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ET’s nightlife could be a giveaway

Artist's impression of an alien planet showing city lights

If an alien civilisation builds brightly-lit cities, like those shown in this artist's conception, future generations of telescopes might allow us to detect them. This would offer a new method of searching for extraterrestrial intelligence elsewhere in our Galaxy.

IN THE SEARCH FOR EXTRATERRESTRIAL INTELLIGENCE, astronomers have hunted for radio signals and ultra-short laser pulses. But in a new proposal, Avi Loeb (Harvard-Smithsonian Centre for Astrophysics) and Edwin Turner (Princeton University) suggest a new technique for finding aliens—look for their city lights.

“Looking for alien cities would be a long shot, but wouldn’t require extra resources. And if we succeed, it would change our perception of our place in the universe,” said Loeb.

As with other SETI methods, they rely on the assumption that aliens would use Earth-like technologies. This is reasonable because any intelligent life that evolved in the light from its nearest star is likely to have artificial illumination that switches on during the hours of darkness.

Telling night from day

How easy would it be to spot a city on a distant planet? Clearly, this light will have to be distinguished from the glare from the parent star. Loeb and Turner suggest looking at the change in light from an exoplanet as it moves around its star.

As the planet orbits, it goes through phases similar to those of the Moon. When it’s in a dark phase, more artificial light from the night side would be visible from Earth than reflected light from the dayside. So the total flux from a planet with city lightingwill vary in a way that is measurably different from a planet that has no artificial lights.

Artist's impression of Pluto

Current technology could spot city lights on Pluto (artist's impression).

Spotting this tiny signal would require future generations of telescopes. However, the technique could be tested closer to home, using bodies at the edge of our Solar System.

Closer to home?

Loeb and Turner calculate that today’s best telescopes ought to be able to see the light generated by a Tokyo-sized metropolis at the distance of the Kuiper Belt—the region occupied by Pluto, Eris, and thousands of smaller icy bodies. So if there are any cities out there, we ought to be able to see them now.

By looking, astronomers can hone the technique and be ready to apply it when the first Earth-sized worlds are found around distant stars in our galaxy.

“It’s very unlikely that there are alien cities on the edge of our Solar System, but the principle of science is to find a method to check,” Turner said. “Before Galileo, it was conventional wisdom that heavier objects fall faster than light objects, but he tested the belief and found they actually fall at the same rate.”

As our technology has moved from radio and TV broadcasts to cable and fibre optics, we have become less detectable to aliens. If the same is true of extraterrestrial civilisations, then artificial lights might be the best way to spot them from afar.

Adapted from information issued by Harvard-Smithsonian Centre for Astrophysics. Images by David A. Aguilar (CfA) and ESO.

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SETI’s 50th anniversary

Allen Telescope Array

The SETI Institute has conducted a new "listening" study of five target stars using the Allen Telescope Array (ATA), located in northern California.

  • 50 years since first project to find extraterrestrials
  • SETI involves listening for signals from alien civilisations
  • New worldwide campaign begun

This week astronomers from twelve countries on six continents marked the 50th anniversary of the search for extraterrestrial intelligence (SETI) by beginning a coordinated series of observations of several nearby stars—including two stars that were the target of the first search.

To demonstrate the advances in SETI over the past half century, on November 5, 2010, astronomers in Australia, Japan, and Korea began observations for radio and laser signals from civilisations circling these stars, followed over the next day by SETI searches in Italy, the Netherlands, France, Argentina, and the United States. Additional observations will take place in late November 2010.

SETI pioneer Frank Drake

SETI pioneer Frank Drake

The first SETI experiment, Project Ozma, was conducted in April 1960 by astronomer Frank Drake, now at the SETI Institute in Mountain View, California. Project Ozma—named after the book “The Wonderful Wizard of Oz”—listened for radio signals from extraterrestrial civilisations and started a new field of science.

To commemorate this first search and the advances in SETI science and technology over the past half century, astronomer Shin-ya Narusawa of Nishi-Harima Astronomical Observatory in Japan launched Project Dorothy, named after the heroine of the same story.

“It is thrilling for me to witness the beginnings of Project Dorothy, the continuation of my search of fifty years ago,” said Drake. “To have so many talented people using so many telescopes in this new search, with the electronics and computer equipment of today, is a joyful thing to me.”

“The equipment of today is far better than what we could have fifty years ago, and will result in both very much better and very much more data than could be obtained then.”

“Two of the original stars from Project Ozma—Tau Ceti and Epsilon Eridani—are the nearest solar-type stars in the northern hemisphere,” explained Narusawa. “Therefore, these two stars were the best SETI targets a half century ago. They remain the symbol of project Ozma and are two of the target stars for Project Dorothy.”

“But astronomy has improved over the last five decades, and about five hundred planets have been discovered around other stars,” he added. “Some of these stellar systems have planets located the right distance from their stars to support life. We also included such stars among the targets of Project Dorothy.”

ATA dish at night

SETI—the Search for Extraterrestrial Intelligence—involves listening for signals at radio or laser wavelengths.

“Project Dorothy vividly demonstrates just how far SETI has come in the past fifty years,” said the SETI Institute’s Douglas Vakoch, who is a member of Project Dorothy’s Working Group.

“Astronomers can now do SETI research at observatories from South Africa to the Netherlands, from Argentina to India, from Japan to Italy, as well as from the longstanding American projects at the SETI Institute, the University of California at Berkeley, and Harvard University,” Vakoch explained.

“The lessons learned through Project Dorothy provide critical preparation for the day we finally detect a signal from another civilisation.”

Because of the daily rotation of the Earth, many stars are visible for only a portion of the day from a single observatory.

“By learning how to coordinate international SETI observations now, we’ll be better prepared to track a signal continuously, around the world, after first contact,” Vakoch added.

“Over the past 50 years our searches have not yet produced the discovery we all hope for,” said Drake. “This is understandable—in our vast and awesome universe it will take long, painstaking, and comprehensive searches before we will have a good chance of success.”

“This is the major lesson learned from previous searches. Project Dorothy is a major step in meeting the challenge created by this lesson.”

Adapted from information issued by SETI Insitute.

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