西安普惠体检中心北郊:Alien Life, Coming Slowly Into View - NYTimes.com

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Op-Ed Contributor

Alien Life, Coming Slowly Into View

Toronto
Paul Sahre

I REMEMBER the first time the concept of another world entered my mind.It was during a walk with my father in our garden in Sri Lanka. Hepointed to the Moon and told me that people had walked on it. I wasastonished: Suddenly that bright light became a place that one couldvisit.

Schoolchildren may feel a similar sense of wonder when they see picturesof a Martian landscape or Saturn’s rings. And soon their views of alienworlds may not be confined to the planets in our own solar system.

After millenniums of musings and a century of failed attempts, astronomers first detected an exoplanet,a planet orbiting a normal star other than the Sun, in 1995. Now theyare finding hundreds of such worlds each year. Last month, NASAannounced that 1,235 new possible planetshad been observed by Kepler, a telescope on a space satellite. Six ofthe planets that Kepler found circle one star, and the orbits of five ofthem would fit within that of Mercury, the closest planet to our Sun.

By timing the passages of these five planets across their sun’s visage —which provides confirmation of their planetary nature — we can witnesstheir graceful dance with one another, choreographed by gravity. Thesediscoveries remind us that nature is often richer and more wondrous thanour imagination. The diversity of alien worlds has surprised us andchallenged our preconceptions many times over.

It is quite a change from merely 20 years ago, when we knew for sure ofjust one planetary system: ours. The pace of discovery, supported by newinstruments and missions and innovative strategies by planet seekers,has been astounding.

What’s more, from measurements of their masses and sizes, we can inferwhat some of these worlds are made of: gases, ice or rocks. Astronomershave been able to take the temperature of planets around other stars,first with telescopes in space but more recently with ground-basedinstruments, as my collaborators and I have done.

Two and a half years ago, we even managed to capture the first direct pictures of alien worlds.There is something about a photo of an alien planet — even if it onlyappears as a faint dot next to a bright, overexposed star — that makesit “real.” Given that stars shine like floodlights next to the planetaryembers huddled around them, success required painstaking efforts andclever innovations. One essential tool is adaptive optics technology,which, in effect, takes the twinkle out of the stars, thus providingsharper images from telescopes on the ground than would otherwise bepossible.

At the crux of this grand pursuit is one basic question: Is our warm,wet, rocky world, teeming with life, the exception or the norm? It is animportant question for every one of us, not just for scientists. Itseems absurd, if not arrogant, to think that ours is the onlylife-bearing world in the galaxy, given hundreds of billions of othersuns, the apparent ubiquity of planets, and the cosmic abundance oflife’s ingredients. It may be that life is fairly common, but that“intelligent” life is rare.

Of course, the vast majority of the extra-solar worlds discovered todate are quite unlike our own: many are gas giants, and some are boilinghot while others endure everlasting chills. Just a handful are close insize to our planet, and only a few of those may be rocky like theEarth, rather than gaseous like Jupiter or icy like Neptune.

But within the next few years, astronomers expect to find dozens ofalien earths that are roughly the size of our planet. Some of them willlikely be in the so-called habitable zone, where the temperatures arejust right for liquid water. The discovery of “Earth twins,” withconditions similar to what we find here, will inevitably bring questionsabout alien life to the forefront.

Detecting signs of life elsewhere will not be easy, but it may welloccur in my lifetime, if not during the next decade. Given the dauntingdistances between the stars, the real-life version will almost certainlybe a lot less sensational than the movies depicting alien invasions orcrash-landing spaceships.

The evidence may be circumstantial at first — say, spectral bar codes ofinteresting molecules like oxygen, ozone, methane and water — and leaveroom for alternative interpretations. It may take years of additionaldata-gathering, and perhaps the construction of new telescopes, tosatisfy our doubts. Besides, we won’t know whether such “biosignatures”are an indication of slime or civilization. Most people will likely moveon to other, more immediate concerns of life here on Earth whilescientists get down to work.

If, on the other hand, an alien radio signal were to be detected, thatwould constitute a more clear-cut and exciting moment. Even if thecontents of the message remained elusive for decades, we would know thatthere was someone “intelligent” at the other end. The search forextraterrestrial intelligence with radio telescopes has come of agerecently, 50 years after the first feeble attempt. The construction of the Allen Telescope Arrayon an arid plateau in northern California greatly expands the number ofstar systems from which astronomers could detect signals.

However it arrives, the first definitive evidence of life elsewhere willmark a turning point in our intellectual history, perhaps only rivaledby Copernicus’s heliocentric theory or Darwin’s theory of evolution. Iflife can spring up on two planets independently, why not on a thousandor even a billion others? The ramifications of finding out for sure thatours isn’t the only inhabited world are likely to be felt, over time,in many areas of human thought and endeavor — from biology andphilosophy to religion and art.

Some people worry that discovering life elsewhere, especially if itturns out to be in possession of incredible technology, will make usfeel small and insignificant. They seem concerned that it willconstitute a horrific blow to our collective ego.

I happen to be an optimist. It may take decades after the initialindications of alien life for scientists to gather enough evidence to becertain or to decipher a signal of artificial origin. The fullramifications of the discovery may not be felt for generations, givingus plenty of time to get used to the presence of our galactic neighbors.Besides, knowing that we are not alone just might be the kick in thepants we need to grow up as a species.

 

Ray Jayawardhana, a professor of astronomy and astrophysics atthe University of Toronto, is the author of “Strange New Worlds: TheSearch for Alien Planets and Life Beyond Our Solar System.”

A version of this op-ed appeared in print on March 27, 2011, on page WK10 of the New York edition.