Say we find extraterrestrial life, how to prove it?

http://phys.org/news/2015-07-extraterrestrial-life.html

If we find what we think are signs of life where we cannot actually send probes and return specimens how do we prove it is actually life we are seeing in our telescopes?

Mars is another story, close enough we can send probes that can return samples to Earth and we can analyse the stuff to death, but a telescope view?

Originally posted by sonhouse
http://phys.org/news/2015-07-extraterrestrial-life.html

If we find what we think are signs of life where we cannot actually send probes and return specimens how do we prove it is actually life we are seeing in our telescopes?

Mars is another story, close enough we can send probes that can return samples to Earth and we can analyse the stuff to death, but a telescope view?

The same as we do for most astronomy: we just keep looking until all the clues indicate certainty. It will go like this as the clues add up:
1. Life suspected.
2. Life likely.
3. Life most likely.
4. Life almost certain.
5. Life pretty much definite.

Of course it may turn out in some cases that the evidence just doesn't add up and life is no longer the best explanation.

Originally posted by twhitehead
The same as we do for most astronomy: we just keep looking until all the clues indicate certainty. It will go like this as the clues add up:
1. Life suspected.
2. Life likely.
3. Life most likely.
4. Life almost certain.
5. Life pretty much definite.

Of course it may turn out in some cases that the evidence just doesn't add up and life is no longer the best explanation.

Unless we get one mm resolution at say 100 light years and actually see bugs or plants or animals moving around, which would be a telescope lens approximately the size of the solar system🙂 then we have to wait for actual probes to get to wherever the planet is in the galaxy. THAT won't be happening in this century for sure!

Originally posted by sonhouse
http://phys.org/news/2015-07-extraterrestrial-life.html

If we find what we think are signs of life where we cannot actually send probes and return specimens how do we prove it is actually life we are seeing in our telescopes?

Mars is another story, close enough we can send probes that can return samples to Earth and we can analyse the stuff to death, but a telescope view?

We can't

Originally posted by Metal Brain
We can't

Can't what? Retrieve a soil sample from Mars? Analyze light well enough to say there is definite life on planet X? We can't at this time, but 100 years from now, given the possibility of scientific development we have seen over the last few centuries, who knows what the future will bring. For instance, I said a telescope with a mirror the size of the solar system would be needed to get 1 mm resolution at 100 light years but it really 'only' takes a mirror 60 million miles across🙂 But it doesn't have to be a single mirror that size, there can be several mirrors spread out by 60 million miles and signals combined.

Originally posted by sonhouse
Unless we get one mm resolution at say 100 light years and actually see bugs or plants or animals moving around, which would be a telescope lens approximately the size of the solar system🙂 then we have to wait for actual probes to get to wherever the planet is in the galaxy. THAT won't be happening in this century for sure!

Astronomy has taught us that we can learn a remarkable amount from a minuscule amount of data if we just interpret it correctly. Almost no planets outside the solar system have been imaged directly. The vast majority are detected by either measuring the gravitational effect they have on their star, (wobble), or the starlight they block out as they pass in front of the star (transit). Yet we are getting a pretty good idea about the size, mass, and orbits of thousands of planets this way.
It won't be long before we can get good resolution spectra of some planets. At that time we can start analysing chemical composition of atmospheres. As I said earlier, initial results would be far from conclusive, but I see no reason to think it would be impossible to identify the existence of life from spectra alone.

What you really need to ask, is whether or not an alien in a nearby star system with earth-like technology could detect us.

Originally posted by twhitehead
Astronomy has taught us that we can learn a remarkable amount from a minuscule amount of data if we just interpret it correctly. Almost no planets outside the solar system have been imaged directly. The vast majority are detected by either measuring the gravitational effect they have on their star, (wobble), or the starlight they block out as they pass in ...[text shortened]... , is whether or not an alien in a nearby star system with earth-like technology could detect us.

We already know if an alien technology exists on the other side of the GALAXY they could detect us, because we already can detect us at that distance, say 50,000 light years, at least detect the presence of RF or light that is clearly artificial in origin.

That is one reason for I think it was Fermi who said 'Where are they"?

A lot of issues there as to why we have not so far detected extraterrestrial technology, like the trend we see today where we may not be transmitting in RF at all in another 100 years, but going to fiber optics or local lasers and such. So that would lead to a situation where we would only be broadcasting a 200 year wide wavefront of energy that could be detected by aliens. So if some civilization 2000 light years away sets up antennae our signal would not even arrive for 2000 odd years so they may have also given up using RF so they wouldn't detect us either. Lots of scenarios where detection would not take place in spite of signals being present at one time or another in the galaxy.

Originally posted by sonhouse
We already know if an alien technology exists on the other side of the GALAXY they could detect us, because we already can detect us at that distance, say 50,000 light years, at least detect the presence of RF or light that is clearly artificial in origin.

Actually, no, I don't think so. I don't think we have yet even done surveys of the very closest stars that would pick up human like signals. Light? That is out of the question with current technology. There could be human like light sources on Pluto and we wouldn't know (until next week at least).

Originally posted by twhitehead
Actually, no, I don't think so. I don't think we have yet even done surveys of the very closest stars that would pick up human like signals. Light? That is out of the question with current technology. There could be human like light sources on Pluto and we wouldn't know (until next week at least).

Actually Hubble could pick up 'human light sources' on Pluto no trouble.

By looking at the spectra. [and it would be glowing brightly in IR that would stand out like a sore thumb.]

Radio signals we could easily pick out from a long way off... if we look in the right place at the right time.

Originally posted by googlefudge
Actually Hubble could pick up 'human light sources' on Pluto no trouble.

By looking at the spectra. [and it would be glowing brightly in IR that would stand out like a sore thumb.]

Has anyone done so?
Keep in mind also that the dark side of Pluto is always facing away from us.

Radio signals we could easily pick out from a long way off... if we look in the right place at the right time.
And have we?
Take the nearest stars. If they were transmitting the same sort of radio waves that earth is currently transmitting, would we have detected it yet? I don't think so.

Keep in mind that half of Pluto's moons were only discovered in the last few years.

Originally posted by sonhouse
Can't what? Retrieve a soil sample from Mars? Analyze light well enough to say there is definite life on planet X? We can't at this time, but 100 years from now, given the possibility of scientific development we have seen over the last few centuries, who knows what the future will bring. For instance, I said a telescope with a mirror the size of the solar ...[text shortened]... ror that size, there can be several mirrors spread out by 60 million miles and signals combined.

I answered your first question. As you said, Mars is a different matter.

Originally posted by twhitehead
Keep in mind that half of Pluto's moons were only discovered in the last few years.

Yeah, but that's the point, isn't it? Those moons aren't actively broadcasting anything. They're dark lumps of rock that merely reflect what's around them, which is more rock. If they were broadcasting radio waves, as opposed to reflecting a broad, generic spectrum, we'd a) have detected them a long time ago and b) know that there was something interesting there. But they don't, which is why we've only just found them, because there isn't anyone there.

Originally posted by twhitehead
Has anyone done so?
Keep in mind also that the dark side of Pluto is always facing away from us.

[b]Radio signals we could easily pick out from a long way off... if we look in the right place at the right time.
And have we?
Take the nearest stars. If they were transmitting the same sort of radio waves that earth is currently transmitting, would we have detected it yet? I don't think so.[/b]

Has anyone done so?
Keep in mind also that the dark side of Pluto is always facing away from us.

Um, no it isn't. Pluto is tidally locked to Charon, not the Sun.

I would recommend having a look on this page about 'stealth in space' which deals with how easy it
is to detect manned spacecraft due to thermal emissions even with current technology.

http://www.projectrho.com/public_html/rocket/spacewardetect.php#nostealth

".....The Space Shuttle's much weaker main engines could be detected past the orbit of Pluto. The Space Shuttle's manoeuvering thrusters could be seen as far as the asteroid belt. And even a puny ship using ion drive to thrust at a measly 1/1000 of a g could be spotted at one astronomical unit.

As of 2013, the Voyager 1 space probe is about 18 billion kilometers away from Terra and its radio signal is a pathetic 20 watts (or about as dim as the light bulb in your refrigerator). But as faint as it is, the Green Bank telescope can pick it out from the background noise in one second flat.

This is with current off-the-shelf technology. Presumably future technology would be better."

Radio signals we could easily pick out from a long way off... if we look in the right place at the right time.[/b]
And have we?
Take the nearest stars. If they were transmitting the same sort of radio waves that earth is currently transmitting, would we have detected it yet? I don't think so.

Have you ever heard of SETI ???????

They have spent decades using giant telescopes to search for artificial signals from nearby stars.

They haven't found anything, but that's not because they couldn't detect Earth like radio transmissions from
planets around these stars. It's because nobody was emitting Earth like emissions from around these
stars.

Originally posted by twhitehead
Keep in mind that half of Pluto's moons were only discovered in the last few years.

Pluto's moons, like Pluto itself, are freezing nitrogen solid in a vacuum cold.

If you put human living quarters on them then they will at a minimum be blasting
out thermal radiation from the people living in 20 degree C accommodations.
More realistically you have the heat plume from the nuclear freaking reactors they
are using for power.

They are going to be glowing very brightly in IR against a background of 3k.

Dead easy to spot, without any surface lights.