Plutonium - the last ironic trace of civilization?

[cph]

At least 3 million years are required to form a geological strata (of say 7 ft?). What

remanents of a culture might survive? Plastic pieces; or nothing at all? Our world has

hundreds of tons of plutonium; plus all reactors forming plutonium. The halve life of

plutonium is very long; so it would survive on our planet, and in our broader stellar system

if for example we diverted an asteroid by nuclear warhead means. Likewise for exploration of

terrestrial planets of habitat zone of another stellar system, might the only trace of

civilization be that of plutonium? Stars form in multiple; so therefore our Sun has sister

stellar systems, very close, and ascertainable via dedicated infrared telescope detection of

'cold' gas giants. In addition to spectroscopic detection of oxygen (sign of photosynthesis)

in the atmosphere, might search for plutonium be of interest?

 

[Jack21222]

I strongly doubt that enough plutonium can be generated to be detected from many light years away, but I don't have the math to back it up.

 

[Max™]

Layers of crushed automobiles will be our fossils is what I've heard tossed around, sounds pretty accurate to me.

 

[Vagn]

Wouldn't unusual deposits of metals in plsces where they would not naturally occur would be evidence of a civilisation having previously been on a planet. I think that this would probably be the final clue to our existence.

 

[DrDu]

There was an article in scientific american some maybe 3 years ago about what would be left from our civilization if it would stop today. Most iron based constructions (including sky scrapers, automobiles) wouldn't last very long. Brass statues would last for more than 10000 years if I remember correctly.
Pu 239 has a half life time of 29000years, so, at least on astronomical orders (millions of years) it would disappear pretty soon.

 

[Borek]

Plenty of places that could be easily recognized as being created by civilization. Think about centers of large cities - even after millions years, when they will be leveled by the erosion, it would be obvious that combination of materials/minerals present in the place is not natural. Then, just like we see fossils, many of objects we use would get fossilized this way or another. There are many large scale engineering objects, so it is likely that some will be recognizable after many years - not because they will be still standing, but because we shaped the ground using rulers, and straight lines are not something that happens frequently in nature.

 

[cph]

Also satellites in orbit would essentially stay in orbit forever. Hence another indicator of past civilization. Just as we easily see satellites from ground, so optical detection, from near space, of reflected light would indicate vanished civilizations, indefinitely into the future.

 

[Borek]

Also satellites in orbit would essentially stay in orbit forever.

It depends on how high the orbit is. No idea about geostationary, but those at few hundred kilometers are falling down because of the atmospheric drag. Yes, atmospheric. Very thin, dense enough to slow them down.

 

[Kritmiss]

The result of the decay of the plutonium would be an unusual isotopic mix of uranium with a little neptunium in there also, that would be good evidence lasting for long enough! A resource of U-235 for the distant future...?

 

[ideasrule]

It depends on how high the orbit is. No idea about geostationary, but those at few hundred kilometers are falling down because of the atmospheric drag. Yes, atmospheric. Very thin, dense enough to slow them down.

Just to give some perspective, the expected lifetime of KEO, which will be in a 1800 km orbit, is 50 000 years: http://en.wikipedia.org/wiki/KEO. For geostationary orbits, the atmosphere will probably be negligible, but gravitational perturbations from the Moon and Sun, solar pressure, and interactions with the magnetic field will change the orbit, possibly causing re-entry or sending the sat into space.

P.S. I remember reading about KEO as a kid, and even at the time the launch date had been pushed back a few times. It's very surprising and saddening to know that the sat may never launch.

 

[eachus]

The two LAGEOS satellites are expected to remain in orbit for about 8.4 million years. Today they are (intentionally) very easy to find--they are studded all over with corner reflectors. These mirrors and the weight of the satellites allow for extremely precise distance measurements from the Earth's surface. (Today GPS satellites allow for even more precise measurements, but the techniques used were not developed at the time the LAGEOS satellites were launched.)

I suppose in a few million years interplanetary dust and the solar wind will have deteriorated the corner reflectors, and there is always the chance of running into a small (or large) comet or asteroid. So I vote for the lunar landing sites as the most enduring (findable) relic of our civilization. (The Pioneer and Voyager spacecraft are going to be pretty hard to find in ten million years or so, even given precise trajectory data. ;-)

 

[alanali]

What about the radio waves we've been broadcasting for more than a century?

 

[Chronos]

Radio signals fade to undetectable levels after traveling a few light years. My money is on the lunar laser ranging mirrors left on the surface of the moon.