Radio telescopes designed to study the primordial universe could also eavesdrop on extraterrestrial civilisations similar to our own. "By a happy accident," says abraham Loeb of Harvard University, "the telescopes will be sensitive to justthe kind of radio emission that our civilisation is leaking into space."
The next generation of radio telescopes are designed to pick up radio waves emitted by neutral hydrogen molecules in the early universe. These signals originally had a wavelength of 21 centimetres, but the universe has expanded since they were emitted, stretching the waves in the process. Today, these signals have a wavelength of several metres, corresponding to a frequency of tens or hundreds of megahertz. "This overlaps with our civilisation's radio emissions, which are in the range 50 to 400 megahertz," says Loeb.
Loeb and his Harvard colleague Matias Zaldarriaga say that the most powerful emissions from our own planet come from military radars, and TV and FM radio transmitters. They span a small range of frequencies, and if ET is producing similar signals, these "spikes" in the radio spectrum will be discernible by telescopes such as the Low- Frequency array (LoFaR) which is now being built in the Netherlands (http://www.arxiv.org/abs/astro-ph/0610377). "This is radio SETi, but at wavelengths that SETi experiments haven't probed in the past," says Seth Shostak of the SETi institute in Mountain View, California. "That by itself is reason enough to recommend it."
The ability of telescopes such as LoFaR to detect spectral spikes means they will also be able to detect the doppler shift in wavelength as an ET planet orbits its parent star. according to Loeb and Zaldarriaga, this will make it possible to deduce the shape of the orbit, the tilt of the planet as it spins on its axis, and the planet's distance from the star. "This in turn will allow an estimate of the planet's surface temperature, indicating whether liquid water is a possibility," he says.
Loeb and Zaldarriaga say that the technique would pick up radio leakage from alien civilisations within about 1000 light years of Earth. By some estimates, there could be as many as 100 million stars with planets within this volume of space. Of course, the success of Loeb and Zaldarriaga's proposal depends crucially on how many of these planets have civilisations that are roughly at the same stage of development as ours. "This is very difficult to quantify," says Loeb.
There are practical difficulties, too. "By looking in the bands that we humans fill with signals – radar, TV and so on – the SETi researchers are guaranteed to encounter enormous terrestrial interference," Shostak says. Sorting out ET from the BBC will be a substantial challenge."
Written by Marcus Chown
EMBARGOED UNTIL WEDNESDAY 25 OCTOBER 2006 14:00 ET US (18:00 HRS GMT)
"This article is posted on this site to give advance access to other authorised media who may wish to report on this story, or quote extracts as part of fair dealing with this copyrighted material. Full attribution is required, and if reporting online a link to www.newscientist.com is also required. This story posted here is the EXACT text used in New Scientist magazine, therefore advance permission is required before any and every reproduction of each article in full. Please contact firstname.lastname@example.org. Please note that all material is copyright of Reed Business Information Limited and we reserve the right to take such action as we consider appropriate to protect such copyright."
THIS ARTICLE APPEARS IN NEW SCIENTIST MAGAZINE ISSUE: 28 OCTOBER 2006
EDITOR'S NOTE: PRIOR PERMISSION IS REQUIRED BEFORE ANY REPRODUCTION OF THIS STORY IN FULL
IF REPORTING ON THIS STORY, PLEASE MENTION NEW SCIENTIST AS THE SOURCE AND, IF REPORTING ONLINE, PLEASE CARRY A HYPERLINK TO: http://www.newscientist.com
UK CONTACT - Claire Bowles, New Scientist Press Office, London:
Tel: +44(0)20 7611 1210 or email email@example.com
US CONTACT – New Scientist Boston office:
Tel: +1 617 386 2190 or email firstname.lastname@example.org
AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert! system.