IF WE want to pick up messages from intelligent aliens, we need to listen at the right time. Our best chance of picking up an ET broadcast is when the Earth is closest to being directly between our Sun and the transmitting alien star, according to Robin Corbet of the Universities Space Research Association.
Not only does that position minimise any interference from the Sun in the signal, but it also has a psychological significance 鈥� that鈥檚 when we鈥檙e technically closest to the aliens, even if it鈥檚 only by a tiny fraction of the distance between us.
We鈥檙e not deliberately trying to attract the attention of alien civilisations, but we do listen out for signals that they might be trying to send us. But the sky is so big it鈥檚 like looking for a needle in an infinitely large haystack.
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Corbet reasons that the sender would pick a time they think is significant. That way, they wouldn鈥檛 have to keep their transmitter switched on all the time and would save enormous amounts of energy. Short periods of signalling might also help keep up the aliens鈥� morale. 鈥淭he longer a programme is continued without success, the less resources a civilisation may be willing to devote to it,鈥� says Corbet.
Aliens would determine the Earth鈥檚 orbit, according to Corbet, then time their signal to arrive when Earth is closest to them. All we need to do is synchronise our searches to look at possible sources of signals at these times ().
We are trying to second-guess ET ourselves, as we have chosen to limit our search to signals using a wavelength corresponding to hydrogen, the simplest and most plentiful element in the Universe (see Graphic).
Other astronomers think the type of focused search proposed by Corbet is definitely worth pursuing. 鈥淭hey could save time and greatly increase our chances of picking up ET,鈥� says David Hough of Trinity University in San Antonio, Texas.