Can ET hear the sounds of Earth?

Artist's impression of the Cluster constellation
The Cluster constellation
4 July 2008
ESA’s four Cluster spacecraft have found that Earth and other planets have a way of shouting “I’m here!” to the rest of the Galaxy. However, the messages from the planets can only be heard and understood by using large radio telescopes. An alien race picking up Earth’s natural radio signals will hear a series of chirps and whistles, a bit like listening to R2-D2, the robot from Star Wars.
At present, even the most modern telescopes are not powerful enough to detect Earth-sized planets around distant stars. The same problem faces alien astronomers – searching for Earth would be like looking for a needle in a haystack. However, our planet’s radio outbursts - 10,000 times more intense than the strongest military radar signal – clearly advertise Earth’s presence.
Earth's chirps and whistles, click on the top right to listen
Scientists have known since the 1970s that planets with magnetic fields (including Earth, Jupiter and Saturn) emit strong radio signals. The emissions are generated high above each planet by the same solar particles that cause an aurora to light the sky beneath. Until now, astronomers had assumed that these radio waves travelled out into space in an ever-widening cone, like light from a torch. Thanks to Cluster, we now know this is not true.

As the bursts of radio waves washed over each spacecraft in turn, scientists could calculate their size and location. It turns out that the signals travel through space in a narrow beam. This makes it much easier to work out exactly where they are coming from. In the future, we may find alien worlds by tuning in to their chirps and whistles.

Are we alone?

 •  Life around other stars (
 •  Life beyond Earth (
 •  Life on Earth (
 •  Telltale signs (
 •  Life on extrasolar planets (
 •  COROT- Europe’s planet-seeker (
 •  Exoplanets (