Taking aim to find out if anyone out there is calling

Ken Tappings' weekly astrophysics column from the Herzberg Institute


This week’s subject was triggered by an email from a colleague at the National Research Council. Like many things it is totally logical, when one thinks about it – afterwards.

The main way we search for intelligent aliens is to look for their radio signals.  We point big antennas and sensitive receivers at candidate stars believed to have planets and look for the sort of signals that are unlikely to be of natural origin. The chances of success are tiny because we have to be pointing at the right star, at the right time, and have our radio receiver tuned to the right frequency. We now have receivers that can monitor many frequencies simultaneously, and check many stars at a time. However, the odds are still tiny. That email pointed out a method to significantly improve those odds.

The idea is simple; we point our antennas in the direction of aliens likely to have their antennas pointed in our direction. That sounds like crystal ball stuff, but it isn’t. A decade or two ago, this would have been impossible, but not today.

We are now pretty good at detecting planets orbiting other stars; the count is now in the thousands. The technique we use is to monitor the brightness of other stars, which we can now do simultaneously for thousands of stars, and look for minute dimming of the starlight as a planet moves in front of the star. Let’s assume our alien friends are using the same technique, and then point their transmitting antennas in the direction of stars they know to have planets.

All the planets in our Solar System lie more or less in the same plane, like marbles rolling around a plate, with the Sun in the centre. We call this plane the ecliptic. To detect our planets, our aliens will have to see them pass in front of the Sun, which means they must live on a planet orbiting a star that lies very close to the plane of the ecliptic. Therefore, we should point our antennas at stars we know to have planets, and which lie close to the plane of the ecliptic.

Searches like this are not really for intelligent aliens; they are searches for intelligent aliens who are using radio. We live in a radio world. In addition to broadcasting, radar and satellite navigation systems, we now carry one or more radio devices on our persons. Our civilization is tied together by radio technology. It is easy to forget that this might not be the case for alien civilizations.

Intelligent races living under water would not be heavy users of electricity or radio. It might also be that they have found better means to communicate, using technologies we have not yet dreamed of. On the other hand, radio is what we are stuck with at the moment, and probably we would have more in common with aliens using at least somewhat similar technologies to ours. Evidence even here on Earth shows life can take many bizarre forms, and this is probably the case across the universe. It is likely that we will have little in common with many of the civilizations sharing our universe. However, if we make no assumptions at all about what we seek, we are not going to get anywhere.

Mars and Saturn dominate the southwestern sky.  Venus and Jupiter lie close together in the eastern sky before dawn. The Moon will be new on the 18th.

Ken Tapping is an astronomer with the National Research Council’s Dominion Radio Astro-physical Observatory, Penticton.