TIME The Sh for Life in Our Universe

TIME

THE SEARCH FOR LIFE IN THE UNIVERSE

Contents

The search for other worlds is coming up roses

Astronomers use a bag of tricks to detect exoplanets

The search for extraterrestrial life could use a boost

Looking for aliens is just another day at the office

Powerful new telescopes are spilling cosmic secrets

Looking for life in our own solar system

Highlights from more than a half-century in space

Recognizing alien life-forms may not be easy

Do comets and meteorites seed the cosmos with life?

Life thrives in the most inhospitable places

If an ET arrives, will we roll out the welcome mat?

We use aliens to fill some very human needs

A cavalcade of space creatures, wacky to woeful

The existential bummer of finding nothing

Parts of this book were previously published in TIMEs New Space Discoveries and in TIME magazine .

THE GREAT CANARY TELESCOPE , which began scientific observations in 2009 in the Canary Islands, is the worlds largest single-mirror optical telescope.

Waiting for a sign

BY MICHAEL D. LEMONICK

WHEN THE SUBJECT OF extraterrestrials comes up in polite conversation, any scientist whose lonely lifes work is listening for distant radio signals often has to deal with what Seth Shostak of the SETI Institute calls the giggle factor. And to be fair, amid a backdrop of The X-Files and The Twilight Zone and conspiracy nuts convinced the Air Force has aliens on ice in Area 51not to mention those who figure visitors from space must have built the pyramidseven learned men can begin to sound ridiculous. Besides, no one has heard or seen anything so far, have they?

Yet whether life exists on planets other than ours is a scientific and philosophical issue of real import, its pedigree far older than many realize. As early as the sixth century B.C., the Pythagoreansmathematically inclined philosophers (in other words, serious Greeks)thought the moon hosted lush plant and animal life. In the 15th century A.D., German astronomer Nicholas of Cusa suggested that many stars and parts of the heavens are inhabited. In 1600 the Italian Giordano Bruno was burned at the stake for, among other things, saying, The countless worlds in the universe are no worse and no less inhabited than our Earth. And astronomer William Herschel (1738 1822), discoverer of Uranus and inventor of many modern astronomy techniques, believed that the moon, Mars and even the sun were home to sentient beings.

Sure, even smart people can be very wrong. Still, by the late 1800s, the notion that other planets in our solar system were home to life of one sort or another was more or less mainstream, egged on by Giovanni Schiaparelli, an Italian astronomer who uncovered what seemed to be visual confirmation. Peering through his telescope at Mars, he made out ruts that crisscrossed the planet. Canali, he called themchannelswhich he incautiously interpreted to be waterways dug by Martians to support their agriculture.

Soon after, Boston aristocrat Percival Lowell sank much of his wealth into building a private observatory in Arizona. He saw the canals too, and because of his man-of-letters reputationnot only did he go to Harvard, his brother was its presidenthis findings were trumpeted as fact.

They werent, of course. The canals were an optical illusion, the result of too much squinting through a too-weak telescope. And in the aftermath of Lowells public humiliation, all talk of alien life was avoided by the scientific community for decades, consigned to fiction writers such as H.G. Wells and Edgar Rice Burroughs.

The rationally curious couldnt stay gun-shy forever, though. For many, the idea that life is unique to a single location in a universe billions of light-years wide seemed just too far-fetched. And in 1959, in a paper published in Nature , the Cornell University physicists Philip Morrison and Giuseppe Cocconi argued that near some star rather like the sun there are civilizations with scientific interests and with technical possibilities much greater than those now available to us. It would be foolish not to search for the inevitable signals of these civilizations. The probability of success is difficult to estimate, they wrote, but if we never search, the chance of success is zero.

Search parties were quick to convene. From the start, scientists were resigned to the fact that advanced alien civilizations, if they existed, would be the rarest form of life in the cosmos. Evolution, the thinking went, doesnt necessarily progress in a particular direction. Single-celled organisms are almost certainly the first step, but what happens after could vary wildly, depending on local conditions. On Earth, it took some 2 billion years for single cells to evolve into multicellular organisms. On another world, it might take much longer, or it might not happen at all. On Earth, mammals began to flourish only after the dinosaurs were wiped out by an asteroid. But had that asteroid scooted by our planet instead of smashing into it, giant lizards might still be dominating the land.

So astrobiologists are thinking small, figuring the first extraterrestrial life they find will be simple, bacteria-like organisms, just because theyre likely to be the most common specimens. Maybe theyll be in the soil of Mars or the subsurface oceans of the moons Europa (Jupiter), Enceladus (Saturn) or Ganymede (Jupiter). Maybe well know them only by their waste gases circulating in the atmosphere of a distant exoplanet.

Then again, maybe an ET radio signal or laser beam is even now racing toward us at light speed. So dont be surprised if the millennia-old question of whether were alone is resolved in the next decade or two by a new army of telescopes, probes and rovers. Unless, of course, it is answered with an electromagnetic ping the day after tomorrow.

Triumph of the Planet Hunters

Recent discoveries suggest that our galaxy contains billions of Earth-size worlds. Now astronomers are narrowing the searchfor planets that most closely resemble ours in the particular ways that support life

BY MICHAEL D. LEMONICK

BESIDE A MODEL of the Kepler spacecraft at NASAs Ames Research Center, William Borucki, the missions chief scientist, lectures on the space observatory, which orbits the sun in search of distant Earth-like planets.

LOOK UP ON A CLEAR, MOONLESS night, far from city lights, and you can see thousands of stars twinkling in the dark vault of the sky. Astronomers, of course, will assure you that the stars arent really twinkling. Rather, its an illusion caused by the shimmering of Earths atmosphere, something like the rippling air you see coming off the hood of a car on a hot summer day.

In fact, many stars are twinkling, if only in a way that a clear-eyed telescope orbiting high above the atmosphere can make out. More precisely, the stars are winking at us, dimming just a bit on a schedule as precise as clockwork. Others are wobbling in place, moving toward us and away, then back again with the same sort of rhythm.

The explanation for all this winking and wobbling is that most stars arent drifting through the Milky Way in solitude. Theyre accompanied by planets, just as the sun is; those winks and wobbles are proof of that. When a planet passes precisely in front of its star from Earths point of view, the star dims subtly. Even when things arent lined up quite so perfectly, the planets gravity tugs the star to and fro as it orbits, causing measurable changes in starlight.