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The social networking site is running a competition which will see 500 winners get the chance to send a message of their choice 20.5 light years to the planet Gliese 581c, considered by scientists to be most like our own in atmosphere and temperature.

Rather than sending an actual probe, which would cost a huge amount to launch and take many hundreds of years to reach its destination, the messages will be broadcast by the National Space Agency of Ukraine's RT-70 radio telescope.

Users have until 30 September to submit a message, with the winning entries being transmitted on 9 October. A short video describing the project can be seen here.

However, even if the planet is teeming with intelligent life, unless they are listening closely the brief transmission will be lost when it arrives in 2029. Of course, this may be a blessing, as they may not appreciate receiving interplanetary spam.