[flubert]

I wonder about satellites. How far above the earth's surface would a satellite have to be to keep atmospheric drag low enough to keep an artificial satellite in orbit for a long long time. And how big would it need to be for it to be naked eye visible at that distance. And what could be done to make it unlikely to be mistaken for a natural phenomena? Have clusters of satellites in geometric patterns? 65 Million years is a long time. That sounds like a more interesting project than the "Long Now" effort.

[crooked-v]

For something to last a really long time, you'd want to have it at one of the Lagrangian points. Have it be big and reflective - say, a tremendous expanse of reflective cloth behind a relatively small probe - and anybody with a telescope and patience will eventually spot it as a weird "star". Something shiny at a Lagrangian point will suggest something weird (compared to the non-shinyness of objects collected at the Lagrangian points of other planets), making it an obvious target for investigation by space probes.

There are actually a number of probes at the Sun-Earth and Earth-Moon L2 points already [1], because it's a perfect spot for telescopes and observatories. I don't know if any of them are big enough to easily observe from Earth, though.

[1]: https://en.wikipedia.org/wiki/List_of_objects_at_Lagrangian_...

[alphydan]

Not any Lagrangian point will do. L1, L2, L3 are unstable so a small perturbation will send your satellite away. Only L4, L5 will do under certain conditions for the mass of the satellite [0]

[0] https://map.gsfc.nasa.gov/ContentMedia/lagrange.pdf

[Baeocystin]

Anything in geosync is there* until the sun boils the oceans.

(*it will rather quickly wander from its original position, but it isn't leaving orbit or crashing down.)