The search for ET continues — in West Virginia

May 15, 2011 by Amara D. Angelica

Robert C. Byrd Green Bank Telescope (GBT), the world's largest fully steerable single-aperture antenna (credit: NRAO)

Now that NASA’s Kepler space telescope has identified 1,235 possible planets around stars in our galaxy, astronomers at the University of California, Berkeley, are aiming a radio telescope — the 100 meter Robert C. Byrd Green Bank Telescope, the largest steerable radio telescope in the world — at the most Earth-like of these worlds to see if they can detect signals from an advanced civilization.

“The SETI Institute is also checking out the most attractive of the new worlds discovered by Kepler, in hopes of discovering that some might shelter — not just life — but technically sophisticated life,” SETI Institute senior astronomer Seth Shostak told KurzweilAI. :”We do this over a very wide range of radio frequencies, and with the ability to immediately check out any interesting signals. The real excitement, of course, is that SETI practitioners now have some very compelling directions in which to aim their antennas. Really, it’s like trying to discover Antarctica two centuries ago: the chances improve when everyone aims their ships toward the south!”

The search began on a week ago on May 8, when astronomers dedicated an hour to eight stars with candidate planets in the star’s habitable zone (ones with a surface temperature between zero and 100 degrees Celsius, so liquid water could be maintained and they are likely to harbor life).

They plan to acquire 24 hours of data on a total of 86 Earth-like planets, do a coarse analysis, and then, in about two months, ask an estimated 1 million users of SETI@home (the world’s largest distributed computer) to conduct a more detailed analysis on their home computers.

Targeting habitable planets

The Kepler Spacecraft (credit: NASA Ames Research Center)

The Kepler Mission uses a satellite to watch for the small dip in light received from a star when an orbiting planet passes between our line of sight with the star.

So far, around 1300 planet candidates have been found by the Kepler Satellite.

The 86 stars were chosen from the 1,235 candidate planetary systems, called Kepler Objects of Interest, or KOIs. The targets include the 54 KOIs identified by the Kepler team as being in the habitable temperature range and with sizes ranging from Earth-size to larger than Jupiter.

There are also 10 KOIs not on the Kepler team’s habitable list but with orbits less than three times Earth’s orbit and orbital periods greater than 50 days, and systems with four or more possible planets.

(Credit: NASA Ames Research Center)

Locations of Kepler's planet candidates by size (credit: NASA/Wendy Stenzel)

After the Green Bank telescope has targeted each star, it will scan the entire Kepler field for signals from planets other than the 86 targets. “If you extrapolate from the Kepler data, there could be 50 billion planets in the galaxy,” physicist Dan Werthimer, chief scientist for SETI@home, said. “It’s really exciting to be able to look at this first batch of Earth-like planets.”

Why the Green Bank Telescope?

Werthimer conducted a brief SETI project using the Allen Telescope Array (ATA), which hosted a broader search for intelligent signals from space run by the SETI Institute. That search ended last month after the institute and UC Berkeley ran out of money to operate it. Now the action has moved to West Virginia.

So why not use Arecibo? Because the Arecibo dish can’t view the area of the northern sky on which Kepler focuses. Arecibo also has limited frequency coverage (it centers on the 21 centimeter or 1420 MHz “water hole,” a natural window in which water-based life forms would signal their existence, since its wavelengths easily pass through the dust clouds that obscure much of the galaxy).

“With a new data recorder on the Green Bank telescope, we can scan a 800 megaHertz range of frequencies simultaneously, which is 300 times the range we can get at Arecibo,” said Werthimer. One day on the Green Bank telescope provides as much data as one year’s worth of observations at Arecibo: about 60 terabytes.

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