This site, Hello from Earth is collecting
short text messages to be transmitted to Gliese 581d, a planet outside our Solar System that, from what we can tell, might support life. It's free to register and send a comment, but the deadline is 5pm Monday 24 August 2009 Sydney time (07:00 GMT Monday 24 August 2009).
The Gliese 581 system has at least two potentially habitable planets and the most Earth-like planet discovered so far, Gliese 581d. The Gliese 581 system is one of the best candidates for life outside our Solar System. NASA will, after the 24th, transmit the messages to Gliese 581d using the Canberra Deep Space Communication Complex in Tidbinbilla, Australia. Once the radio signal is sent, it will have to cross 20.3 light years, or 192 trillion km of interstellar space; it will take roughly until December 2029 to arrive, plus or minus a couple of months. That said, Gliese, the star that's the "sun" of the Gliese 581 system, is one of the 100 stars that are closes to Earth.
Hello from Earth is a joint project of COSMOS magazine, Australia's Department of Innovation, Industry, Science and Research, the CSIRO and NASA. It's a celebration of National Science Week in Australia, and the International Year of Astronomy. The video below explains a bit about the project, and how it all works. I'm sending a message; why don't you?