...

I kind of liked your idea for searching for ET by "looking down." The particular details re tuning forks were stupid, but... Why? Is there something I'm overlooking?

--well, storing over 50 bits in a tuning fork frequency is absurd, for one thing...

...

Perhaps a satellite in Earth orbit would be even longer lasting, and anyhow very easy to spot. My understanding is that no Earth orbits last more than about ten million years, due to air drag in low orbits and perturbations from the Moon in high orbits. --fascinating. Might even be true, but I'd like more evidence please.

...

As far as I understand they claim to be tracking everything in orbit larger than X, where X is what? The size of a golf ball? And nothing was there? Right. And that was strong evidence that there aren't any long-term orbits, since otherwise natural debris would have accumulated there, as it has around Jupiter and Saturn.

--I am unconvinced. It is not mathematically possible for any lone body to be "captured" into a high earth orbit, so any would have to have been there since formation. But if so, then it would have been eaten by the Moon, which has gradually spiraled outward from a formerly much lower orbit (probably initially only a few 1000 km up) due to tidal effects. So I would conjecture that the reason the Earth had no other satellites in the year 1940 was: if there were any initially, the moon ate them all. But if a little green man put an artificial satellite there 1 Gyr ago, it perhaps would still be there since it then would not have been eaten in the fashion I described. But if KFL is correct that no long lasting satellite orbits exist even today, then my idea is dead and would have to be heavily revised. Also if KFL is correct, then I ask him: where are the tiny satellites of Venus?

The Voyager records are expected to remain playable for at least 10 billion years, which is a respectable amount of time even by my standards.

--but you were claiming my 2 cm thick dust estimate was way too small, which seems like it would contradict this?

Anyhow, below the few centimeters of dust isn't a pristine surface, but smashed up debris of all sizes, getting gradually larger as you dig deeper. The Moon is impacted by meteors of all sizes, and is saturation-cratered.

--the moon may have formed for a few km of rocks of all sizes in top, already there at formation, not due to meteors. And then, after that short era of formation and initial blasting ended, then the rest of time (several Gyr) only sufficed to cause 2cm of dust to form on top of all that, in most places. If so, indicating decent chance of multi-Gyr survival in space (if willing to sacrifice a few cm thick outer layer) might be feasible. Or, maybe I'm wrong. How do we know which?

...

So... I doubt ET left any messages for us. Again I ask if anyone has done a search like Project Durin.

--Not that I know of, but I suspect I know a lot less than you. It's an interesting idea, but clearly neither one of us has thought it through enough. (Also, are aliens really going to work that hard to leave a Gyr message for us? Why should they want to?) If "Durin" aliens were going to make meter-size titanium balls and land them on Earth, it would seem easier for them to do other stuff instead that'd work better.