From Gwydion Williams
Gregory Benford asks for suggestions for what to put on a plaque that may be sent to Titan and perhaps discovered in a billion years (This Week, 18 February).
For this “message to the unknown future”, one surely needs something that will let it be precisely dated by future discoverers. The exact relative positions of all the planets and moons on, say, January 1st 1997 should tell them that – the combination ought to be unique. As back-up, one could add some details of the stars of the Plough, and of the fast-changing Orion Nebula, and perhaps the Crab Nebula and its pulsar.
For a longer-term perspective one might include the present position of the Magellanic Clouds as they orbit the Milky Way, and of Andromeda and other galaxies of the Local Group, or even the Virgo Super-cluster. Present-day astronomers would dearly like to know what they looked like a billion years ago, wouldn’t they?
As well as that, the disc should store details of the current temperatures and gaseous compositions of all the moons and planets, along with current changes going on on our planet. So if the future inhabitants of Titan find Earth as hot as Venus, they will at least be able to guess why.
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