KEO is the name of a proposed space time capsule which was to have been launched in 2003 carrying messages from the citizens of present Earth to humanity 50,000 years from now, when it would re-enter Earth's atmosphere. It was later delayed to 2006, then to 2007/2008, then to 2010/2011, then to 2012, then to 2013 and is currently estimated to launch in 2015.
The project KEO claims to be supported by UNESCO (who it claims voted it "Project of the 21st century"), Hutchison Whampoa, the European Space Agency, and among other institutions. Its name represents the three most frequently used sounds common to the most widely spoken languages today, /k/, /e/, and /o/.
Every person is invited to contribute to the time capsule. The contribution deadline was originally 31 December 2009, but as of 2014[update], it has been extended to end of 2014. Messages can be posted via the project's website or sent by postal mail. The organizers encourage everybody to gather messages from children, senior citizens, and the illiterate so that every culture and demographic on Earth is represented. The organization says, "All the messages received, without undergoing any censorship, will be embarked aboard KEO." The satellite has enough capacity to carry a four-page message from each of the more than six billion (as of the original 2009 deadline) inhabitants on the planet.  Once the satellite is launched, the messages will be made freely available on the web.
KEO, a space time capsule, will also carry a diamond that encases a drop of human blood chosen at random and samples of air, sea water, and earth. The DNA of the human genome will be engraved on one of the diamond's facets. The satellite will also carry an astronomical clock that shows the current rotation rates of several pulsars, photographs of people of all cultures, and "the contemporary Library of Alexandria", an encyclopaedic compendium of current human knowledge.
The messages and library will be encoded in glass-made radiation-resistant DVDs. Symbolic instructions in several formats will show the future finders how to build a DVD reader.
The satellite itself is a hollow sphere 80 cm in diameter. The sphere is engraved with a map of Earth and surrounded by an aluminium layer, a thermal layer and several layers of titanium and other heavy materials intertwined with vacuum. The sphere is resistant to cosmic radiation, atmosphere re-entry, space junk impacts, etc. For its first few years in orbit, KEO will sport a pair of wings 10 meters across that will aid in its spotting from Earth. As the satellite enters the atmosphere, the thermal layer will produce an artificial aurora to give a signal of the satellite's re-entry. The passive satellite will not carry any communications or propulsion systems. It will be launched by an Ariane 5 rocket into an orbit 1,800 km high, an altitude that will bring it back to Earth in 500 centuries, the same amount of time that has elapsed since early humans started to draw in cavern walls.
The project KEO was conceived in 1994 by French artist-scientist Jean-Marc Philippe, a pioneer of space art. Messages began to be collected, and an initial launch date was set for 2001. Technical feasibility demonstration and other various delays have moved the launch date to 2015.
Several previous spacecraft have included time capsules for humans (or aliens) in the far future. Part of the Apollo 11 Lunar Module, still on the moon, includes a plaque showing the arrangement of the Earth's continents in 1969. The LAGEOS satellite (which will re-enter the atmosphere in 8.4 million years) contains a plaque showing the arrangement of the Earth's continents in the past, present, and future. Pioneer 10 and Pioneer 11 both contain plaques that give pictorial information about their time and place of origin. Most famously, the two Voyager spacecraft each contain a golden record that contains pictures and sounds of Earth, along with symbolic directions for playing the record and data detailing the location of Earth. The Pioneers and Voyagers have left the solar system for interstellar space. In 2004, the Long Now Foundation produced a nickel disk containing parallel texts in over a thousand languages, which was launched aboard the Rosetta.
- Life After People: The series, Episode 13 "Crypt of Civilization" mentions KEO as one of the last time capsules in the universe.
- Bridges, Andrew (31 July 2000). KEO: The 50,000-Year Mission to Earth Space.com
- Stenger, Richard (29 August 2000). KEO time capsule could remain in orbit until 52001 AD CNN.com
- HowStuffWorks.com (5 September 2000). Time Capsule to Orbit Earth for 50,000 Years HowStuffWorks.com
- The Hindu Business Line (29 August 2002). Hutch brings space-time capsule project to India The Hindu Business Line
- ChennaiOnline.com (4 September 2002). KEO, a time capsule in space! ChennaiOnline.com
- Ashraf, Syed Firdaus (15 October 2003). Once upon a time, 50,000 years ago... Rediff.com
- EUROPA (28 May 2004). New satellite carries hopes and dreams of humanity EUROPA
- Message To Earth's Future (1 June 2009) Message To Earth's Future The Wondrous
- Wayne, Gregory (9 August 2011). A Short History of Long-Term Thinking for Our 50,000 Year Time Capsule Motherboard