Space
The footprints left on the Moon could last for millions of years.
The Moon has no wind, no rain and no flowing water to disturb the surface. The boot prints from the Apollo landings are still there, exactly as they were made.
Why is this true?
The only thing slowly erasing them is the constant rain of micrometeorites, which wears the surface down at a rate of roughly a millimetre every million years.
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More about space
Space facts are mostly a lesson in scale. Days longer than years, storms wider than Earth, light that left its star before the pyramids existed — the numbers stop being intuitive very quickly. Every entry here comes from established astronomy and includes a short explanation of what causes the effect, so the fact holds up when someone asks the obvious follow-up question at the dinner table.