As much as the idea appeals to me I find it difficult to see how evidence of prior spacefaring civilizations would not be visible in orbit or on moons etc. How long will the US flag on the moon survive? Now imagine entire bases on bodies where almost no erosion occurs. Not to mention artifacts in orbital space, where preservation is effectively for ever. If a satellite was in geostationary orbit around Venus or Mars, how long would it remain in place? Forever? Or are there mechanisms that will inevitably disturb it?
Quote from: M.E.T. on 04/29/2017 03:36 pmAs much as the idea appeals to me I find it difficult to see how evidence of prior spacefaring civilizations would not be visible in orbit or on moons etc. How long will the US flag on the moon survive? Now imagine entire bases on bodies where almost no erosion occurs. Not to mention artifacts in orbital space, where preservation is effectively for ever. If a satellite was in geostationary orbit around Venus or Mars, how long would it remain in place? Forever? Or are there mechanisms that will inevitably disturb it?Nothing lasts forever. Even our satellites in geostationary orbit will I believe after a million years return to Earth and he's talking about far longer time scales than that.
Quote from: Star One on 04/29/2017 04:47 pmQuote from: M.E.T. on 04/29/2017 03:36 pmAs much as the idea appeals to me I find it difficult to see how evidence of prior spacefaring civilizations would not be visible in orbit or on moons etc. How long will the US flag on the moon survive? Now imagine entire bases on bodies where almost no erosion occurs. Not to mention artifacts in orbital space, where preservation is effectively for ever. If a satellite was in geostationary orbit around Venus or Mars, how long would it remain in place? Forever? Or are there mechanisms that will inevitably disturb it?Nothing lasts forever. Even our satellites in geostationary orbit will I believe after a million years return to Earth and he's talking about far longer time scales than that.But M.E.T. has a point about landing sites on our Moon and similar bodies. They would be expected to preserve visible evidence for billions of years, unless they happen to be hit by impactors. If there were multiple landing sites on the Moon, it's unlikely all were destroyed by impacts.
Quote from: ChrisWilson68 on 04/29/2017 05:02 pmQuote from: Star One on 04/29/2017 04:47 pmQuote from: M.E.T. on 04/29/2017 03:36 pmAs much as the idea appeals to me I find it difficult to see how evidence of prior spacefaring civilizations would not be visible in orbit or on moons etc. How long will the US flag on the moon survive? Now imagine entire bases on bodies where almost no erosion occurs. Not to mention artifacts in orbital space, where preservation is effectively for ever. If a satellite was in geostationary orbit around Venus or Mars, how long would it remain in place? Forever? Or are there mechanisms that will inevitably disturb it?Nothing lasts forever. Even our satellites in geostationary orbit will I believe after a million years return to Earth and he's talking about far longer time scales than that.But M.E.T. has a point about landing sites on our Moon and similar bodies. They would be expected to preserve visible evidence for billions of years, unless they happen to be hit by impactors. If there were multiple landing sites on the Moon, it's unlikely all were destroyed by impacts.Just because some natural features on certain bodies can last a long time does not automatically equate to the same being true of complex artificial structures.
If the Apollo landings had happened 3 billion years ago, I believe that we would have noticed them with our mapping of the lunar surface. I see no credible mechanism for their deterioration in a way that would make them not be apparent 3 billion years later, unless they all happened to be hit by large impacts.
Quote from: M.E.T. on 04/29/2017 03:36 pmAs much as the idea appeals to me I find it difficult to see how evidence of prior spacefaring civilizations would not be visible in orbit or on moons etc. How long will the US flag on the moon survive? Now imagine entire bases on bodies where almost no erosion occurs. Not to mention artifacts in orbital space, where preservation is effectively for ever. If a satellite was in geostationary orbit around Venus or Mars, how long would it remain in place? Forever? Or are there mechanisms that will inevitably disturb it?I agree. It seems like there's a lot of evidence against the idea.A civilization that had expanded throughout the solar system would have been likely to leave noticeable sites on bodies throughout the system, including our moon and other airless bodies without any erosion processes to destroy the evidence, and we should have found it by now.The only fix I can think of for that is to assume the earlier civilization decided to leave and return our system to a natural state, removing all clear evidence of its existence. Think of places where we've removed our structures to restore wetlands or other natural habitats.But then there's still the problem of where the civilization arose. We arose from a long line of complex organisms that left a rich fossil legacy over hundreds of millions of years. It's not really plausible that a civilization arose a billion years ago without coming from hundreds of millions of years of complex organisms and there is no record at all that we've found of that. Are we to believe that they dug up every fossil everywhere on the Earth no matter how deep for a 500 million year period?They could have arisen from some species in the fossil record after the Cambrian explosion, but then they're relatively recent and it would be hard for them to erase every artifact they ever left. Imagine trying to find every pot shard and every arrowhead our ancestors left throughout the planet to erase the record of our existence. And why? When we restore a natural environment, it's so that natural systems can go back to work, not to try to erase evidence for future archaeologists.If they didn't arise on Earth but they were indigenous to our Solar System, where did they arise? If they arose on Mars, we would expect that they arose from hundreds of millions of years of ancestors that left a fossil record, and we've poked around on Mars enough that we would expect to have noticed some of that fossil record by now. Most other bodies aren't really conducive to evolution of a large, complex life form, except the Earth, Mars, and Venus.So, Venus seems like the only possibility left. Maybe Venus was once more friendly to life and it arose, built a civilization, expanded to the solar system, then restored the system to a mostly natural state and left. It seems unlikely, but not entirely impossible.
Quote from: ChrisWilson68 on 04/29/2017 05:53 pmIf the Apollo landings had happened 3 billion years ago, I believe that we would have noticed them with our mapping of the lunar surface. I see no credible mechanism for their deterioration in a way that would make them not be apparent 3 billion years later, unless they all happened to be hit by large impacts.I'd think that in 3 billion years a large impact nearby would be rather likely to have happened. 3 billion years also a very long time for erosion due to micrometeorite impacts to take place.
Most craters you see today came from the Late Heavy Bombardment that came in the closing stages of the formation of the solar system around 3.8 billion years ago.
Folks, this stuff about artifacts in the solar system is far OT from "Boyajians Star Updates And Discussion" I'd suggest a split starting at http://forum.nasaspaceflight.com/index.php?topic=41704.msg1670474#msg1670474QuoteMost craters you see today came from the Late Heavy Bombardment that came in the closing stages of the formation of the solar system around 3.8 billion years ago.No, most large impact craters date from billions of years ago. Even the youngest areas of the moon are heavily impact gardened once you get down to 10s of meter scales relevant to preserving something like Apollo sites.
Based on what evidence are you claiming this?
We also observe a secondary cratering process that we estimate churns the top two centimetres of regolith on a timescale of 81,000 years—more than a hundred times faster than previous models estimated from meteoritic impacts (ten million years)
And even with all the craters from the LHB, the majority of the surface of the moon is not craters, it's just marked with craters, with non-crater areas between the craters.
AbstractLandscape evolution on the Moon is dominated by impact cratering in the post-maria period.In this study, we mapped 800 m to 5 km diameter craters on 30% of the lunar maria and extracted theirtopographic profiles from digital terrain models created using the Kaguya Terrain Camera. We thencharacterized the degradation of these craters using a topographic diffusion model. Because craters have awell-understood initial morphometry, these data provide insight into erosion on the Moon and the topographicdiffusivity of the lunar surface as a function of time. The average diffusivity we calculate over the past 3 Ga is~5.5 m2/Myr. With this diffusivity, after 3 Ga, a 1 km diameter crater is reduced to approximately ~52% of itsinitial depth and a 300 m diameter crater is reduced to only ~7% of its initial depth, and craters smaller than~200–300 m are degraded beyond recognition. Our results also allow estimation of the age of individualcraters on the basis of their degradation state, provide a constraint on the age of mare units, and enablemodeling of how lunar terrain evolves as a function of its topography.
Not to mention artifacts in orbital space, where preservation is effectively for ever. If a satellite was in geostationary orbit around Venus or Mars, how long would it remain in place? Forever? Or are there mechanisms that will inevitably disturb it?
How about the stuff in heliocentric orbits? We find 10 meter sized asteroids all the time, presumably billions of years old.