More than 3,700 contributions from 146 countries and regions were collected by the international project involving the University of Edinburgh, European Space Agency and European Southern Observatory.
They range from responses full of optimism and hope for the future of humanity to more downbeat themes concerning climate change and war.
More than 100 participants spoke about people colonising other worlds.
Edinburgh College of Art postgraduate student and lead organiser Paul Quast said: “It has been a humbling experience attaining the thousands of contributions from different countries.
“The huge interest reflects a promising worldwide shift in attitudes for securing a future for Earth, its biosphere and humankind.
“Hopefully, this momentum can be sustained as the messages travel through interstellar space for the next several hundred years.”
The messages will be broadcast at 9pm UK time from a dish antenna at the European Space Agency’s Cebreros Deep Space Tracking Station in Spain.
They will take less than six minutes to pass deeper into space than Mars. Within 21 hours the signal will have travelled further than Voyager 1, the spacecraft launched in 1977 that is now heading out of the solar system.