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Ancient Xeno-"archaeology"/paleontology
http://sfrpg-discussion.net/viewtopic.php?f=41&t=3229
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Author:  Sir Chaos [ Tue Nov 07, 2017 4:38 pm ]
Post subject:  Re: Ancient Xeno-"archaeology"/paleontology

Cyborg IM1 wrote:
In space, it is much more likely that the basic object would still be around. Nothing would work. Millions of years of ionizing radiation and micro-meteor impacts would make most of them fused solid. The closer they were to the habitable zone, the more damage. I would suspect that something in Earth/Lunar orbit for 65-70 million years would look like a weird asteroid with unusual compositions rather than something recognizable as an alien vessel. In the outer planetary system, they would be better preserved, provided they were not too close to a magnetic field or other fun planetary phenomena.


Then perhaps the best bet would be a disabled or wrecked ship left drifting in *very* eccentric orbit that just happens to take it near the habitable zone at the time of the campaign.

If the orbit is eccentric enough, the object wouldn´t spend that much time near the sun - remember, an object in an eccentric orbit moves faster the closer it is to the star. With an orbital period of, say, a million years, it´d probably only spend a decade or two at a time in the "populated" regions of a star system, call it 1,000 years total since the Gardeners disappeared.

Author:  Golan2072 [ Tue Nov 07, 2017 5:58 pm ]
Post subject:  Re: Ancient Xeno-"archaeology"/paleontology

Hmmm... Could lead to some Oort cloud xeno-archaeology.

I wonder what will happen to remains and structures underground on Luna-like worlds. In a deep cave, away from micrometeorites and most radiation...

Author:  thrash [ Tue Nov 07, 2017 8:15 pm ]
Post subject:  Re: Ancient Xeno-"archaeology"/paleontology

Cyborg IM1 wrote:
I would suspect that something in Earth/Lunar orbit for 65-70 million years would look like a weird asteroid with unusual compositions rather than something recognizable as an alien vessel.

Note that orbits of small bodies in the Solar System are unpredictable (chaotic) on timescales shorter than this. As their orbits evolve, objects almost always encounter something that kicks them out into a different region. Near Earth Objects have stable orbital lifetimes of ~5 million years; temporary satellites and space debris last on the order of a few tens of thousands of years, at best. Also, we would have seen something the size of a spacecraft (unless the aliens are Lilliputian) in Earth-Moon orbit pretty quickly.

If you want something to hang around, put it in the Main Belt well away from the Kirkwood gaps, the Jupiter Trojan clusters, or one of the asteroid dynamic families (Hungarias, etc.) away from the Main Belt. We would have a hard time spotting a 10 m object at those ranges, and the volumes of space they fill are so vast that going there to look won't help much.

Author:  Sir Chaos [ Tue Nov 07, 2017 9:26 pm ]
Post subject:  Re: Ancient Xeno-"archaeology"/paleontology

Golan2072 wrote:
Hmmm... Could lead to some Oort cloud xeno-archaeology.


I poked around on Wikipedia for the last post, looking up something I dimly remembered - and found a comet with a 7.1 million year orbital period and an aphelion of 73,000 AU - 1.15 light-years!

I doubt it´s really feasible to search a cubic light-year or more around a star for a relatively small object that has a rather small chance of being there to begin with. I figure if such objects are found at all, it´s because their orbits takes them within a couple of AU of the star.

Quote:
I wonder what will happen to remains and structures underground on Luna-like worlds. In a deep cave, away from micrometeorites and most radiation...


Could be relatively intact... or at least as intact as it was when abandoned. Especially if it was breached - deliberately or by an attack or accident - and is thus under vacuum inside.

Although... after 65 million years, I assume all atmosphere would have leaked out of an otherwise intact structure, too.

Either way, nothing would work any more, but structural elements and inert chunks of machinery would be a fairly impressive find from that long ago...

Author:  Agemegos [ Tue Nov 07, 2017 10:16 pm ]
Post subject:  Re: Ancient Xeno-"archaeology"/paleontology

Cyborg IM1 wrote:
Remember, that what we dig up isn't the actual eggshell or dino bone, but mineralized deposits that have replaced the bone through the eons.


That's true-ish of bone, in which the original calcium phosphate is usually replaced by something else, though a former classmate of mine spent a few years excavating bones from the Riversleigh Limestones, twenty-odd to eleven thousand years old, and he told me that what he was recovering was still bone (he was removing the calcium carbonate matrix from the bony remains by soaking blocks in acetic acid). But eggshells are calcium carbonate to begin with, and that's stable so long as the environment is not acidic.

Besides, the footprints are preserved in the original sand and clay.

Author:  Agemegos [ Tue Nov 07, 2017 10:47 pm ]
Post subject:  Re: Ancient Xeno-"archaeology"/paleontology

The survival of techological artifacts on planetary surfaces depends to a great extent on whether their environment is accumulating sediment or being eroded, and therefore on whether it is exposed to weathering. Almost nothing will survive sixty-five million years of weathering, but a lot of surprisingly delicate things will survive if they are buried, including eggshells, footprints, and the impressions e.g. of bones that may remain recogniseable while being filled with precipitates such as lime, silica, haematite…. Small featues and delicate structures have been preserved 200 million years in favourable locations.

As for preserving the original material, that depends to a considerable extent on the chemistry of the sediments. Acidic soils destroy base metals and even concrete in fairly short order; I wouldn't count even on stainless steel to last. But in limy sediments concrete is just a funny-shaped lime-cemented conglomerate rock, and will last indefinitely, and I think that any metal that tends to form a passiviating layer of oxide can last a very long time. Ceramics and some glasses, too, are chemically pretty much the same as rocks that have survived longer than that.

In areas of tectonic uplift nothing much will survive. In areas that are sinking and accumulating sediment, expect concrete, bricks, and tiles to survive, including some structures. Massive ceramics and glass artifacts will survive, too; people always think of lavatory pans, but the insulators from ling-distance high-voltage electric transmission lines are an even better bet. I don't know whether any likely environment is alkaline and anoxic enough for stainless steel to survive, but jewelry in gold and platinum can probably survive of not subject to mechanical erosion. cut facets on diamonds, sapphires, rubies, and garnets will probably remain recognisable through a hell of a beating.

Author:  Cyborg IM1 [ Wed Nov 08, 2017 4:53 pm ]
Post subject:  Re: Ancient Xeno-"archaeology"/paleontology

I would think that after 65 million years, you might get both sedimentation and erosion in the same area - first it gets buried, then it get eroded back to the surface.

Author:  strontygirl [ Wed Nov 08, 2017 6:09 pm ]
Post subject:  Re: Ancient Xeno-"archaeology"/paleontology

Ceramics are not found in nature. Clays are. Metamorphosed (subjected to intense heat and pressure) clay rocks are. But ceramics are not. If your geologists start doing geochemistry and mineralogy tests on those odd looking little pebbles in the 65 million year old sediment, and those pebbles happen to be eroded fragments of house bricks, breeze blocks, roof tiles, your coffee mug or your toilet (i.e. ceramics), they'll get a signature for a material which was fired at an extremely high temperature in a high oxygen atmosphere and at 1 atmosphere pressure. So it's been heated like it is deep in the crust... but wait, it was at 1 atm pressure, so that theory is wrong. So a lava flow sat on top of it at the surface! But wait... there was lots of oxygen present, so that theory is wrong. Good lord, it must have been fired in a kiln!

Author:  Sir Chaos [ Wed Nov 08, 2017 6:30 pm ]
Post subject:  Re: Ancient Xeno-"archaeology"/paleontology

strontygirl wrote:
Ceramics are not found in nature. Clays are. Metamorphosed (subjected to intense heat and pressure) clay rocks are. But ceramics are not. If your geologists start doing geochemistry and mineralogy tests on those odd looking little pebbles in the 65 million year old sediment, and those pebbles happen to be eroded fragments of house bricks, breeze blocks, roof tiles, your coffee mug or your toilet (i.e. ceramics), they'll get a signature for a material which was fired at an extremely high temperature in a high oxygen atmosphere and at 1 atmosphere pressure. So it's been heated like it is deep in the crust... but wait, it was at 1 atm pressure, so that theory is wrong. So a lava flow sat on top of it at the surface! But wait... there was lots of oxygen present, so that theory is wrong. Good lord, it must have been fired in a kiln!


Image

(SCNR)

Author:  Agemegos [ Thu Nov 09, 2017 12:28 am ]
Post subject:  Re: Ancient Xeno-"archaeology"/paleontology

Cyborg IM1 wrote:
I would think that after 65 million years, you might get both sedimentation and erosion in the same area - first it gets buried, then it get eroded back to the surface.

Yes, of course. Nevertheless, we have some sediments that were laid down 65 million years ago and were never eroded away in subsequent episodes of uplift and erosion.

Inside of volumes like that, very delicate stuff can survive. Outside them few things can.

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