicating with each other. They might even be trying to contact us. In 1960, this reasoning compelled astronomer Frank Drake to point a radio telescope at the stars and listen for chatter. He didn't hear E.T. calling us, calling home, or calling anywhere else during his four-month-long experiment at the National Radio Astronomy Observatory in Green Bank, W.Va., but the effort officially kicked off what is known as SETI, the search for extraterrestrial intelligence. Click the "Next" label to check out highlights from the first 50 years of the search.

    — By John Roach, msnbc.com contributor

  • 1974: Earthlings send message to aliens

    By 1974, Drake and his colleagues still hadn't heard anything from ET, but they hadn't given up hope. Instead, they sent a message out to the aliens with the Arecibo radio telescope in Puerto Rico, the first deliberate message sent from Earth out to the stars. The message contained information about life-giving chemicals, DNA, a simple drawing of our solar system, and pictures of human beings and the Arecibo telescope. The string of 1's and 0's was sent to a group of about 300,000 stars in called the Great Cluster in Hercules, Messier 13, about 25,000 light years away.

  • 1977: The Wow Signal

    Courtesy of Jerry Ehman / Bigear

    Did E.T. make a prank call to Earth on Aug. 15, 1977? We may never know for sure, but astronomer Jerry Ehman was struck enough by a string of letters and numbers on a printout of radio data from the Big Ear Radio Observatory at Ohio State University to scribble "Wow!" in the margin. The extraordinary signal might have been E.T., or something else. Whatever it was, astronomers have been unable to find it again despite dozens of searches, leaving open the possibility that E.T. called but hung up after the first ring.

  • 1992-1993: NASA's brief search

    U.S. Senate Historical Office

    Exactly 500 years after Christopher Columbus arrived in the New World, NASA officially launched its SETI program, the High Resolution Microwave Survey. Experts called it the most ambitious and technologically advanced alien-search effort ever conducted, but after just a year of operation the program was squashed. Sen. Richard Bryan, D-Nev., shown here, led the effort to kill the program, telling the Senate that "millions have been spent and we have yet to bag a single little green fellow. Not a single Martian has said take me to your leader, and not a single flying saucer has applied for FAA approval."

  • 1995: Project Phoenix rises from ashes

    Image: Paraffin candles
    Seth Shostak / SETI Institute

    When NASA funding for alien searches ran dry, private enterprise picked up the pieces - including some of NASA's equipment - and launched Project Phoenix. The targeted search focused on about 1,000 stars thought most likely to harbor alien civilizations and was conducted at various radio astronomy observatories around the world. In this image, SETI Institute astronomer Seth Shostak looks for E.T.'s call on a computer bank at the Arecibo observatory in Puerto Rico.

  • 1999: SETI for the masses

    SETI @ Home / UC-Berkeley
    Five million Internet users have contributed more than 3 million years of processing time to the search for signals from extraterrestrial civilizations through the SETI @ Home screensaver program, shown here.

    Hundreds, then thousands, and ultimately millions of computer users around the world got in on the search for E.T. with the 1999 launch of SETI@home, a distributed computing project run at the University of California at Berkeley. The program enlists personal computers to sort through the mountains of SETI data, one chunk at a time, collected by the Arecibo radio telescope. The combined power of all the computers running the program essentially acts like a super duper supercomputer, but at a fraction of the cost.

  • 2007: Telescope array turned on

    For most of the past 50 years, SETI projects have required astronomers to wait in line for time on giant radio telescopes around the world. That changed in 2007 with the opening of the Allen Telescope Array, a constellation of 42 radio telescopes with 20-foot-wide dishes in the scrublands about 300 miles northeast of San Francisco. The array, privately financed by software billionaire Paul Allen and others, puts the search for E.T. front and center. The project is jointly run by the SETI Institute and the University of California at Berkley. In the coming decades the array may grow to 350 antennas, making it one of the most powerful radio telescopes in the world.

  • The future of SETI

    NASA
    An artist's interpretation of the Kepler observatory in space. Credit: NASA

    As of this writing, extraterrestrials remain elusive, assuming that they exist at all. Given that the search is only 50 years old, many astronomers see little reason to despair - things are just getting going. NASA recently lent a new hand to the search with its Kepler mission, a space telescope that is looking for Earthlike, habitable planets around thousands of stars in our Milky Way galaxy. Detection of these planets will help SETI scientists focus their efforts.

    Other ideas include a push to expand the search beyond just radio signals. Paul Davies, a physicist at Arizona State University and author of several popular science books, argues that messages from E.T. might even be floating around in the junk DNA of terrestrial organisms and that we should start searching decoded genomes for the biotech equivalent of a message in a bottle.

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