[ericbarrett]

The Lunar Orbiter Laser Altimeter has mapped the lunar surface to, best as I can tell from a quick search, about 1m resolution. So I think a reasonably sized stele or 2001-style monolith would probably have been discoverable at our current tech level.

[midasuni]

But we wouldn’t be able to detect human level lunar activity in a million years time.

We can barely detect human activity from 50 years ago when we know exactly where it is.

I think we are More likely to spot ancient Geostationary satellites, which will have drifted away from a perfect circle but should still be noticeable. LAGEOS aren’t in anywhere near that high an orbit but should survive 8 million years. They have a plaque on them designed by Sagan should a future civilisation find them.

[ericbarrett]

You’re right about satellites but I think you’re underestimating how long a monolith could last on the Moon. For something big and built to last, it could be many many millions of years https://bigthink.com/starts-with-a-bang/astronaut-footprints...

[midasuni]

But we haven’t put anything built to last on the moon - rovers and landing stages are very small and relatively fragile

A similar civilisation may have gone to the moon, but thanks to irradiation and micrometeorites over millions of years. Footprints and tyre tracks would certainly be gone, and while you could land at an Apollo landing site and detect remains of refined metal, it’s unlikely to be something you could see from orbit with our level of equipment, you’d have to get up close and personal, and we haven’t done that.

[smegger001]

How long would it survive as a monolith on the surface before it would appear to be another boulder? How long until it is illegible due to micrometorite abrasions?

[eschaton]

The “2001” monolith was heavily implied to have been explicitly buried. It was detected first as a magnetic anomaly, and when touched while exposed to sunlight it emit an enormous RF burst.

In other words, it was specifically protected from the elements, in a way intended to be detected only by a species at a certain minimum level of technological development.