Everyone is thorough about checklists of items they want to take on long trips - fewer people worry about things they are supposed to leave behind.  But forty years ago, as the Apollo 11 astronauts were completing their checklist to leave the Moon they discovered that they had forgotten something important that wasn't supposed to return to Earth.

The astronauts had already left America's flag, the Stars and Stripes, and a plaque declaring "We Came in Peace for All Mankind" but as Buzz Aldrin climbed back into the Eagle lunar module, Neil Armstrong reminded him about a a tiny disc that contained encrypted messages.   Aldrin quickly remembered that he had it in his sleep pocket and threw it onto the Moon's Sea of Tranquility.

The tiny silicon disc had goodwill messages in native languages from world leaders. As U.S. State Department officials scrambled to solicit messages of goodwill from many nations, engineers used the latest technology in 1969 to enshrine the messages on material suitable for the harsh lunar environment. NASA officials also wanted to make it clear that this was an American accomplishment while balancing "good taste" from a world perspective, without implying U.S. sovereignty on the Moon.

Apollo 11 Silicon Disc with goodwill messages surrounding it.  Credit: SILICON DISC, LLC

One such message from Ivory Coast stated: "I also hope that he would tell the Moon how beautiful it is when it illuminates the nights of the Ivory Coast. I especially wish that he would turn towards our planet Earth and cry out how insignificant the problems which torture men are, when viewed from up there."

Another message from Eric Williams of Trinidad and Tobago warned: "It is our earnest hope for mankind, that while we gain the Moon, we shall not lose the world."

That tiny disc is now the star of its own book called We Came in Peace for all Mankind: The Untold Story of the Apollo 11 Silicon Discby Tahir Rahman.  The book looks at the messages from historical leaders such as Pope Paul VI, Indira Gandhi, and the Shah of Iran.

In a recent interview, Buzz Aldrin said, "Neil Armstrong and I almost forgot to leave the silicon disc on the Moon, but no one should forget the messages beautifully portrayed in Rahman's book 'We Came in Peace for All Mankind.' The disc will last on the lunar surface for 1000 years."