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Search for Other Earths @ National Geographic Magazine
   
By Tim AppenzellerPhotographs by Mark Thiessen



In an astronomical breakthrough, scientists are discovering planet after planet circling distant stars as the search narrows for a world like our own.



Get a taste of what awaits you in print from this compelling excerpt.

It's past midnight in the dim telescope control room, but Dominique Naef's day has suddenly brightened. He twitches his computer cursor over a wavy line. "I like it," the Swiss astronomer says, beaming. "I like it a lot. Wow."
 
Fifty light-years away in the night sky, a star like our sun is doing a stately dance, stepping toward Earth and away again. From the La Silla Observatory in the mountains of Chile, Naef and his colleagues have stolen glimpses of the dance for months. But for much of that time their view was blocked by clouds, a foot of snow, and, this August night—midwinter in Chile—humidity so high that the telescope dome had to be shut to keep out frost. Earlier in the evening, between cups of espresso and cigarette breaks, Naef gloomily eyed a display of weather data. He feared another lost night.
 
Then the humidity dropped, and the telescope operator gave the go-ahead. Naef and Christoph Mordasini, a graduate student from Bern, huddled at their screens. They captured one more reading of the star's motion before, minutes later, the humidity shot up again and the operator called a halt for the night.
 
It's just another glimpse, but it's enough to turn a suspicion into a near certainty. The excited jiggle of Naef's cursor shows that the reading has fallen just where it should if an unseen planet is tugging the star to and fro. The next day the team leader, veteran planet hunter Michel Mayor of the University of Geneva, decides that it's time to announce the discovery. If it stands up to the scrutiny of other scientists, this planet, around a star called Mu Arae, will be a milestone in the quest for another Earth.


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Multimedia
Watch how planets are formed through a process called disk instability.

Multimedia
Glide through space in this artistic conception of a giant ringed planet and its earth-sized moon.

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Should an Earth-like planet be found, do you think it will harbor life? How would such a discovery affect our philosophies, religions, and our perceptions of ourselves?



More to Explore

In More to Explore the National Geographic magazine team shares some of its best sources and other information. Special thanks to the Research Division.

Did You Know?
Infinite Worlds

Four hundred years ago an advocate of the idea that planets orbited stars other than our sun was burned at the stake.  Giordano Bruno, a rebellious, independent Dominican monk (until he was kicked out of the order) further infuriated religious leaders by asserting in the late 16th century that beings like men inhabited these other worlds.

Earlier philosophers pondered the plurality of worlds with less dire consequences. In fifth-century B.C. Greece, atomists, men who proposed that reality consisted of indestructible atoms and the empty space around them, emerged. Little remains of the writings of Leucippus, thought to be the originator of atomist philosophy, but we know his student Democritus proposed:

"There are innumerable worlds which differ in size. In some worlds there is no sun and moon, in others they are larger than in our world, and in others more numerous. They are destroyed by colliding with each other. There are some worlds without any living creatures, plants, or moisture."

Inspired by the atomists, the epicurians, who stressed the intellectual pleasures of natural science, furthered the thinking on alien worlds in the late fourth and early third centuries B.C. Epicurus, the founder, summarized his teachings in a letter to Herodotus:

"There is an infinite number of worlds, some like this world, some unlike it. For the atoms being infinite in number, as has just been proved, are borne ever further in their course. For the atoms out of which a world might arise, or by which a world might be formed, have not all been expended on one world or a finite number or worlds, whether like or unlike this one. Hence there will be nothing to hinder an infinity of worlds."

Aristotle came along with a one-liner in his On the Heavens (Book 1, chapter 8) in the middle of the fourth century B.C.: "There cannot be more worlds than one." The debate continued for some 1,300 years until the discovery of planets around a sunlike star in 1995. It must be heartening to today's thinkers, planet-hunters, and biologists that they pursue their dream of finding a planet like our own around another sun without fear of burning at the stake.

—Barbara W. McConnell
Did You Know?

Related Links
Extrasolar Planets Encyclopedia
cfa-www.harvard.edu/planets/
A source for the latest news about planets orbiting other stars. The site includes links to valuable information about the search for extrasolar planets.
 
NASA Space Science
spacescience.nasa.gov/missions/index.htm
Follow links for the Kepler, SIM, and TPF missions, all dedicated to detecting extrasolar planets.
 
W. M. Keck Observatory
www2.keck.hawaii.edu/geninfo/about.html
The powerful Keck telescopes reveal the faintest objects beyond our solar system.
 
Telescopes in Chile
www.circuloastronomico.cl/observatorios/observatorios.html#3
Find links to observatories, including La Silla and the Very Large Telescope, involved in the extrasolar planet hunt.
 
Large Binocular Telescope
medusa.as.arizona.edu/lbto/
A telescope with dual mirrors, now under construction, will soon be contributing to our knowledge of other solar systems.

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Bibliography
Croswell, Ken. Planet Quest: The Epic Discovery of Alien Solar Systems. The Free Press, 1997.
 
Laughlin, Greg, and Tim Castellano. "Join the Hunt." Astronomy (January 2003), 55-8.
 
Lunine, Jonathan I. Earth: Evolution of a Habitable World. Cambridge University Press, 1999.
 
Mayor, Michael, and Pierre-Yves Frei. New Worlds in the Cosmos: The Discovery of Exoplanets. Cambridge University Press, 2003.
 
Seager, S. "The Search for Extrasolar Earth-like Planets," Earth and Planetary Science Letters (208), 113-124.

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NGS Resources
Achenbach, Joel. "Dust in Space," Who Knew? National Geographic (March 2004).
 
Achenbach, Joel. "Life Beyond Earth." National Geographic (January 2000), 24-51.

Skurzynski, Gloria. Are We Alone? Scientists Search for Life in Space. National Geographic Books, 2004.

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